[v7] Add AutoFDO and Propeller support for Clang build

[PATCH v7 1/7] Add AutoFDO support for Clang build

Posted by Rong Xu 3 weeks, 1 day ago

Add the build support for using Clang's AutoFDO. Building the kernel
with AutoFDO does not reduce the optimization level from the
compiler. AutoFDO uses hardware sampling to gather information about
the frequency of execution of different code paths within a binary.
This information is then used to guide the compiler's optimization
decisions, resulting in a more efficient binary. Experiments
showed that the kernel can improve up to 10% in latency.

The support requires a Clang compiler after LLVM 17. This submission
is limited to x86 platforms that support PMU features like LBR on
Intel machines and AMD Zen3 BRS. Support for SPE on ARM 1,
 and BRBE on ARM 1 is part of planned future work.

Here is an example workflow for AutoFDO kernel:

1) Build the kernel on the host machine with LLVM enabled, for example,
       $ make menuconfig LLVM=1
    Turn on AutoFDO build config:
      CONFIG_AUTOFDO_CLANG=y
    With a configuration that has LLVM enabled, use the following
    command:
       scripts/config -e AUTOFDO_CLANG
    After getting the config, build with
      $ make LLVM=1

2) Install the kernel on the test machine.

3) Run the load tests. The '-c' option in perf specifies the sample
   event period. We suggest     using a suitable prime number,
   like 500009, for this purpose.
   For Intel platforms:
      $ perf record -e BR_INST_RETIRED.NEAR_TAKEN:k -a -N -b -c <count> \
        -o <perf_file> -- <loadtest>
   For AMD platforms:
      The supported system are: Zen3 with BRS, or Zen4 with amd_lbr_v2
     For Zen3:
      $ cat proc/cpuinfo | grep " brs"
      For Zen4:
      $ cat proc/cpuinfo | grep amd_lbr_v2
      $ perf record --pfm-events RETIRED_TAKEN_BRANCH_INSTRUCTIONS:k -a \
        -N -b -c <count> -o <perf_file> -- <loadtest>

4) (Optional) Download the raw perf file to the host machine.

5) To generate an AutoFDO profile, two offline tools are available:
   create_llvm_prof and llvm_profgen. The create_llvm_prof tool is part
   of the AutoFDO project and can be found on GitHub
   (https://github.com/google/autofdo), version v0.30.1 or later. The
   llvm_profgen tool is included in the LLVM compiler itself. It's
   important to note that the version of llvm_profgen doesn't need to
   match the version of Clang. It needs to be the LLVM 19 release or
   later, or from the LLVM trunk.
      $ llvm-profgen --kernel --binary=<vmlinux> --perfdata=<perf_file> \
        -o <profile_file>
   or
      $ create_llvm_prof --binary=<vmlinux> --profile=<perf_file> \
        --format=extbinary --out=<profile_file>

   Note that multiple AutoFDO profile files can be merged into one via:
      $ llvm-profdata merge -o <profile_file>  <profile_1> ... <profile_n>

6) Rebuild the kernel using the AutoFDO profile file with the same config
   as step 1, (Note CONFIG_AUTOFDO_CLANG needs to be enabled):
      $ make LLVM=1 CLANG_AUTOFDO_PROFILE=<profile_file>

Co-developed-by: Han Shen <shenhan@google.com>
Signed-off-by: Han Shen <shenhan@google.com>
Signed-off-by: Rong Xu <xur@google.com>
Suggested-by: Sriraman Tallam <tmsriram@google.com>
Suggested-by: Krzysztof Pszeniczny <kpszeniczny@google.com>
Suggested-by: Nick Desaulniers <ndesaulniers@google.com>
Suggested-by: Stephane Eranian <eranian@google.com>
Tested-by: Yonghong Song <yonghong.song@linux.dev>
Tested-by: Yabin Cui <yabinc@google.com>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Kees Cook <kees@kernel.org>
---
 Documentation/dev-tools/autofdo.rst | 168 ++++++++++++++++++++++++++++
 Documentation/dev-tools/index.rst   |   1 +
 MAINTAINERS                         |   7 ++
 Makefile                            |   1 +
 arch/Kconfig                        |  20 ++++
 arch/x86/Kconfig                    |   1 +
 scripts/Makefile.autofdo            |  22 ++++
 scripts/Makefile.lib                |  10 ++
 tools/objtool/check.c               |   1 +
 9 files changed, 231 insertions(+)
 create mode 100644 Documentation/dev-tools/autofdo.rst
 create mode 100644 scripts/Makefile.autofdo

diff --git a/Documentation/dev-tools/autofdo.rst b/Documentation/dev-tools/autofdo.rst
new file mode 100644
index 0000000000000..1f0a451e9ccd3
--- /dev/null
+++ b/Documentation/dev-tools/autofdo.rst
@@ -0,0 +1,168 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+===================================
+Using AutoFDO with the Linux kernel
+===================================
+
+This enables AutoFDO build support for the kernel when using
+the Clang compiler. AutoFDO (Auto-Feedback-Directed Optimization)
+is a type of profile-guided optimization (PGO) used to enhance the
+performance of binary executables. It gathers information about the
+frequency of execution of various code paths within a binary using
+hardware sampling. This data is then used to guide the compiler's
+optimization decisions, resulting in a more efficient binary. AutoFDO
+is a powerful optimization technique, and data indicates that it can
+significantly improve kernel performance. It's especially beneficial
+for workloads affected by front-end stalls.
+
+For AutoFDO builds, unlike non-FDO builds, the user must supply a
+profile. Acquiring an AutoFDO profile can be done in several ways.
+AutoFDO profiles are created by converting hardware sampling using
+the "perf" tool. It is crucial that the workload used to create these
+perf files is representative; they must exhibit runtime
+characteristics similar to the workloads that are intended to be
+optimized. Failure to do so will result in the compiler optimizing
+for the wrong objective.
+
+The AutoFDO profile often encapsulates the program's behavior. If the
+performance-critical codes are architecture-independent, the profile
+can be applied across platforms to achieve performance gains. For
+instance, using the profile generated on Intel architecture to build
+a kernel for AMD architecture can also yield performance improvements.
+
+There are two methods for acquiring a representative profile:
+(1) Sample real workloads using a production environment.
+(2) Generate the profile using a representative load test.
+When enabling the AutoFDO build configuration without providing an
+AutoFDO profile, the compiler only modifies the dwarf information in
+the kernel without impacting runtime performance. It's advisable to
+use a kernel binary built with the same AutoFDO configuration to
+collect the perf profile. While it's possible to use a kernel built
+with different options, it may result in inferior performance.
+
+One can collect profiles using AutoFDO build for the previous kernel.
+AutoFDO employs relative line numbers to match the profiles, offering
+some tolerance for source changes. This mode is commonly used in a
+production environment for profile collection.
+
+In a profile collection based on a load test, the AutoFDO collection
+process consists of the following steps:
+
+#. Initial build: The kernel is built with AutoFDO options
+   without a profile.
+
+#. Profiling: The above kernel is then run with a representative
+   workload to gather execution frequency data. This data is
+   collected using hardware sampling, via perf. AutoFDO is most
+   effective on platforms supporting advanced PMU features like
+   LBR on Intel machines.
+
+#. AutoFDO profile generation: Perf output file is converted to
+   the AutoFDO profile via offline tools.
+
+The support requires a Clang compiler LLVM 17 or later.
+
+Preparation
+===========
+
+Configure the kernel with::
+
+   CONFIG_AUTOFDO_CLANG=y
+
+Customization
+=============
+
+The default CONFIG_AUTOFDO_CLANG setting covers kernel space objects for
+AutoFDO builds. One can, however, enable or disable AutoFDO build for
+individual files and directories by adding a line similar to the following
+to the respective kernel Makefile:
+
+- For enabling a single file (e.g. foo.o) ::
+
+   AUTOFDO_PROFILE_foo.o := y
+
+- For enabling all files in one directory ::
+
+   AUTOFDO_PROFILE := y
+
+- For disabling one file ::
+
+   AUTOFDO_PROFILE_foo.o := n
+
+- For disabling all files in one directory ::
+
+   AUTOFDO_PROFILE := n
+
+Workflow
+========
+
+Here is an example workflow for AutoFDO kernel:
+
+1)  Build the kernel on the host machine with LLVM enabled,
+    for example, ::
+
+      $ make menuconfig LLVM=1
+
+    Turn on AutoFDO build config::
+
+      CONFIG_AUTOFDO_CLANG=y
+
+    With a configuration that with LLVM enabled, use the following command::
+
+      $ scripts/config -e AUTOFDO_CLANG
+
+    After getting the config, build with ::
+
+      $ make LLVM=1
+
+2) Install the kernel on the test machine.
+
+3) Run the load tests. The '-c' option in perf specifies the sample
+   event period. We suggest using a suitable prime number, like 500009,
+   for this purpose.
+
+   - For Intel platforms::
+
+      $ perf record -e BR_INST_RETIRED.NEAR_TAKEN:k -a -N -b -c <count> -o <perf_file> -- <loadtest>
+
+   - For AMD platforms:
+
+     The supported systems are: Zen3 with BRS, or Zen4 with amd_lbr_v2. To check,
+
+     For Zen3::
+
+      $ cat proc/cpuinfo | grep " brs"
+
+     For Zen4::
+
+      $ cat proc/cpuinfo | grep amd_lbr_v2
+
+     The following command generated the perf data file::
+
+      $ perf record --pfm-events RETIRED_TAKEN_BRANCH_INSTRUCTIONS:k -a -N -b -c <count> -o <perf_file> -- <loadtest>
+
+4) (Optional) Download the raw perf file to the host machine.
+
+5) To generate an AutoFDO profile, two offline tools are available:
+   create_llvm_prof and llvm_profgen. The create_llvm_prof tool is part
+   of the AutoFDO project and can be found on GitHub
+   (https://github.com/google/autofdo), version v0.30.1 or later.
+   The llvm_profgen tool is included in the LLVM compiler itself. It's
+   important to note that the version of llvm_profgen doesn't need to match
+   the version of Clang. It needs to be the LLVM 19 release of Clang
+   or later, or just from the LLVM trunk. ::
+
+      $ llvm-profgen --kernel --binary=<vmlinux> --perfdata=<perf_file> -o <profile_file>
+
+   or ::
+
+      $ create_llvm_prof --binary=<vmlinux> --profile=<perf_file> --format=extbinary --out=<profile_file>
+
+   Note that multiple AutoFDO profile files can be merged into one via::
+
+      $ llvm-profdata merge -o <profile_file> <profile_1> <profile_2> ... <profile_n>
+
+6) Rebuild the kernel using the AutoFDO profile file with the same config as step 1,
+   (Note CONFIG_AUTOFDO_CLANG needs to be enabled)::
+
+      $ make LLVM=1 CLANG_AUTOFDO_PROFILE=<profile_file>
diff --git a/Documentation/dev-tools/index.rst b/Documentation/dev-tools/index.rst
index 53d4d124f9c52..6945644f7008a 100644
--- a/Documentation/dev-tools/index.rst
+++ b/Documentation/dev-tools/index.rst
@@ -34,6 +34,7 @@ Documentation/dev-tools/testing-overview.rst
    ktap
    checkuapi
    gpio-sloppy-logic-analyzer
+   autofdo
 
 
 .. only::  subproject and html
diff --git a/MAINTAINERS b/MAINTAINERS
index a274079502426..d6ea49433747a 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -3665,6 +3665,13 @@ F:	kernel/audit*
 F:	lib/*audit.c
 K:	\baudit_[a-z_0-9]\+\b
 
+AUTOFDO BUILD
+M:	Rong Xu <xur@google.com>
+M:	Han Shen <shenhan@google.com>
+S:	Supported
+F:	Documentation/dev-tools/autofdo.rst
+F:	scripts/Makefile.autofdo
+
 AUXILIARY BUS DRIVER
 M:	Greg Kroah-Hartman <gregkh@linuxfoundation.org>
 R:	Dave Ertman <david.m.ertman@intel.com>
diff --git a/Makefile b/Makefile
index 5e04e4abffd88..b89d87b5dca79 100644
--- a/Makefile
+++ b/Makefile
@@ -1018,6 +1018,7 @@ include-$(CONFIG_KMSAN)		+= scripts/Makefile.kmsan
 include-$(CONFIG_UBSAN)		+= scripts/Makefile.ubsan
 include-$(CONFIG_KCOV)		+= scripts/Makefile.kcov
 include-$(CONFIG_RANDSTRUCT)	+= scripts/Makefile.randstruct
+include-$(CONFIG_AUTOFDO_CLANG)	+= scripts/Makefile.autofdo
 include-$(CONFIG_GCC_PLUGINS)	+= scripts/Makefile.gcc-plugins
 
 include $(addprefix $(srctree)/, $(include-y))
diff --git a/arch/Kconfig b/arch/Kconfig
index bd9f095d69fa0..8dca3b5e6ef53 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -811,6 +811,26 @@ config LTO_CLANG_THIN
 	  If unsure, say Y.
 endchoice
 
+config ARCH_SUPPORTS_AUTOFDO_CLANG
+	bool
+
+config AUTOFDO_CLANG
+	bool "Enable Clang's AutoFDO build (EXPERIMENTAL)"
+	depends on ARCH_SUPPORTS_AUTOFDO_CLANG
+	depends on CC_IS_CLANG && CLANG_VERSION >= 170000
+	help
+	  This option enables Clang’s AutoFDO build. When
+	  an AutoFDO profile is specified in variable
+	  CLANG_AUTOFDO_PROFILE during the build process,
+	  Clang uses the profile to optimize the kernel.
+
+	  If no profile is specified, AutoFDO options are
+	  still passed to Clang to facilitate the collection
+	  of perf data for creating an AutoFDO profile in
+	  subsequent builds.
+
+	  If unsure, say N.
+
 config ARCH_SUPPORTS_CFI_CLANG
 	bool
 	help
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 16354dfa6d965..9dc87661fb373 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -126,6 +126,7 @@ config X86
 	select ARCH_SUPPORTS_LTO_CLANG
 	select ARCH_SUPPORTS_LTO_CLANG_THIN
 	select ARCH_SUPPORTS_RT
+	select ARCH_SUPPORTS_AUTOFDO_CLANG
 	select ARCH_USE_BUILTIN_BSWAP
 	select ARCH_USE_CMPXCHG_LOCKREF		if X86_CMPXCHG64
 	select ARCH_USE_MEMTEST
diff --git a/scripts/Makefile.autofdo b/scripts/Makefile.autofdo
new file mode 100644
index 0000000000000..ff96a63fea7cd
--- /dev/null
+++ b/scripts/Makefile.autofdo
@@ -0,0 +1,22 @@
+# SPDX-License-Identifier: GPL-2.0
+
+# Enable available and selected Clang AutoFDO features.
+
+CFLAGS_AUTOFDO_CLANG := -fdebug-info-for-profiling -mllvm -enable-fs-discriminator=true -mllvm -improved-fs-discriminator=true
+
+ifndef CONFIG_DEBUG_INFO
+  CFLAGS_AUTOFDO_CLANG += -gmlt
+endif
+
+ifdef CLANG_AUTOFDO_PROFILE
+  CFLAGS_AUTOFDO_CLANG += -fprofile-sample-use=$(CLANG_AUTOFDO_PROFILE)
+endif
+
+ifdef CONFIG_LTO_CLANG_THIN
+  ifdef CLANG_AUTOFDO_PROFILE
+    KBUILD_LDFLAGS += --lto-sample-profile=$(CLANG_AUTOFDO_PROFILE)
+  endif
+  KBUILD_LDFLAGS += --mllvm=-enable-fs-discriminator=true --mllvm=-improved-fs-discriminator=true -plugin-opt=thinlto
+endif
+
+export CFLAGS_AUTOFDO_CLANG
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index 01a9f567d5af4..2d0942c1a0277 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -191,6 +191,16 @@ _c_flags += $(if $(patsubst n%,, \
 	-D__KCSAN_INSTRUMENT_BARRIERS__)
 endif
 
+#
+# Enable AutoFDO build flags except some files or directories we don't want to
+# enable (depends on variables AUTOFDO_PROFILE_obj.o and AUTOFDO_PROFILE).
+#
+ifeq ($(CONFIG_AUTOFDO_CLANG),y)
+_c_flags += $(if $(patsubst n%,, \
+	$(AUTOFDO_PROFILE_$(target-stem).o)$(AUTOFDO_PROFILE)$(is-kernel-object)), \
+	$(CFLAGS_AUTOFDO_CLANG))
+endif
+
 # $(src) for including checkin headers from generated source files
 # $(obj) for including generated headers from checkin source files
 ifeq ($(KBUILD_EXTMOD),)
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 6604f5d038aad..4c5229991e1e0 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -4557,6 +4557,7 @@ static int validate_ibt(struct objtool_file *file)
 		    !strcmp(sec->name, "__jump_table")			||
 		    !strcmp(sec->name, "__mcount_loc")			||
 		    !strcmp(sec->name, ".kcfi_traps")			||
+		    !strcmp(sec->name, ".llvm.call-graph-profile")	||
 		    strstr(sec->name, "__patchable_function_entries"))
 			continue;
 
-- 
2.47.0.163.g1226f6d8fa-goog

Re: [PATCH v7 1/7] Add AutoFDO support for Clang build

Posted by Peter Jung 3 weeks, 1 day ago


On 02.11.24 18:51, Rong Xu wrote:
> Add the build support for using Clang's AutoFDO. Building the kernel
> with AutoFDO does not reduce the optimization level from the
> compiler. AutoFDO uses hardware sampling to gather information about
> the frequency of execution of different code paths within a binary.
> This information is then used to guide the compiler's optimization
> decisions, resulting in a more efficient binary. Experiments
> showed that the kernel can improve up to 10% in latency.
> 
> The support requires a Clang compiler after LLVM 17. This submission
> is limited to x86 platforms that support PMU features like LBR on
> Intel machines and AMD Zen3 BRS. Support for SPE on ARM 1,
>   and BRBE on ARM 1 is part of planned future work.
> 
> Here is an example workflow for AutoFDO kernel:
> 
> 1) Build the kernel on the host machine with LLVM enabled, for example,
>         $ make menuconfig LLVM=1
>      Turn on AutoFDO build config:
>        CONFIG_AUTOFDO_CLANG=y
>      With a configuration that has LLVM enabled, use the following
>      command:
>         scripts/config -e AUTOFDO_CLANG
>      After getting the config, build with
>        $ make LLVM=1
> 
> 2) Install the kernel on the test machine.
> 
> 3) Run the load tests. The '-c' option in perf specifies the sample
>     event period. We suggest     using a suitable prime number,
>     like 500009, for this purpose.
>     For Intel platforms:
>        $ perf record -e BR_INST_RETIRED.NEAR_TAKEN:k -a -N -b -c <count> \
>          -o <perf_file> -- <loadtest>
>     For AMD platforms:
>        The supported system are: Zen3 with BRS, or Zen4 with amd_lbr_v2
>       For Zen3:
>        $ cat proc/cpuinfo | grep " brs"
>        For Zen4:
>        $ cat proc/cpuinfo | grep amd_lbr_v2
>        $ perf record --pfm-events RETIRED_TAKEN_BRANCH_INSTRUCTIONS:k -a \
>          -N -b -c <count> -o <perf_file> -- <loadtest>
> 
> 4) (Optional) Download the raw perf file to the host machine.
> 
> 5) To generate an AutoFDO profile, two offline tools are available:
>     create_llvm_prof and llvm_profgen. The create_llvm_prof tool is part
>     of the AutoFDO project and can be found on GitHub
>     (https://github.com/google/autofdo), version v0.30.1 or later. The
>     llvm_profgen tool is included in the LLVM compiler itself. It's
>     important to note that the version of llvm_profgen doesn't need to
>     match the version of Clang. It needs to be the LLVM 19 release or
>     later, or from the LLVM trunk.
>        $ llvm-profgen --kernel --binary=<vmlinux> --perfdata=<perf_file> \
>          -o <profile_file>
>     or
>        $ create_llvm_prof --binary=<vmlinux> --profile=<perf_file> \
>          --format=extbinary --out=<profile_file>
> 
>     Note that multiple AutoFDO profile files can be merged into one via:
>        $ llvm-profdata merge -o <profile_file>  <profile_1> ... <profile_n>
> 
> 6) Rebuild the kernel using the AutoFDO profile file with the same config
>     as step 1, (Note CONFIG_AUTOFDO_CLANG needs to be enabled):
>        $ make LLVM=1 CLANG_AUTOFDO_PROFILE=<profile_file>
> 
> Co-developed-by: Han Shen<shenhan@google.com>
> Signed-off-by: Han Shen<shenhan@google.com>
> Signed-off-by: Rong Xu<xur@google.com>
> Suggested-by: Sriraman Tallam<tmsriram@google.com>
> Suggested-by: Krzysztof Pszeniczny<kpszeniczny@google.com>
> Suggested-by: Nick Desaulniers<ndesaulniers@google.com>
> Suggested-by: Stephane Eranian<eranian@google.com>
> Tested-by: Yonghong Song<yonghong.song@linux.dev>
> Tested-by: Yabin Cui<yabinc@google.com>
> Tested-by: Nathan Chancellor<nathan@kernel.org>
> Reviewed-by: Kees Cook<kees@kernel.org>

Tested-by: Peter Jung <ptr1337@cachyos.org>

Re: [PATCH v7 1/7] Add AutoFDO support for Clang build

Posted by Peter Jung 3 weeks, 1 day ago


On 02.11.24 20:46, Peter Jung wrote:
> 
> 
> On 02.11.24 18:51, Rong Xu wrote:
>> Add the build support for using Clang's AutoFDO. Building the kernel
>> with AutoFDO does not reduce the optimization level from the
>> compiler. AutoFDO uses hardware sampling to gather information about
>> the frequency of execution of different code paths within a binary.
>> This information is then used to guide the compiler's optimization
>> decisions, resulting in a more efficient binary. Experiments
>> showed that the kernel can improve up to 10% in latency.
>>
>> The support requires a Clang compiler after LLVM 17. This submission
>> is limited to x86 platforms that support PMU features like LBR on
>> Intel machines and AMD Zen3 BRS. Support for SPE on ARM 1,
>>   and BRBE on ARM 1 is part of planned future work.
>>
>> Here is an example workflow for AutoFDO kernel:
>>
>> 1) Build the kernel on the host machine with LLVM enabled, for example,
>>         $ make menuconfig LLVM=1
>>      Turn on AutoFDO build config:
>>        CONFIG_AUTOFDO_CLANG=y
>>      With a configuration that has LLVM enabled, use the following
>>      command:
>>         scripts/config -e AUTOFDO_CLANG
>>      After getting the config, build with
>>        $ make LLVM=1
>>
>> 2) Install the kernel on the test machine.
>>
>> 3) Run the load tests. The '-c' option in perf specifies the sample
>>     event period. We suggest     using a suitable prime number,
>>     like 500009, for this purpose.
>>     For Intel platforms:
>>        $ perf record -e BR_INST_RETIRED.NEAR_TAKEN:k -a -N -b -c 
>> <count> \
>>          -o <perf_file> -- <loadtest>
>>     For AMD platforms:
>>        The supported system are: Zen3 with BRS, or Zen4 with amd_lbr_v2
>>       For Zen3:
>>        $ cat proc/cpuinfo | grep " brs"
>>        For Zen4:
>>        $ cat proc/cpuinfo | grep amd_lbr_v2
>>        $ perf record --pfm-events RETIRED_TAKEN_BRANCH_INSTRUCTIONS:k 
>> -a \
>>          -N -b -c <count> -o <perf_file> -- <loadtest>
>>
>> 4) (Optional) Download the raw perf file to the host machine.
>>
>> 5) To generate an AutoFDO profile, two offline tools are available:
>>     create_llvm_prof and llvm_profgen. The create_llvm_prof tool is part
>>     of the AutoFDO project and can be found on GitHub
>>     (https://github.com/google/autofdo), version v0.30.1 or later. The
>>     llvm_profgen tool is included in the LLVM compiler itself. It's
>>     important to note that the version of llvm_profgen doesn't need to
>>     match the version of Clang. It needs to be the LLVM 19 release or
>>     later, or from the LLVM trunk.
>>        $ llvm-profgen --kernel --binary=<vmlinux> -- 
>> perfdata=<perf_file> \
>>          -o <profile_file>
>>     or
>>        $ create_llvm_prof --binary=<vmlinux> --profile=<perf_file> \
>>          --format=extbinary --out=<profile_file>
>>
>>     Note that multiple AutoFDO profile files can be merged into one via:
>>        $ llvm-profdata merge -o <profile_file>  <profile_1> ... 
>> <profile_n>
>>
>> 6) Rebuild the kernel using the AutoFDO profile file with the same config
>>     as step 1, (Note CONFIG_AUTOFDO_CLANG needs to be enabled):
>>        $ make LLVM=1 CLANG_AUTOFDO_PROFILE=<profile_file>
>>
>> Co-developed-by: Han Shen<shenhan@google.com>
>> Signed-off-by: Han Shen<shenhan@google.com>
>> Signed-off-by: Rong Xu<xur@google.com>
>> Suggested-by: Sriraman Tallam<tmsriram@google.com>
>> Suggested-by: Krzysztof Pszeniczny<kpszeniczny@google.com>
>> Suggested-by: Nick Desaulniers<ndesaulniers@google.com>
>> Suggested-by: Stephane Eranian<eranian@google.com>
>> Tested-by: Yonghong Song<yonghong.song@linux.dev>
>> Tested-by: Yabin Cui<yabinc@google.com>
>> Tested-by: Nathan Chancellor<nathan@kernel.org>
>> Reviewed-by: Kees Cook<kees@kernel.org>
> 
> Tested-by: Peter Jung <ptr1337@cachyos.org>
> 

The compilations and testing with the "make pacman-pkg" function from 
the kernel worked fine.

One problem I do face:
When I apply a AutoFDO profile together with the PKGBUILD [1] from 
archlinux im running into issues at "module_install" at the packaging.

See following log:
```
make[2]: *** [scripts/Makefile.modinst:125: 
/tmp/makepkg/linux-cachyos-rc-autofdo/pkg/linux-cachyos-rc-autofdo/usr/lib/modules/6.12.0-rc5-5-cachyos-rc-autofdo/kernel/arch/x86/kvm/kvm.ko] 
Error 1
make[2]: *** Deleting file 
'/tmp/makepkg/linux-cachyos-rc-autofdo/pkg/linux-cachyos-rc-autofdo/usr/lib/modules/6.12.0-rc5-5-cachyos-rc-autofdo/kernel/arch/x86/kvm/kvm.ko'
   INSTALL 
/tmp/makepkg/linux-cachyos-rc-autofdo/pkg/linux-cachyos-rc-autofdo/usr/lib/modules/6.12.0-rc5-5-cachyos-rc-autofdo/kernel/crypto/cryptd.ko
make[2]: *** Waiting for unfinished jobs....
```


This can be fixed with removed "INSTALL_MOD_STRIP=1" to the passed 
parameters of module_install.

This explicitly only happens, if a profile is passed - otherwise the 
packaging works without problems.

Regards,

Peter Jung

Re: [PATCH v7 1/7] Add AutoFDO support for Clang build

Posted by Han Shen 2 weeks, 6 days ago

Hi Peter, thanks for reporting the issue. I am trying to reproduce it
in the up-to-date archlinux environment. Below is what I have:
  0. pacman -Syu
  1. cloned archlinux build files from
https://aur.archlinux.org/linux-mainline.git the newest mainline
version is 6.12rc5-1.
  2. changed the PKGBUILD file to include the patches series
  3. changed the "config" to turn on clang autofdo
  4. collected afdo profiles
  5. MAKEFLAGS="-j48 V=1 LLVM=1 CLANG_AUTOFDO_PROFILE=$(pwd)/perf.afdo" \
        makepkg -s --skipinteg --skippgp
  6. install and reboot
The above steps succeeded.
You mentioned the error happens at "module_install", can you instruct
me how to execute the "module_install" step?

Thanks,
Han

On Sat, Nov 2, 2024 at 12:53 PM Peter Jung <ptr1337@cachyos.org> wrote:
>
>
>
> On 02.11.24 20:46, Peter Jung wrote:
> >
> >
> > On 02.11.24 18:51, Rong Xu wrote:
> >> Add the build support for using Clang's AutoFDO. Building the kernel
> >> with AutoFDO does not reduce the optimization level from the
> >> compiler. AutoFDO uses hardware sampling to gather information about
> >> the frequency of execution of different code paths within a binary.
> >> This information is then used to guide the compiler's optimization
> >> decisions, resulting in a more efficient binary. Experiments
> >> showed that the kernel can improve up to 10% in latency.
> >>
> >> The support requires a Clang compiler after LLVM 17. This submission
> >> is limited to x86 platforms that support PMU features like LBR on
> >> Intel machines and AMD Zen3 BRS. Support for SPE on ARM 1,
> >>   and BRBE on ARM 1 is part of planned future work.
> >>
> >> Here is an example workflow for AutoFDO kernel:
> >>
> >> 1) Build the kernel on the host machine with LLVM enabled, for example,
> >>         $ make menuconfig LLVM=1
> >>      Turn on AutoFDO build config:
> >>        CONFIG_AUTOFDO_CLANG=y
> >>      With a configuration that has LLVM enabled, use the following
> >>      command:
> >>         scripts/config -e AUTOFDO_CLANG
> >>      After getting the config, build with
> >>        $ make LLVM=1
> >>
> >> 2) Install the kernel on the test machine.
> >>
> >> 3) Run the load tests. The '-c' option in perf specifies the sample
> >>     event period. We suggest     using a suitable prime number,
> >>     like 500009, for this purpose.
> >>     For Intel platforms:
> >>        $ perf record -e BR_INST_RETIRED.NEAR_TAKEN:k -a -N -b -c
> >> <count> \
> >>          -o <perf_file> -- <loadtest>
> >>     For AMD platforms:
> >>        The supported system are: Zen3 with BRS, or Zen4 with amd_lbr_v2
> >>       For Zen3:
> >>        $ cat proc/cpuinfo | grep " brs"
> >>        For Zen4:
> >>        $ cat proc/cpuinfo | grep amd_lbr_v2
> >>        $ perf record --pfm-events RETIRED_TAKEN_BRANCH_INSTRUCTIONS:k
> >> -a \
> >>          -N -b -c <count> -o <perf_file> -- <loadtest>
> >>
> >> 4) (Optional) Download the raw perf file to the host machine.
> >>
> >> 5) To generate an AutoFDO profile, two offline tools are available:
> >>     create_llvm_prof and llvm_profgen. The create_llvm_prof tool is part
> >>     of the AutoFDO project and can be found on GitHub
> >>     (https://github.com/google/autofdo), version v0.30.1 or later. The
> >>     llvm_profgen tool is included in the LLVM compiler itself. It's
> >>     important to note that the version of llvm_profgen doesn't need to
> >>     match the version of Clang. It needs to be the LLVM 19 release or
> >>     later, or from the LLVM trunk.
> >>        $ llvm-profgen --kernel --binary=<vmlinux> --
> >> perfdata=<perf_file> \
> >>          -o <profile_file>
> >>     or
> >>        $ create_llvm_prof --binary=<vmlinux> --profile=<perf_file> \
> >>          --format=extbinary --out=<profile_file>
> >>
> >>     Note that multiple AutoFDO profile files can be merged into one via:
> >>        $ llvm-profdata merge -o <profile_file>  <profile_1> ...
> >> <profile_n>
> >>
> >> 6) Rebuild the kernel using the AutoFDO profile file with the same config
> >>     as step 1, (Note CONFIG_AUTOFDO_CLANG needs to be enabled):
> >>        $ make LLVM=1 CLANG_AUTOFDO_PROFILE=<profile_file>
> >>
> >> Co-developed-by: Han Shen<shenhan@google.com>
> >> Signed-off-by: Han Shen<shenhan@google.com>
> >> Signed-off-by: Rong Xu<xur@google.com>
> >> Suggested-by: Sriraman Tallam<tmsriram@google.com>
> >> Suggested-by: Krzysztof Pszeniczny<kpszeniczny@google.com>
> >> Suggested-by: Nick Desaulniers<ndesaulniers@google.com>
> >> Suggested-by: Stephane Eranian<eranian@google.com>
> >> Tested-by: Yonghong Song<yonghong.song@linux.dev>
> >> Tested-by: Yabin Cui<yabinc@google.com>
> >> Tested-by: Nathan Chancellor<nathan@kernel.org>
> >> Reviewed-by: Kees Cook<kees@kernel.org>
> >
> > Tested-by: Peter Jung <ptr1337@cachyos.org>
> >
>
> The compilations and testing with the "make pacman-pkg" function from
> the kernel worked fine.
>
> One problem I do face:
> When I apply a AutoFDO profile together with the PKGBUILD [1] from
> archlinux im running into issues at "module_install" at the packaging.
>
> See following log:
> ```
> make[2]: *** [scripts/Makefile.modinst:125:
> /tmp/makepkg/linux-cachyos-rc-autofdo/pkg/linux-cachyos-rc-autofdo/usr/lib/modules/6.12.0-rc5-5-cachyos-rc-autofdo/kernel/arch/x86/kvm/kvm.ko]
> Error 1
> make[2]: *** Deleting file
> '/tmp/makepkg/linux-cachyos-rc-autofdo/pkg/linux-cachyos-rc-autofdo/usr/lib/modules/6.12.0-rc5-5-cachyos-rc-autofdo/kernel/arch/x86/kvm/kvm.ko'
>    INSTALL
> /tmp/makepkg/linux-cachyos-rc-autofdo/pkg/linux-cachyos-rc-autofdo/usr/lib/modules/6.12.0-rc5-5-cachyos-rc-autofdo/kernel/crypto/cryptd.ko
> make[2]: *** Waiting for unfinished jobs....
> ```
>
>
> This can be fixed with removed "INSTALL_MOD_STRIP=1" to the passed
> parameters of module_install.
>
> This explicitly only happens, if a profile is passed - otherwise the
> packaging works without problems.
>
> Regards,
>
> Peter Jung
>

Re: [PATCH v7 1/7] Add AutoFDO support for Clang build

Posted by Peter Jung 2 weeks, 6 days ago

Hi Han,

I have tested your provided method, but the AutoFDO profile (lld does 
not get lto-sample-profile=$pathtoprofile passed)  nor Clang as compiler 
gets used.
Please replace following PKGBUILD and config from linux-mainline with 
the provided one in the gist. The patch is also included there.

https://gist.github.com/ptr1337/c92728bb273f7dbc2817db75eedec9ed

The main change I am doing here, is passing following to the build array 
and replacing "make all":

make LLVM=1 LLVM_IAS=1 CLANG_AUTOFDO_PROFILE=${srcdir}/perf.afdo all

When compiling the kernel with makepkg, this results at the packaging to 
following issue and can be reliable reproduced.

Regards,

Peter


On 04.11.24 05:50, Han Shen wrote:
> Hi Peter, thanks for reporting the issue. I am trying to reproduce it
> in the up-to-date archlinux environment. Below is what I have:
>    0. pacman -Syu
>    1. cloned archlinux build files from
> https://aur.archlinux.org/linux-mainline.git the newest mainline
> version is 6.12rc5-1.
>    2. changed the PKGBUILD file to include the patches series
>    3. changed the "config" to turn on clang autofdo
>    4. collected afdo profiles
>    5. MAKEFLAGS="-j48 V=1 LLVM=1 CLANG_AUTOFDO_PROFILE=$(pwd)/perf.afdo" \
>          makepkg -s --skipinteg --skippgp
>    6. install and reboot
> The above steps succeeded.
> You mentioned the error happens at "module_install", can you instruct
> me how to execute the "module_install" step?
> 
> Thanks,
> Han
> 
> On Sat, Nov 2, 2024 at 12:53 PM Peter Jung<ptr1337@cachyos.org> wrote:
>>
>>
>> On 02.11.24 20:46, Peter Jung wrote:
>>>
>>> On 02.11.24 18:51, Rong Xu wrote:
>>>> Add the build support for using Clang's AutoFDO. Building the kernel
>>>> with AutoFDO does not reduce the optimization level from the
>>>> compiler. AutoFDO uses hardware sampling to gather information about
>>>> the frequency of execution of different code paths within a binary.
>>>> This information is then used to guide the compiler's optimization
>>>> decisions, resulting in a more efficient binary. Experiments
>>>> showed that the kernel can improve up to 10% in latency.
>>>>
>>>> The support requires a Clang compiler after LLVM 17. This submission
>>>> is limited to x86 platforms that support PMU features like LBR on
>>>> Intel machines and AMD Zen3 BRS. Support for SPE on ARM 1,
>>>>    and BRBE on ARM 1 is part of planned future work.
>>>>
>>>> Here is an example workflow for AutoFDO kernel:
>>>>
>>>> 1) Build the kernel on the host machine with LLVM enabled, for example,
>>>>          $ make menuconfig LLVM=1
>>>>       Turn on AutoFDO build config:
>>>>         CONFIG_AUTOFDO_CLANG=y
>>>>       With a configuration that has LLVM enabled, use the following
>>>>       command:
>>>>          scripts/config -e AUTOFDO_CLANG
>>>>       After getting the config, build with
>>>>         $ make LLVM=1
>>>>
>>>> 2) Install the kernel on the test machine.
>>>>
>>>> 3) Run the load tests. The '-c' option in perf specifies the sample
>>>>      event period. We suggest     using a suitable prime number,
>>>>      like 500009, for this purpose.
>>>>      For Intel platforms:
>>>>         $ perf record -e BR_INST_RETIRED.NEAR_TAKEN:k -a -N -b -c
>>>> <count> \
>>>>           -o <perf_file> -- <loadtest>
>>>>      For AMD platforms:
>>>>         The supported system are: Zen3 with BRS, or Zen4 with amd_lbr_v2
>>>>        For Zen3:
>>>>         $ cat proc/cpuinfo | grep " brs"
>>>>         For Zen4:
>>>>         $ cat proc/cpuinfo | grep amd_lbr_v2
>>>>         $ perf record --pfm-events RETIRED_TAKEN_BRANCH_INSTRUCTIONS:k
>>>> -a \
>>>>           -N -b -c <count> -o <perf_file> -- <loadtest>
>>>>
>>>> 4) (Optional) Download the raw perf file to the host machine.
>>>>
>>>> 5) To generate an AutoFDO profile, two offline tools are available:
>>>>      create_llvm_prof and llvm_profgen. The create_llvm_prof tool is part
>>>>      of the AutoFDO project and can be found on GitHub
>>>>      (https://github.com/google/autofdo), version v0.30.1 or later. The
>>>>      llvm_profgen tool is included in the LLVM compiler itself. It's
>>>>      important to note that the version of llvm_profgen doesn't need to
>>>>      match the version of Clang. It needs to be the LLVM 19 release or
>>>>      later, or from the LLVM trunk.
>>>>         $ llvm-profgen --kernel --binary=<vmlinux> --
>>>> perfdata=<perf_file> \
>>>>           -o <profile_file>
>>>>      or
>>>>         $ create_llvm_prof --binary=<vmlinux> --profile=<perf_file> \
>>>>           --format=extbinary --out=<profile_file>
>>>>
>>>>      Note that multiple AutoFDO profile files can be merged into one via:
>>>>         $ llvm-profdata merge -o <profile_file>  <profile_1> ...
>>>> <profile_n>
>>>>
>>>> 6) Rebuild the kernel using the AutoFDO profile file with the same config
>>>>      as step 1, (Note CONFIG_AUTOFDO_CLANG needs to be enabled):
>>>>         $ make LLVM=1 CLANG_AUTOFDO_PROFILE=<profile_file>
>>>>
>>>> Co-developed-by: Han Shen<shenhan@google.com>
>>>> Signed-off-by: Han Shen<shenhan@google.com>
>>>> Signed-off-by: Rong Xu<xur@google.com>
>>>> Suggested-by: Sriraman Tallam<tmsriram@google.com>
>>>> Suggested-by: Krzysztof Pszeniczny<kpszeniczny@google.com>
>>>> Suggested-by: Nick Desaulniers<ndesaulniers@google.com>
>>>> Suggested-by: Stephane Eranian<eranian@google.com>
>>>> Tested-by: Yonghong Song<yonghong.song@linux.dev>
>>>> Tested-by: Yabin Cui<yabinc@google.com>
>>>> Tested-by: Nathan Chancellor<nathan@kernel.org>
>>>> Reviewed-by: Kees Cook<kees@kernel.org>
>>> Tested-by: Peter Jung<ptr1337@cachyos.org>
>>>
>> The compilations and testing with the "make pacman-pkg" function from
>> the kernel worked fine.
>>
>> One problem I do face:
>> When I apply a AutoFDO profile together with the PKGBUILD [1] from
>> archlinux im running into issues at "module_install" at the packaging.
>>
>> See following log:
>> ```
>> make[2]: *** [scripts/Makefile.modinst:125:
>> /tmp/makepkg/linux-cachyos-rc-autofdo/pkg/linux-cachyos-rc-autofdo/usr/lib/modules/6.12.0-rc5-5-cachyos-rc-autofdo/kernel/arch/x86/kvm/kvm.ko]
>> Error 1
>> make[2]: *** Deleting file
>> '/tmp/makepkg/linux-cachyos-rc-autofdo/pkg/linux-cachyos-rc-autofdo/usr/lib/modules/6.12.0-rc5-5-cachyos-rc-autofdo/kernel/arch/x86/kvm/kvm.ko'
>>     INSTALL
>> /tmp/makepkg/linux-cachyos-rc-autofdo/pkg/linux-cachyos-rc-autofdo/usr/lib/modules/6.12.0-rc5-5-cachyos-rc-autofdo/kernel/crypto/cryptd.ko
>> make[2]: *** Waiting for unfinished jobs....
>> ```
>>
>>
>> This can be fixed with removed "INSTALL_MOD_STRIP=1" to the passed
>> parameters of module_install.
>>
>> This explicitly only happens, if a profile is passed - otherwise the
>> packaging works without problems.
>>
>> Regards,
>>
>> Peter Jung
>>

Re: [PATCH v7 1/7] Add AutoFDO support for Clang build

Posted by Han Shen 2 weeks, 5 days ago

Hi Peter,
Thanks for providing the detailed reproduce.
Now I can see the error (after I synced to 6.12.0-rc6, I was using rc5).
I'll look into that and report back.

> I have tested your provided method, but the AutoFDO profile (lld does
not get lto-sample-profile=$pathtoprofile passed)

I see. You also turned on ThinLTO, which I didn't, so the profile was
only used during compilation, not passed to lld.

Thanks,
Han

On Mon, Nov 4, 2024 at 9:31 AM Peter Jung <ptr1337@cachyos.org> wrote:
>
> Hi Han,
>
> I have tested your provided method, but the AutoFDO profile (lld does
> not get lto-sample-profile=$pathtoprofile passed)  nor Clang as compiler
> gets used.
> Please replace following PKGBUILD and config from linux-mainline with
> the provided one in the gist. The patch is also included there.
>
> https://gist.github.com/ptr1337/c92728bb273f7dbc2817db75eedec9ed
>
> The main change I am doing here, is passing following to the build array
> and replacing "make all":
>
> make LLVM=1 LLVM_IAS=1 CLANG_AUTOFDO_PROFILE=${srcdir}/perf.afdo all
>
> When compiling the kernel with makepkg, this results at the packaging to
> following issue and can be reliable reproduced.
>
> Regards,
>
> Peter
>
>
> On 04.11.24 05:50, Han Shen wrote:
> > Hi Peter, thanks for reporting the issue. I am trying to reproduce it
> > in the up-to-date archlinux environment. Below is what I have:
> >    0. pacman -Syu
> >    1. cloned archlinux build files from
> > https://aur.archlinux.org/linux-mainline.git the newest mainline
> > version is 6.12rc5-1.
> >    2. changed the PKGBUILD file to include the patches series
> >    3. changed the "config" to turn on clang autofdo
> >    4. collected afdo profiles
> >    5. MAKEFLAGS="-j48 V=1 LLVM=1 CLANG_AUTOFDO_PROFILE=$(pwd)/perf.afdo" \
> >          makepkg -s --skipinteg --skippgp
> >    6. install and reboot
> > The above steps succeeded.
> > You mentioned the error happens at "module_install", can you instruct
> > me how to execute the "module_install" step?
> >
> > Thanks,
> > Han
> >
> > On Sat, Nov 2, 2024 at 12:53 PM Peter Jung<ptr1337@cachyos.org> wrote:
> >>
> >>
> >> On 02.11.24 20:46, Peter Jung wrote:
> >>>
> >>> On 02.11.24 18:51, Rong Xu wrote:
> >>>> Add the build support for using Clang's AutoFDO. Building the kernel
> >>>> with AutoFDO does not reduce the optimization level from the
> >>>> compiler. AutoFDO uses hardware sampling to gather information about
> >>>> the frequency of execution of different code paths within a binary.
> >>>> This information is then used to guide the compiler's optimization
> >>>> decisions, resulting in a more efficient binary. Experiments
> >>>> showed that the kernel can improve up to 10% in latency.
> >>>>
> >>>> The support requires a Clang compiler after LLVM 17. This submission
> >>>> is limited to x86 platforms that support PMU features like LBR on
> >>>> Intel machines and AMD Zen3 BRS. Support for SPE on ARM 1,
> >>>>    and BRBE on ARM 1 is part of planned future work.
> >>>>
> >>>> Here is an example workflow for AutoFDO kernel:
> >>>>
> >>>> 1) Build the kernel on the host machine with LLVM enabled, for example,
> >>>>          $ make menuconfig LLVM=1
> >>>>       Turn on AutoFDO build config:
> >>>>         CONFIG_AUTOFDO_CLANG=y
> >>>>       With a configuration that has LLVM enabled, use the following
> >>>>       command:
> >>>>          scripts/config -e AUTOFDO_CLANG
> >>>>       After getting the config, build with
> >>>>         $ make LLVM=1
> >>>>
> >>>> 2) Install the kernel on the test machine.
> >>>>
> >>>> 3) Run the load tests. The '-c' option in perf specifies the sample
> >>>>      event period. We suggest     using a suitable prime number,
> >>>>      like 500009, for this purpose.
> >>>>      For Intel platforms:
> >>>>         $ perf record -e BR_INST_RETIRED.NEAR_TAKEN:k -a -N -b -c
> >>>> <count> \
> >>>>           -o <perf_file> -- <loadtest>
> >>>>      For AMD platforms:
> >>>>         The supported system are: Zen3 with BRS, or Zen4 with amd_lbr_v2
> >>>>        For Zen3:
> >>>>         $ cat proc/cpuinfo | grep " brs"
> >>>>         For Zen4:
> >>>>         $ cat proc/cpuinfo | grep amd_lbr_v2
> >>>>         $ perf record --pfm-events RETIRED_TAKEN_BRANCH_INSTRUCTIONS:k
> >>>> -a \
> >>>>           -N -b -c <count> -o <perf_file> -- <loadtest>
> >>>>
> >>>> 4) (Optional) Download the raw perf file to the host machine.
> >>>>
> >>>> 5) To generate an AutoFDO profile, two offline tools are available:
> >>>>      create_llvm_prof and llvm_profgen. The create_llvm_prof tool is part
> >>>>      of the AutoFDO project and can be found on GitHub
> >>>>      (https://github.com/google/autofdo), version v0.30.1 or later. The
> >>>>      llvm_profgen tool is included in the LLVM compiler itself. It's
> >>>>      important to note that the version of llvm_profgen doesn't need to
> >>>>      match the version of Clang. It needs to be the LLVM 19 release or
> >>>>      later, or from the LLVM trunk.
> >>>>         $ llvm-profgen --kernel --binary=<vmlinux> --
> >>>> perfdata=<perf_file> \
> >>>>           -o <profile_file>
> >>>>      or
> >>>>         $ create_llvm_prof --binary=<vmlinux> --profile=<perf_file> \
> >>>>           --format=extbinary --out=<profile_file>
> >>>>
> >>>>      Note that multiple AutoFDO profile files can be merged into one via:
> >>>>         $ llvm-profdata merge -o <profile_file>  <profile_1> ...
> >>>> <profile_n>
> >>>>
> >>>> 6) Rebuild the kernel using the AutoFDO profile file with the same config
> >>>>      as step 1, (Note CONFIG_AUTOFDO_CLANG needs to be enabled):
> >>>>         $ make LLVM=1 CLANG_AUTOFDO_PROFILE=<profile_file>
> >>>>
> >>>> Co-developed-by: Han Shen<shenhan@google.com>
> >>>> Signed-off-by: Han Shen<shenhan@google.com>
> >>>> Signed-off-by: Rong Xu<xur@google.com>
> >>>> Suggested-by: Sriraman Tallam<tmsriram@google.com>
> >>>> Suggested-by: Krzysztof Pszeniczny<kpszeniczny@google.com>
> >>>> Suggested-by: Nick Desaulniers<ndesaulniers@google.com>
> >>>> Suggested-by: Stephane Eranian<eranian@google.com>
> >>>> Tested-by: Yonghong Song<yonghong.song@linux.dev>
> >>>> Tested-by: Yabin Cui<yabinc@google.com>
> >>>> Tested-by: Nathan Chancellor<nathan@kernel.org>
> >>>> Reviewed-by: Kees Cook<kees@kernel.org>
> >>> Tested-by: Peter Jung<ptr1337@cachyos.org>
> >>>
> >> The compilations and testing with the "make pacman-pkg" function from
> >> the kernel worked fine.
> >>
> >> One problem I do face:
> >> When I apply a AutoFDO profile together with the PKGBUILD [1] from
> >> archlinux im running into issues at "module_install" at the packaging.
> >>
> >> See following log:
> >> ```
> >> make[2]: *** [scripts/Makefile.modinst:125:
> >> /tmp/makepkg/linux-cachyos-rc-autofdo/pkg/linux-cachyos-rc-autofdo/usr/lib/modules/6.12.0-rc5-5-cachyos-rc-autofdo/kernel/arch/x86/kvm/kvm.ko]
> >> Error 1
> >> make[2]: *** Deleting file
> >> '/tmp/makepkg/linux-cachyos-rc-autofdo/pkg/linux-cachyos-rc-autofdo/usr/lib/modules/6.12.0-rc5-5-cachyos-rc-autofdo/kernel/arch/x86/kvm/kvm.ko'
> >>     INSTALL
> >> /tmp/makepkg/linux-cachyos-rc-autofdo/pkg/linux-cachyos-rc-autofdo/usr/lib/modules/6.12.0-rc5-5-cachyos-rc-autofdo/kernel/crypto/cryptd.ko
> >> make[2]: *** Waiting for unfinished jobs....
> >> ```
> >>
> >>
> >> This can be fixed with removed "INSTALL_MOD_STRIP=1" to the passed
> >> parameters of module_install.
> >>
> >> This explicitly only happens, if a profile is passed - otherwise the
> >> packaging works without problems.
> >>
> >> Regards,
> >>
> >> Peter Jung
> >>
>

Re: [PATCH v7 1/7] Add AutoFDO support for Clang build

Posted by Rong Xu 2 weeks, 5 days ago

We debugged this issue and we found the failure seems to only happen
with strip (version 2.43) in binutil.

For a profile-use compilation, either with -fprofile-use (PGO or
iFDO), or -fprofile-sample-use (AutoFDO),
an ELF section of .llvm.call-graph-profile is created for the object.
For some reasons (like to save space?),
the relocations in this section are of type "rel', rather the more
common "rela" type.

In this case,
$ readelf -r kvm.ko |grep llvm.call-graph-profile
Relocation section '.rel.llvm.call-graph-profile' at offset 0xf62a00
contains 4 entries:

strip (v2.43.0) has difficulty handling the relocations in
.rel.llvm.call-graph-profile -- it silently failed with --strip-debug.
But strip (v.2.42) has no issue with kvm.ko. The strip in llvm (i.e.
llvm-strip) also passes with kvm.ko

I compared binutil/strip source code for version v2.43.0 and v2.42.
The different is around here:
In v2.42 of bfd/elfcode.h
   1618       if ((entsize == sizeof (Elf_External_Rela)
   1619            && ebd->elf_info_to_howto != NULL)
   1620           || ebd->elf_info_to_howto_rel == NULL)
   1621         res = ebd->elf_info_to_howto (abfd, relent, &rela);
   1622       else
   1623         res = ebd->elf_info_to_howto_rel (abfd, relent, &rela);

In v2.43.0 of bfd/elfcode.h
   1618       if (entsize == sizeof (Elf_External_Rela)
   1619           && ebd->elf_info_to_howto != NULL)
   1620         res = ebd->elf_info_to_howto (abfd, relent, &rela);
   1621       else if (ebd->elf_info_to_howto_rel != NULL)
   1622         res = ebd->elf_info_to_howto_rel (abfd, relent, &rela);

In the 2.43 strip, line 1618 is false and line 1621 is also false.
"res" is returned as false and the program exits with -1.

While in 2.42, line 1620 is true and we get "res" from line 1621 and
program functions correctly.

I'm not familiar with binutil code base and don't know the reason for
removing line 1620.
I can file a bug for binutil for people to further investigate this.

It seems to me that this issue should not be a blocker for our patch.

Regards,

-Rong





On Mon, Nov 4, 2024 at 12:24 PM Han Shen <shenhan@google.com> wrote:
>
> Hi Peter,
> Thanks for providing the detailed reproduce.
> Now I can see the error (after I synced to 6.12.0-rc6, I was using rc5).
> I'll look into that and report back.
>
> > I have tested your provided method, but the AutoFDO profile (lld does
> not get lto-sample-profile=$pathtoprofile passed)
>
> I see. You also turned on ThinLTO, which I didn't, so the profile was
> only used during compilation, not passed to lld.
>
> Thanks,
> Han
>
> On Mon, Nov 4, 2024 at 9:31 AM Peter Jung <ptr1337@cachyos.org> wrote:
> >
> > Hi Han,
> >
> > I have tested your provided method, but the AutoFDO profile (lld does
> > not get lto-sample-profile=$pathtoprofile passed)  nor Clang as compiler
> > gets used.
> > Please replace following PKGBUILD and config from linux-mainline with
> > the provided one in the gist. The patch is also included there.
> >
> > https://gist.github.com/ptr1337/c92728bb273f7dbc2817db75eedec9ed
> >
> > The main change I am doing here, is passing following to the build array
> > and replacing "make all":
> >
> > make LLVM=1 LLVM_IAS=1 CLANG_AUTOFDO_PROFILE=${srcdir}/perf.afdo all
> >
> > When compiling the kernel with makepkg, this results at the packaging to
> > following issue and can be reliable reproduced.
> >
> > Regards,
> >
> > Peter
> >
> >
> > On 04.11.24 05:50, Han Shen wrote:
> > > Hi Peter, thanks for reporting the issue. I am trying to reproduce it
> > > in the up-to-date archlinux environment. Below is what I have:
> > >    0. pacman -Syu
> > >    1. cloned archlinux build files from
> > > https://aur.archlinux.org/linux-mainline.git the newest mainline
> > > version is 6.12rc5-1.
> > >    2. changed the PKGBUILD file to include the patches series
> > >    3. changed the "config" to turn on clang autofdo
> > >    4. collected afdo profiles
> > >    5. MAKEFLAGS="-j48 V=1 LLVM=1 CLANG_AUTOFDO_PROFILE=$(pwd)/perf.afdo" \
> > >          makepkg -s --skipinteg --skippgp
> > >    6. install and reboot
> > > The above steps succeeded.
> > > You mentioned the error happens at "module_install", can you instruct
> > > me how to execute the "module_install" step?
> > >
> > > Thanks,
> > > Han
> > >
> > > On Sat, Nov 2, 2024 at 12:53 PM Peter Jung<ptr1337@cachyos.org> wrote:
> > >>
> > >>
> > >> On 02.11.24 20:46, Peter Jung wrote:
> > >>>
> > >>> On 02.11.24 18:51, Rong Xu wrote:
> > >>>> Add the build support for using Clang's AutoFDO. Building the kernel
> > >>>> with AutoFDO does not reduce the optimization level from the
> > >>>> compiler. AutoFDO uses hardware sampling to gather information about
> > >>>> the frequency of execution of different code paths within a binary.
> > >>>> This information is then used to guide the compiler's optimization
> > >>>> decisions, resulting in a more efficient binary. Experiments
> > >>>> showed that the kernel can improve up to 10% in latency.
> > >>>>
> > >>>> The support requires a Clang compiler after LLVM 17. This submission
> > >>>> is limited to x86 platforms that support PMU features like LBR on
> > >>>> Intel machines and AMD Zen3 BRS. Support for SPE on ARM 1,
> > >>>>    and BRBE on ARM 1 is part of planned future work.
> > >>>>
> > >>>> Here is an example workflow for AutoFDO kernel:
> > >>>>
> > >>>> 1) Build the kernel on the host machine with LLVM enabled, for example,
> > >>>>          $ make menuconfig LLVM=1
> > >>>>       Turn on AutoFDO build config:
> > >>>>         CONFIG_AUTOFDO_CLANG=y
> > >>>>       With a configuration that has LLVM enabled, use the following
> > >>>>       command:
> > >>>>          scripts/config -e AUTOFDO_CLANG
> > >>>>       After getting the config, build with
> > >>>>         $ make LLVM=1
> > >>>>
> > >>>> 2) Install the kernel on the test machine.
> > >>>>
> > >>>> 3) Run the load tests. The '-c' option in perf specifies the sample
> > >>>>      event period. We suggest     using a suitable prime number,
> > >>>>      like 500009, for this purpose.
> > >>>>      For Intel platforms:
> > >>>>         $ perf record -e BR_INST_RETIRED.NEAR_TAKEN:k -a -N -b -c
> > >>>> <count> \
> > >>>>           -o <perf_file> -- <loadtest>
> > >>>>      For AMD platforms:
> > >>>>         The supported system are: Zen3 with BRS, or Zen4 with amd_lbr_v2
> > >>>>        For Zen3:
> > >>>>         $ cat proc/cpuinfo | grep " brs"
> > >>>>         For Zen4:
> > >>>>         $ cat proc/cpuinfo | grep amd_lbr_v2
> > >>>>         $ perf record --pfm-events RETIRED_TAKEN_BRANCH_INSTRUCTIONS:k
> > >>>> -a \
> > >>>>           -N -b -c <count> -o <perf_file> -- <loadtest>
> > >>>>
> > >>>> 4) (Optional) Download the raw perf file to the host machine.
> > >>>>
> > >>>> 5) To generate an AutoFDO profile, two offline tools are available:
> > >>>>      create_llvm_prof and llvm_profgen. The create_llvm_prof tool is part
> > >>>>      of the AutoFDO project and can be found on GitHub
> > >>>>      (https://github.com/google/autofdo), version v0.30.1 or later. The
> > >>>>      llvm_profgen tool is included in the LLVM compiler itself. It's
> > >>>>      important to note that the version of llvm_profgen doesn't need to
> > >>>>      match the version of Clang. It needs to be the LLVM 19 release or
> > >>>>      later, or from the LLVM trunk.
> > >>>>         $ llvm-profgen --kernel --binary=<vmlinux> --
> > >>>> perfdata=<perf_file> \
> > >>>>           -o <profile_file>
> > >>>>      or
> > >>>>         $ create_llvm_prof --binary=<vmlinux> --profile=<perf_file> \
> > >>>>           --format=extbinary --out=<profile_file>
> > >>>>
> > >>>>      Note that multiple AutoFDO profile files can be merged into one via:
> > >>>>         $ llvm-profdata merge -o <profile_file>  <profile_1> ...
> > >>>> <profile_n>
> > >>>>
> > >>>> 6) Rebuild the kernel using the AutoFDO profile file with the same config
> > >>>>      as step 1, (Note CONFIG_AUTOFDO_CLANG needs to be enabled):
> > >>>>         $ make LLVM=1 CLANG_AUTOFDO_PROFILE=<profile_file>
> > >>>>
> > >>>> Co-developed-by: Han Shen<shenhan@google.com>
> > >>>> Signed-off-by: Han Shen<shenhan@google.com>
> > >>>> Signed-off-by: Rong Xu<xur@google.com>
> > >>>> Suggested-by: Sriraman Tallam<tmsriram@google.com>
> > >>>> Suggested-by: Krzysztof Pszeniczny<kpszeniczny@google.com>
> > >>>> Suggested-by: Nick Desaulniers<ndesaulniers@google.com>
> > >>>> Suggested-by: Stephane Eranian<eranian@google.com>
> > >>>> Tested-by: Yonghong Song<yonghong.song@linux.dev>
> > >>>> Tested-by: Yabin Cui<yabinc@google.com>
> > >>>> Tested-by: Nathan Chancellor<nathan@kernel.org>
> > >>>> Reviewed-by: Kees Cook<kees@kernel.org>
> > >>> Tested-by: Peter Jung<ptr1337@cachyos.org>
> > >>>
> > >> The compilations and testing with the "make pacman-pkg" function from
> > >> the kernel worked fine.
> > >>
> > >> One problem I do face:
> > >> When I apply a AutoFDO profile together with the PKGBUILD [1] from
> > >> archlinux im running into issues at "module_install" at the packaging.
> > >>
> > >> See following log:
> > >> ```
> > >> make[2]: *** [scripts/Makefile.modinst:125:
> > >> /tmp/makepkg/linux-cachyos-rc-autofdo/pkg/linux-cachyos-rc-autofdo/usr/lib/modules/6.12.0-rc5-5-cachyos-rc-autofdo/kernel/arch/x86/kvm/kvm.ko]
> > >> Error 1
> > >> make[2]: *** Deleting file
> > >> '/tmp/makepkg/linux-cachyos-rc-autofdo/pkg/linux-cachyos-rc-autofdo/usr/lib/modules/6.12.0-rc5-5-cachyos-rc-autofdo/kernel/arch/x86/kvm/kvm.ko'
> > >>     INSTALL
> > >> /tmp/makepkg/linux-cachyos-rc-autofdo/pkg/linux-cachyos-rc-autofdo/usr/lib/modules/6.12.0-rc5-5-cachyos-rc-autofdo/kernel/crypto/cryptd.ko
> > >> make[2]: *** Waiting for unfinished jobs....
> > >> ```
> > >>
> > >>
> > >> This can be fixed with removed "INSTALL_MOD_STRIP=1" to the passed
> > >> parameters of module_install.
> > >>
> > >> This explicitly only happens, if a profile is passed - otherwise the
> > >> packaging works without problems.
> > >>
> > >> Regards,
> > >>
> > >> Peter Jung
> > >>
> >

Re: [PATCH v7 1/7] Add AutoFDO support for Clang build

Posted by Peter Jung 2 weeks, 5 days ago

Hi Rong,

Glad that you were able to reproduce the issue!
Thanks for finding the root cause as well as the part of the code. This 
really helps.

I was able to do a successful packaging with binutils 2.42.
Lets forward this to the binutils tracker and hope this will be soon 
solved. :)

I have tested this also on the latest commit 
(e1e4078ac59740a79cd709d61872abe15aba0087) and the issue is also 
reproducible there.

Thanks for your time! I dont see this as blocker. :)
It gets time to get this series merged :P

Best regards,

Peter



On 05.11.24 08:25, Rong Xu wrote:
> We debugged this issue and we found the failure seems to only happen
> with strip (version 2.43) in binutil.
> 
> For a profile-use compilation, either with -fprofile-use (PGO or
> iFDO), or -fprofile-sample-use (AutoFDO),
> an ELF section of .llvm.call-graph-profile is created for the object.
> For some reasons (like to save space?),
> the relocations in this section are of type "rel', rather the more
> common "rela" type.
> 
> In this case,
> $ readelf -r kvm.ko |grep llvm.call-graph-profile
> Relocation section '.rel.llvm.call-graph-profile' at offset 0xf62a00
> contains 4 entries:
> 
> strip (v2.43.0) has difficulty handling the relocations in
> .rel.llvm.call-graph-profile -- it silently failed with --strip-debug.
> But strip (v.2.42) has no issue with kvm.ko. The strip in llvm (i.e.
> llvm-strip) also passes with kvm.ko
> 
> I compared binutil/strip source code for version v2.43.0 and v2.42.
> The different is around here:
> In v2.42 of bfd/elfcode.h
>     1618       if ((entsize == sizeof (Elf_External_Rela)
>     1619            && ebd->elf_info_to_howto != NULL)
>     1620           || ebd->elf_info_to_howto_rel == NULL)
>     1621         res = ebd->elf_info_to_howto (abfd, relent, &rela);
>     1622       else
>     1623         res = ebd->elf_info_to_howto_rel (abfd, relent, &rela);
> 
> In v2.43.0 of bfd/elfcode.h
>     1618       if (entsize == sizeof (Elf_External_Rela)
>     1619           && ebd->elf_info_to_howto != NULL)
>     1620         res = ebd->elf_info_to_howto (abfd, relent, &rela);
>     1621       else if (ebd->elf_info_to_howto_rel != NULL)
>     1622         res = ebd->elf_info_to_howto_rel (abfd, relent, &rela);
> 
> In the 2.43 strip, line 1618 is false and line 1621 is also false.
> "res" is returned as false and the program exits with -1.
> 
> While in 2.42, line 1620 is true and we get "res" from line 1621 and
> program functions correctly.
> 
> I'm not familiar with binutil code base and don't know the reason for
> removing line 1620.
> I can file a bug for binutil for people to further investigate this.
> 
> It seems to me that this issue should not be a blocker for our patch.
> 
> Regards,
> 
> -Rong
> 
> 
> 
> 
> 
> On Mon, Nov 4, 2024 at 12:24 PM Han Shen<shenhan@google.com> wrote:
>> Hi Peter,
>> Thanks for providing the detailed reproduce.
>> Now I can see the error (after I synced to 6.12.0-rc6, I was using rc5).
>> I'll look into that and report back.
>>
>>> I have tested your provided method, but the AutoFDO profile (lld does
>> not get lto-sample-profile=$pathtoprofile passed)
>>
>> I see. You also turned on ThinLTO, which I didn't, so the profile was
>> only used during compilation, not passed to lld.
>>
>> Thanks,
>> Han
>>
>> On Mon, Nov 4, 2024 at 9:31 AM Peter Jung<ptr1337@cachyos.org> wrote:
>>> Hi Han,
>>>
>>> I have tested your provided method, but the AutoFDO profile (lld does
>>> not get lto-sample-profile=$pathtoprofile passed)  nor Clang as compiler
>>> gets used.
>>> Please replace following PKGBUILD and config from linux-mainline with
>>> the provided one in the gist. The patch is also included there.
>>>
>>> https://gist.github.com/ptr1337/c92728bb273f7dbc2817db75eedec9ed
>>>
>>> The main change I am doing here, is passing following to the build array
>>> and replacing "make all":
>>>
>>> make LLVM=1 LLVM_IAS=1 CLANG_AUTOFDO_PROFILE=${srcdir}/perf.afdo all
>>>
>>> When compiling the kernel with makepkg, this results at the packaging to
>>> following issue and can be reliable reproduced.
>>>
>>> Regards,
>>>
>>> Peter
>>>
>>>
>>> On 04.11.24 05:50, Han Shen wrote:
>>>> Hi Peter, thanks for reporting the issue. I am trying to reproduce it
>>>> in the up-to-date archlinux environment. Below is what I have:
>>>>     0. pacman -Syu
>>>>     1. cloned archlinux build files from
>>>> https://aur.archlinux.org/linux-mainline.git the newest mainline
>>>> version is 6.12rc5-1.
>>>>     2. changed the PKGBUILD file to include the patches series
>>>>     3. changed the "config" to turn on clang autofdo
>>>>     4. collected afdo profiles
>>>>     5. MAKEFLAGS="-j48 V=1 LLVM=1 CLANG_AUTOFDO_PROFILE=$(pwd)/perf.afdo" \
>>>>           makepkg -s --skipinteg --skippgp
>>>>     6. install and reboot
>>>> The above steps succeeded.
>>>> You mentioned the error happens at "module_install", can you instruct
>>>> me how to execute the "module_install" step?
>>>>
>>>> Thanks,
>>>> Han
>>>>
>>>> On Sat, Nov 2, 2024 at 12:53 PM Peter Jung<ptr1337@cachyos.org> wrote:
>>>>>
>>>>> On 02.11.24 20:46, Peter Jung wrote:
>>>>>> On 02.11.24 18:51, Rong Xu wrote:
>>>>>>> Add the build support for using Clang's AutoFDO. Building the kernel
>>>>>>> with AutoFDO does not reduce the optimization level from the
>>>>>>> compiler. AutoFDO uses hardware sampling to gather information about
>>>>>>> the frequency of execution of different code paths within a binary.
>>>>>>> This information is then used to guide the compiler's optimization
>>>>>>> decisions, resulting in a more efficient binary. Experiments
>>>>>>> showed that the kernel can improve up to 10% in latency.
>>>>>>>
>>>>>>> The support requires a Clang compiler after LLVM 17. This submission
>>>>>>> is limited to x86 platforms that support PMU features like LBR on
>>>>>>> Intel machines and AMD Zen3 BRS. Support for SPE on ARM 1,
>>>>>>>     and BRBE on ARM 1 is part of planned future work.
>>>>>>>
>>>>>>> Here is an example workflow for AutoFDO kernel:
>>>>>>>
>>>>>>> 1) Build the kernel on the host machine with LLVM enabled, for example,
>>>>>>>           $ make menuconfig LLVM=1
>>>>>>>        Turn on AutoFDO build config:
>>>>>>>          CONFIG_AUTOFDO_CLANG=y
>>>>>>>        With a configuration that has LLVM enabled, use the following
>>>>>>>        command:
>>>>>>>           scripts/config -e AUTOFDO_CLANG
>>>>>>>        After getting the config, build with
>>>>>>>          $ make LLVM=1
>>>>>>>
>>>>>>> 2) Install the kernel on the test machine.
>>>>>>>
>>>>>>> 3) Run the load tests. The '-c' option in perf specifies the sample
>>>>>>>       event period. We suggest     using a suitable prime number,
>>>>>>>       like 500009, for this purpose.
>>>>>>>       For Intel platforms:
>>>>>>>          $ perf record -e BR_INST_RETIRED.NEAR_TAKEN:k -a -N -b -c
>>>>>>> <count> \
>>>>>>>            -o <perf_file> -- <loadtest>
>>>>>>>       For AMD platforms:
>>>>>>>          The supported system are: Zen3 with BRS, or Zen4 with amd_lbr_v2
>>>>>>>         For Zen3:
>>>>>>>          $ cat proc/cpuinfo | grep " brs"
>>>>>>>          For Zen4:
>>>>>>>          $ cat proc/cpuinfo | grep amd_lbr_v2
>>>>>>>          $ perf record --pfm-events RETIRED_TAKEN_BRANCH_INSTRUCTIONS:k
>>>>>>> -a \
>>>>>>>            -N -b -c <count> -o <perf_file> -- <loadtest>
>>>>>>>
>>>>>>> 4) (Optional) Download the raw perf file to the host machine.
>>>>>>>
>>>>>>> 5) To generate an AutoFDO profile, two offline tools are available:
>>>>>>>       create_llvm_prof and llvm_profgen. The create_llvm_prof tool is part
>>>>>>>       of the AutoFDO project and can be found on GitHub
>>>>>>>       (https://github.com/google/autofdo), version v0.30.1 or later. The
>>>>>>>       llvm_profgen tool is included in the LLVM compiler itself. It's
>>>>>>>       important to note that the version of llvm_profgen doesn't need to
>>>>>>>       match the version of Clang. It needs to be the LLVM 19 release or
>>>>>>>       later, or from the LLVM trunk.
>>>>>>>          $ llvm-profgen --kernel --binary=<vmlinux> --
>>>>>>> perfdata=<perf_file> \
>>>>>>>            -o <profile_file>
>>>>>>>       or
>>>>>>>          $ create_llvm_prof --binary=<vmlinux> --profile=<perf_file> \
>>>>>>>            --format=extbinary --out=<profile_file>
>>>>>>>
>>>>>>>       Note that multiple AutoFDO profile files can be merged into one via:
>>>>>>>          $ llvm-profdata merge -o <profile_file>  <profile_1> ...
>>>>>>> <profile_n>
>>>>>>>
>>>>>>> 6) Rebuild the kernel using the AutoFDO profile file with the same config
>>>>>>>       as step 1, (Note CONFIG_AUTOFDO_CLANG needs to be enabled):
>>>>>>>          $ make LLVM=1 CLANG_AUTOFDO_PROFILE=<profile_file>
>>>>>>>
>>>>>>> Co-developed-by: Han Shen<shenhan@google.com>
>>>>>>> Signed-off-by: Han Shen<shenhan@google.com>
>>>>>>> Signed-off-by: Rong Xu<xur@google.com>
>>>>>>> Suggested-by: Sriraman Tallam<tmsriram@google.com>
>>>>>>> Suggested-by: Krzysztof Pszeniczny<kpszeniczny@google.com>
>>>>>>> Suggested-by: Nick Desaulniers<ndesaulniers@google.com>
>>>>>>> Suggested-by: Stephane Eranian<eranian@google.com>
>>>>>>> Tested-by: Yonghong Song<yonghong.song@linux.dev>
>>>>>>> Tested-by: Yabin Cui<yabinc@google.com>
>>>>>>> Tested-by: Nathan Chancellor<nathan@kernel.org>
>>>>>>> Reviewed-by: Kees Cook<kees@kernel.org>
>>>>>> Tested-by: Peter Jung<ptr1337@cachyos.org>
>>>>>>
>>>>> The compilations and testing with the "make pacman-pkg" function from
>>>>> the kernel worked fine.
>>>>>
>>>>> One problem I do face:
>>>>> When I apply a AutoFDO profile together with the PKGBUILD [1] from
>>>>> archlinux im running into issues at "module_install" at the packaging.
>>>>>
>>>>> See following log:
>>>>> ```
>>>>> make[2]: *** [scripts/Makefile.modinst:125:
>>>>> /tmp/makepkg/linux-cachyos-rc-autofdo/pkg/linux-cachyos-rc-autofdo/usr/lib/modules/6.12.0-rc5-5-cachyos-rc-autofdo/kernel/arch/x86/kvm/kvm.ko]
>>>>> Error 1
>>>>> make[2]: *** Deleting file
>>>>> '/tmp/makepkg/linux-cachyos-rc-autofdo/pkg/linux-cachyos-rc-autofdo/usr/lib/modules/6.12.0-rc5-5-cachyos-rc-autofdo/kernel/arch/x86/kvm/kvm.ko'
>>>>>      INSTALL
>>>>> /tmp/makepkg/linux-cachyos-rc-autofdo/pkg/linux-cachyos-rc-autofdo/usr/lib/modules/6.12.0-rc5-5-cachyos-rc-autofdo/kernel/crypto/cryptd.ko
>>>>> make[2]: *** Waiting for unfinished jobs....
>>>>> ```
>>>>>
>>>>>
>>>>> This can be fixed with removed "INSTALL_MOD_STRIP=1" to the passed
>>>>> parameters of module_install.
>>>>>
>>>>> This explicitly only happens, if a profile is passed - otherwise the
>>>>> packaging works without problems.
>>>>>
>>>>> Regards,
>>>>>
>>>>> Peter Jung
>>>>>

Re: [PATCH v7 1/7] Add AutoFDO support for Clang build

Posted by Peter Jung 2 weeks, 5 days ago

You were right - reverting commit:
https://github.com/bminor/binutils-gdb/commit/b20ab53f81db7eefa0db00d14f06c04527ac324c 
from the 2.43 branch does fix the packaging.

I will forward this to an issue at their bugzilla.

On 05.11.24 15:33, Peter Jung wrote:
> Hi Rong,
> 
> Glad that you were able to reproduce the issue!
> Thanks for finding the root cause as well as the part of the code. This 
> really helps.
> 
> I was able to do a successful packaging with binutils 2.42.
> Lets forward this to the binutils tracker and hope this will be soon 
> solved. 🙂
> 
> I have tested this also on the latest commit 
> (e1e4078ac59740a79cd709d61872abe15aba0087) and the issue is also 
> reproducible there.
> 
> Thanks for your time! I dont see this as blocker. 🙂
> It gets time to get this series merged :P
> 
> Best regards,
> 
> Peter
> 
> 
> 
> On 05.11.24 08:25, Rong Xu wrote:
>> We debugged this issue and we found the failure seems to only happen
>> with strip (version 2.43) in binutil.
>>
>> For a profile-use compilation, either with -fprofile-use (PGO or
>> iFDO), or -fprofile-sample-use (AutoFDO),
>> an ELF section of .llvm.call-graph-profile is created for the object.
>> For some reasons (like to save space?),
>> the relocations in this section are of type "rel', rather the more
>> common "rela" type.
>>
>> In this case,
>> $ readelf -r kvm.ko |grep llvm.call-graph-profile
>> Relocation section '.rel.llvm.call-graph-profile' at offset 0xf62a00
>> contains 4 entries:
>>
>> strip (v2.43.0) has difficulty handling the relocations in
>> .rel.llvm.call-graph-profile -- it silently failed with --strip-debug.
>> But strip (v.2.42) has no issue with kvm.ko. The strip in llvm (i.e.
>> llvm-strip) also passes with kvm.ko
>>
>> I compared binutil/strip source code for version v2.43.0 and v2.42.
>> The different is around here:
>> In v2.42 of bfd/elfcode.h
>>     1618       if ((entsize == sizeof (Elf_External_Rela)
>>     1619            && ebd->elf_info_to_howto != NULL)
>>     1620           || ebd->elf_info_to_howto_rel == NULL)
>>     1621         res = ebd->elf_info_to_howto (abfd, relent, &rela);
>>     1622       else
>>     1623         res = ebd->elf_info_to_howto_rel (abfd, relent, &rela);
>>
>> In v2.43.0 of bfd/elfcode.h
>>     1618       if (entsize == sizeof (Elf_External_Rela)
>>     1619           && ebd->elf_info_to_howto != NULL)
>>     1620         res = ebd->elf_info_to_howto (abfd, relent, &rela);
>>     1621       else if (ebd->elf_info_to_howto_rel != NULL)
>>     1622         res = ebd->elf_info_to_howto_rel (abfd, relent, &rela);
>>
>> In the 2.43 strip, line 1618 is false and line 1621 is also false.
>> "res" is returned as false and the program exits with -1.
>>
>> While in 2.42, line 1620 is true and we get "res" from line 1621 and
>> program functions correctly.
>>
>> I'm not familiar with binutil code base and don't know the reason for
>> removing line 1620.
>> I can file a bug for binutil for people to further investigate this.
>>
>> It seems to me that this issue should not be a blocker for our patch.
>>
>> Regards,
>>
>> -Rong
>>
>>
>>
>>
>>
>> On Mon, Nov 4, 2024 at 12:24 PM Han Shen<shenhan@google.com> wrote:
>>> Hi Peter,
>>> Thanks for providing the detailed reproduce.
>>> Now I can see the error (after I synced to 6.12.0-rc6, I was using rc5).
>>> I'll look into that and report back.
>>>
>>>> I have tested your provided method, but the AutoFDO profile (lld does
>>> not get lto-sample-profile=$pathtoprofile passed)
>>>
>>> I see. You also turned on ThinLTO, which I didn't, so the profile was
>>> only used during compilation, not passed to lld.
>>>
>>> Thanks,
>>> Han
>>>
>>> On Mon, Nov 4, 2024 at 9:31 AM Peter Jung<ptr1337@cachyos.org> wrote:
>>>> Hi Han,
>>>>
>>>> I have tested your provided method, but the AutoFDO profile (lld does
>>>> not get lto-sample-profile=$pathtoprofile passed)  nor Clang as 
>>>> compiler
>>>> gets used.
>>>> Please replace following PKGBUILD and config from linux-mainline with
>>>> the provided one in the gist. The patch is also included there.
>>>>
>>>> https://gist.github.com/ptr1337/c92728bb273f7dbc2817db75eedec9ed
>>>>
>>>> The main change I am doing here, is passing following to the build 
>>>> array
>>>> and replacing "make all":
>>>>
>>>> make LLVM=1 LLVM_IAS=1 CLANG_AUTOFDO_PROFILE=${srcdir}/perf.afdo all
>>>>
>>>> When compiling the kernel with makepkg, this results at the 
>>>> packaging to
>>>> following issue and can be reliable reproduced.
>>>>
>>>> Regards,
>>>>
>>>> Peter
>>>>
>>>>
>>>> On 04.11.24 05:50, Han Shen wrote:
>>>>> Hi Peter, thanks for reporting the issue. I am trying to reproduce it
>>>>> in the up-to-date archlinux environment. Below is what I have:
>>>>>     0. pacman -Syu
>>>>>     1. cloned archlinux build files from
>>>>> https://aur.archlinux.org/linux-mainline.git the newest mainline
>>>>> version is 6.12rc5-1.
>>>>>     2. changed the PKGBUILD file to include the patches series
>>>>>     3. changed the "config" to turn on clang autofdo
>>>>>     4. collected afdo profiles
>>>>>     5. MAKEFLAGS="-j48 V=1 LLVM=1 CLANG_AUTOFDO_PROFILE=$(pwd)/ 
>>>>> perf.afdo" \
>>>>>           makepkg -s --skipinteg --skippgp
>>>>>     6. install and reboot
>>>>> The above steps succeeded.
>>>>> You mentioned the error happens at "module_install", can you instruct
>>>>> me how to execute the "module_install" step?
>>>>>
>>>>> Thanks,
>>>>> Han
>>>>>
>>>>> On Sat, Nov 2, 2024 at 12:53 PM Peter Jung<ptr1337@cachyos.org> wrote:
>>>>>>
>>>>>> On 02.11.24 20:46, Peter Jung wrote:
>>>>>>> On 02.11.24 18:51, Rong Xu wrote:
>>>>>>>> Add the build support for using Clang's AutoFDO. Building the 
>>>>>>>> kernel
>>>>>>>> with AutoFDO does not reduce the optimization level from the
>>>>>>>> compiler. AutoFDO uses hardware sampling to gather information 
>>>>>>>> about
>>>>>>>> the frequency of execution of different code paths within a binary.
>>>>>>>> This information is then used to guide the compiler's optimization
>>>>>>>> decisions, resulting in a more efficient binary. Experiments
>>>>>>>> showed that the kernel can improve up to 10% in latency.
>>>>>>>>
>>>>>>>> The support requires a Clang compiler after LLVM 17. This 
>>>>>>>> submission
>>>>>>>> is limited to x86 platforms that support PMU features like LBR on
>>>>>>>> Intel machines and AMD Zen3 BRS. Support for SPE on ARM 1,
>>>>>>>>     and BRBE on ARM 1 is part of planned future work.
>>>>>>>>
>>>>>>>> Here is an example workflow for AutoFDO kernel:
>>>>>>>>
>>>>>>>> 1) Build the kernel on the host machine with LLVM enabled, for 
>>>>>>>> example,
>>>>>>>>           $ make menuconfig LLVM=1
>>>>>>>>        Turn on AutoFDO build config:
>>>>>>>>          CONFIG_AUTOFDO_CLANG=y
>>>>>>>>        With a configuration that has LLVM enabled, use the 
>>>>>>>> following
>>>>>>>>        command:
>>>>>>>>           scripts/config -e AUTOFDO_CLANG
>>>>>>>>        After getting the config, build with
>>>>>>>>          $ make LLVM=1
>>>>>>>>
>>>>>>>> 2) Install the kernel on the test machine.
>>>>>>>>
>>>>>>>> 3) Run the load tests. The '-c' option in perf specifies the sample
>>>>>>>>       event period. We suggest     using a suitable prime number,
>>>>>>>>       like 500009, for this purpose.
>>>>>>>>       For Intel platforms:
>>>>>>>>          $ perf record -e BR_INST_RETIRED.NEAR_TAKEN:k -a -N -b -c
>>>>>>>> <count> \
>>>>>>>>            -o <perf_file> -- <loadtest>
>>>>>>>>       For AMD platforms:
>>>>>>>>          The supported system are: Zen3 with BRS, or Zen4 with 
>>>>>>>> amd_lbr_v2
>>>>>>>>         For Zen3:
>>>>>>>>          $ cat proc/cpuinfo | grep " brs"
>>>>>>>>          For Zen4:
>>>>>>>>          $ cat proc/cpuinfo | grep amd_lbr_v2
>>>>>>>>          $ perf record --pfm-events 
>>>>>>>> RETIRED_TAKEN_BRANCH_INSTRUCTIONS:k
>>>>>>>> -a \
>>>>>>>>            -N -b -c <count> -o <perf_file> -- <loadtest>
>>>>>>>>
>>>>>>>> 4) (Optional) Download the raw perf file to the host machine.
>>>>>>>>
>>>>>>>> 5) To generate an AutoFDO profile, two offline tools are available:
>>>>>>>>       create_llvm_prof and llvm_profgen. The create_llvm_prof 
>>>>>>>> tool is part
>>>>>>>>       of the AutoFDO project and can be found on GitHub
>>>>>>>>       (https://github.com/google/autofdo), version v0.30.1 or 
>>>>>>>> later. The
>>>>>>>>       llvm_profgen tool is included in the LLVM compiler itself. 
>>>>>>>> It's
>>>>>>>>       important to note that the version of llvm_profgen doesn't 
>>>>>>>> need to
>>>>>>>>       match the version of Clang. It needs to be the LLVM 19 
>>>>>>>> release or
>>>>>>>>       later, or from the LLVM trunk.
>>>>>>>>          $ llvm-profgen --kernel --binary=<vmlinux> --
>>>>>>>> perfdata=<perf_file> \
>>>>>>>>            -o <profile_file>
>>>>>>>>       or
>>>>>>>>          $ create_llvm_prof --binary=<vmlinux> -- 
>>>>>>>> profile=<perf_file> \
>>>>>>>>            --format=extbinary --out=<profile_file>
>>>>>>>>
>>>>>>>>       Note that multiple AutoFDO profile files can be merged 
>>>>>>>> into one via:
>>>>>>>>          $ llvm-profdata merge -o <profile_file>  <profile_1> ...
>>>>>>>> <profile_n>
>>>>>>>>
>>>>>>>> 6) Rebuild the kernel using the AutoFDO profile file with the 
>>>>>>>> same config
>>>>>>>>       as step 1, (Note CONFIG_AUTOFDO_CLANG needs to be enabled):
>>>>>>>>          $ make LLVM=1 CLANG_AUTOFDO_PROFILE=<profile_file>
>>>>>>>>
>>>>>>>> Co-developed-by: Han Shen<shenhan@google.com>
>>>>>>>> Signed-off-by: Han Shen<shenhan@google.com>
>>>>>>>> Signed-off-by: Rong Xu<xur@google.com>
>>>>>>>> Suggested-by: Sriraman Tallam<tmsriram@google.com>
>>>>>>>> Suggested-by: Krzysztof Pszeniczny<kpszeniczny@google.com>
>>>>>>>> Suggested-by: Nick Desaulniers<ndesaulniers@google.com>
>>>>>>>> Suggested-by: Stephane Eranian<eranian@google.com>
>>>>>>>> Tested-by: Yonghong Song<yonghong.song@linux.dev>
>>>>>>>> Tested-by: Yabin Cui<yabinc@google.com>
>>>>>>>> Tested-by: Nathan Chancellor<nathan@kernel.org>
>>>>>>>> Reviewed-by: Kees Cook<kees@kernel.org>
>>>>>>> Tested-by: Peter Jung<ptr1337@cachyos.org>
>>>>>>>
>>>>>> The compilations and testing with the "make pacman-pkg" function from
>>>>>> the kernel worked fine.
>>>>>>
>>>>>> One problem I do face:
>>>>>> When I apply a AutoFDO profile together with the PKGBUILD [1] from
>>>>>> archlinux im running into issues at "module_install" at the 
>>>>>> packaging.
>>>>>>
>>>>>> See following log:
>>>>>> ```
>>>>>> make[2]: *** [scripts/Makefile.modinst:125:
>>>>>> /tmp/makepkg/linux-cachyos-rc-autofdo/pkg/linux-cachyos-rc- 
>>>>>> autofdo/usr/lib/modules/6.12.0-rc5-5-cachyos-rc-autofdo/kernel/ 
>>>>>> arch/x86/kvm/kvm.ko]
>>>>>> Error 1
>>>>>> make[2]: *** Deleting file
>>>>>> '/tmp/makepkg/linux-cachyos-rc-autofdo/pkg/linux-cachyos-rc- 
>>>>>> autofdo/usr/lib/modules/6.12.0-rc5-5-cachyos-rc-autofdo/kernel/ 
>>>>>> arch/x86/kvm/kvm.ko'
>>>>>>      INSTALL
>>>>>> /tmp/makepkg/linux-cachyos-rc-autofdo/pkg/linux-cachyos-rc- 
>>>>>> autofdo/usr/lib/modules/6.12.0-rc5-5-cachyos-rc-autofdo/kernel/ 
>>>>>> crypto/cryptd.ko
>>>>>> make[2]: *** Waiting for unfinished jobs....
>>>>>> ```
>>>>>>
>>>>>>
>>>>>> This can be fixed with removed "INSTALL_MOD_STRIP=1" to the passed
>>>>>> parameters of module_install.
>>>>>>
>>>>>> This explicitly only happens, if a profile is passed - otherwise the
>>>>>> packaging works without problems.
>>>>>>
>>>>>> Regards,
>>>>>>
>>>>>> Peter Jung
>>>>>>
>

Re: [PATCH v7 1/7] Add AutoFDO support for Clang build

Posted by Peter Jung 2 weeks, 5 days ago

Here the bugreport, in case someone wants to track it:

https://sourceware.org/bugzilla/show_bug.cgi?id=32340

On 05.11.24 15:56, Peter Jung wrote:
> You were right - reverting commit:
> https://github.com/bminor/binutils-gdb/commit/ 
> b20ab53f81db7eefa0db00d14f06c04527ac324c from the 2.43 branch does fix 
> the packaging.
> 
> I will forward this to an issue at their bugzilla.
> 
> On 05.11.24 15:33, Peter Jung wrote:
>> Hi Rong,
>>
>> Glad that you were able to reproduce the issue!
>> Thanks for finding the root cause as well as the part of the code. 
>> This really helps.
>>
>> I was able to do a successful packaging with binutils 2.42.
>> Lets forward this to the binutils tracker and hope this will be soon 
>> solved. 🙂
>>
>> I have tested this also on the latest commit 
>> (e1e4078ac59740a79cd709d61872abe15aba0087) and the issue is also 
>> reproducible there.
>>
>> Thanks for your time! I dont see this as blocker. 🙂
>> It gets time to get this series merged :P
>>
>> Best regards,
>>
>> Peter
>>
>>
>>
>> On 05.11.24 08:25, Rong Xu wrote:
>>> We debugged this issue and we found the failure seems to only happen
>>> with strip (version 2.43) in binutil.
>>>
>>> For a profile-use compilation, either with -fprofile-use (PGO or
>>> iFDO), or -fprofile-sample-use (AutoFDO),
>>> an ELF section of .llvm.call-graph-profile is created for the object.
>>> For some reasons (like to save space?),
>>> the relocations in this section are of type "rel', rather the more
>>> common "rela" type.
>>>
>>> In this case,
>>> $ readelf -r kvm.ko |grep llvm.call-graph-profile
>>> Relocation section '.rel.llvm.call-graph-profile' at offset 0xf62a00
>>> contains 4 entries:
>>>
>>> strip (v2.43.0) has difficulty handling the relocations in
>>> .rel.llvm.call-graph-profile -- it silently failed with --strip-debug.
>>> But strip (v.2.42) has no issue with kvm.ko. The strip in llvm (i.e.
>>> llvm-strip) also passes with kvm.ko
>>>
>>> I compared binutil/strip source code for version v2.43.0 and v2.42.
>>> The different is around here:
>>> In v2.42 of bfd/elfcode.h
>>>     1618       if ((entsize == sizeof (Elf_External_Rela)
>>>     1619            && ebd->elf_info_to_howto != NULL)
>>>     1620           || ebd->elf_info_to_howto_rel == NULL)
>>>     1621         res = ebd->elf_info_to_howto (abfd, relent, &rela);
>>>     1622       else
>>>     1623         res = ebd->elf_info_to_howto_rel (abfd, relent, &rela);
>>>
>>> In v2.43.0 of bfd/elfcode.h
>>>     1618       if (entsize == sizeof (Elf_External_Rela)
>>>     1619           && ebd->elf_info_to_howto != NULL)
>>>     1620         res = ebd->elf_info_to_howto (abfd, relent, &rela);
>>>     1621       else if (ebd->elf_info_to_howto_rel != NULL)
>>>     1622         res = ebd->elf_info_to_howto_rel (abfd, relent, &rela);
>>>
>>> In the 2.43 strip, line 1618 is false and line 1621 is also false.
>>> "res" is returned as false and the program exits with -1.
>>>
>>> While in 2.42, line 1620 is true and we get "res" from line 1621 and
>>> program functions correctly.
>>>
>>> I'm not familiar with binutil code base and don't know the reason for
>>> removing line 1620.
>>> I can file a bug for binutil for people to further investigate this.
>>>
>>> It seems to me that this issue should not be a blocker for our patch.
>>>
>>> Regards,
>>>
>>> -Rong
>>>
>>>
>>>
>>>
>>>
>>> On Mon, Nov 4, 2024 at 12:24 PM Han Shen<shenhan@google.com> wrote:
>>>> Hi Peter,
>>>> Thanks for providing the detailed reproduce.
>>>> Now I can see the error (after I synced to 6.12.0-rc6, I was using 
>>>> rc5).
>>>> I'll look into that and report back.
>>>>
>>>>> I have tested your provided method, but the AutoFDO profile (lld does
>>>> not get lto-sample-profile=$pathtoprofile passed)
>>>>
>>>> I see. You also turned on ThinLTO, which I didn't, so the profile was
>>>> only used during compilation, not passed to lld.
>>>>
>>>> Thanks,
>>>> Han
>>>>
>>>> On Mon, Nov 4, 2024 at 9:31 AM Peter Jung<ptr1337@cachyos.org> wrote:
>>>>> Hi Han,
>>>>>
>>>>> I have tested your provided method, but the AutoFDO profile (lld does
>>>>> not get lto-sample-profile=$pathtoprofile passed)  nor Clang as 
>>>>> compiler
>>>>> gets used.
>>>>> Please replace following PKGBUILD and config from linux-mainline with
>>>>> the provided one in the gist. The patch is also included there.
>>>>>
>>>>> https://gist.github.com/ptr1337/c92728bb273f7dbc2817db75eedec9ed
>>>>>
>>>>> The main change I am doing here, is passing following to the build 
>>>>> array
>>>>> and replacing "make all":
>>>>>
>>>>> make LLVM=1 LLVM_IAS=1 CLANG_AUTOFDO_PROFILE=${srcdir}/perf.afdo all
>>>>>
>>>>> When compiling the kernel with makepkg, this results at the 
>>>>> packaging to
>>>>> following issue and can be reliable reproduced.
>>>>>
>>>>> Regards,
>>>>>
>>>>> Peter
>>>>>
>>>>>
>>>>> On 04.11.24 05:50, Han Shen wrote:
>>>>>> Hi Peter, thanks for reporting the issue. I am trying to reproduce it
>>>>>> in the up-to-date archlinux environment. Below is what I have:
>>>>>>     0. pacman -Syu
>>>>>>     1. cloned archlinux build files from
>>>>>> https://aur.archlinux.org/linux-mainline.git the newest mainline
>>>>>> version is 6.12rc5-1.
>>>>>>     2. changed the PKGBUILD file to include the patches series
>>>>>>     3. changed the "config" to turn on clang autofdo
>>>>>>     4. collected afdo profiles
>>>>>>     5. MAKEFLAGS="-j48 V=1 LLVM=1 CLANG_AUTOFDO_PROFILE=$(pwd)/ 
>>>>>> perf.afdo" \
>>>>>>           makepkg -s --skipinteg --skippgp
>>>>>>     6. install and reboot
>>>>>> The above steps succeeded.
>>>>>> You mentioned the error happens at "module_install", can you instruct
>>>>>> me how to execute the "module_install" step?
>>>>>>
>>>>>> Thanks,
>>>>>> Han
>>>>>>
>>>>>> On Sat, Nov 2, 2024 at 12:53 PM Peter Jung<ptr1337@cachyos.org> 
>>>>>> wrote:
>>>>>>>
>>>>>>> On 02.11.24 20:46, Peter Jung wrote:
>>>>>>>> On 02.11.24 18:51, Rong Xu wrote:
>>>>>>>>> Add the build support for using Clang's AutoFDO. Building the 
>>>>>>>>> kernel
>>>>>>>>> with AutoFDO does not reduce the optimization level from the
>>>>>>>>> compiler. AutoFDO uses hardware sampling to gather information 
>>>>>>>>> about
>>>>>>>>> the frequency of execution of different code paths within a 
>>>>>>>>> binary.
>>>>>>>>> This information is then used to guide the compiler's optimization
>>>>>>>>> decisions, resulting in a more efficient binary. Experiments
>>>>>>>>> showed that the kernel can improve up to 10% in latency.
>>>>>>>>>
>>>>>>>>> The support requires a Clang compiler after LLVM 17. This 
>>>>>>>>> submission
>>>>>>>>> is limited to x86 platforms that support PMU features like LBR on
>>>>>>>>> Intel machines and AMD Zen3 BRS. Support for SPE on ARM 1,
>>>>>>>>>     and BRBE on ARM 1 is part of planned future work.
>>>>>>>>>
>>>>>>>>> Here is an example workflow for AutoFDO kernel:
>>>>>>>>>
>>>>>>>>> 1) Build the kernel on the host machine with LLVM enabled, for 
>>>>>>>>> example,
>>>>>>>>>           $ make menuconfig LLVM=1
>>>>>>>>>        Turn on AutoFDO build config:
>>>>>>>>>          CONFIG_AUTOFDO_CLANG=y
>>>>>>>>>        With a configuration that has LLVM enabled, use the 
>>>>>>>>> following
>>>>>>>>>        command:
>>>>>>>>>           scripts/config -e AUTOFDO_CLANG
>>>>>>>>>        After getting the config, build with
>>>>>>>>>          $ make LLVM=1
>>>>>>>>>
>>>>>>>>> 2) Install the kernel on the test machine.
>>>>>>>>>
>>>>>>>>> 3) Run the load tests. The '-c' option in perf specifies the 
>>>>>>>>> sample
>>>>>>>>>       event period. We suggest     using a suitable prime number,
>>>>>>>>>       like 500009, for this purpose.
>>>>>>>>>       For Intel platforms:
>>>>>>>>>          $ perf record -e BR_INST_RETIRED.NEAR_TAKEN:k -a -N -b -c
>>>>>>>>> <count> \
>>>>>>>>>            -o <perf_file> -- <loadtest>
>>>>>>>>>       For AMD platforms:
>>>>>>>>>          The supported system are: Zen3 with BRS, or Zen4 with 
>>>>>>>>> amd_lbr_v2
>>>>>>>>>         For Zen3:
>>>>>>>>>          $ cat proc/cpuinfo | grep " brs"
>>>>>>>>>          For Zen4:
>>>>>>>>>          $ cat proc/cpuinfo | grep amd_lbr_v2
>>>>>>>>>          $ perf record --pfm-events 
>>>>>>>>> RETIRED_TAKEN_BRANCH_INSTRUCTIONS:k
>>>>>>>>> -a \
>>>>>>>>>            -N -b -c <count> -o <perf_file> -- <loadtest>
>>>>>>>>>
>>>>>>>>> 4) (Optional) Download the raw perf file to the host machine.
>>>>>>>>>
>>>>>>>>> 5) To generate an AutoFDO profile, two offline tools are 
>>>>>>>>> available:
>>>>>>>>>       create_llvm_prof and llvm_profgen. The create_llvm_prof 
>>>>>>>>> tool is part
>>>>>>>>>       of the AutoFDO project and can be found on GitHub
>>>>>>>>>       (https://github.com/google/autofdo), version v0.30.1 or 
>>>>>>>>> later. The
>>>>>>>>>       llvm_profgen tool is included in the LLVM compiler 
>>>>>>>>> itself. It's
>>>>>>>>>       important to note that the version of llvm_profgen 
>>>>>>>>> doesn't need to
>>>>>>>>>       match the version of Clang. It needs to be the LLVM 19 
>>>>>>>>> release or
>>>>>>>>>       later, or from the LLVM trunk.
>>>>>>>>>          $ llvm-profgen --kernel --binary=<vmlinux> --
>>>>>>>>> perfdata=<perf_file> \
>>>>>>>>>            -o <profile_file>
>>>>>>>>>       or
>>>>>>>>>          $ create_llvm_prof --binary=<vmlinux> -- 
>>>>>>>>> profile=<perf_file> \
>>>>>>>>>            --format=extbinary --out=<profile_file>
>>>>>>>>>
>>>>>>>>>       Note that multiple AutoFDO profile files can be merged 
>>>>>>>>> into one via:
>>>>>>>>>          $ llvm-profdata merge -o <profile_file>  <profile_1> ...
>>>>>>>>> <profile_n>
>>>>>>>>>
>>>>>>>>> 6) Rebuild the kernel using the AutoFDO profile file with the 
>>>>>>>>> same config
>>>>>>>>>       as step 1, (Note CONFIG_AUTOFDO_CLANG needs to be enabled):
>>>>>>>>>          $ make LLVM=1 CLANG_AUTOFDO_PROFILE=<profile_file>
>>>>>>>>>
>>>>>>>>> Co-developed-by: Han Shen<shenhan@google.com>
>>>>>>>>> Signed-off-by: Han Shen<shenhan@google.com>
>>>>>>>>> Signed-off-by: Rong Xu<xur@google.com>
>>>>>>>>> Suggested-by: Sriraman Tallam<tmsriram@google.com>
>>>>>>>>> Suggested-by: Krzysztof Pszeniczny<kpszeniczny@google.com>
>>>>>>>>> Suggested-by: Nick Desaulniers<ndesaulniers@google.com>
>>>>>>>>> Suggested-by: Stephane Eranian<eranian@google.com>
>>>>>>>>> Tested-by: Yonghong Song<yonghong.song@linux.dev>
>>>>>>>>> Tested-by: Yabin Cui<yabinc@google.com>
>>>>>>>>> Tested-by: Nathan Chancellor<nathan@kernel.org>
>>>>>>>>> Reviewed-by: Kees Cook<kees@kernel.org>
>>>>>>>> Tested-by: Peter Jung<ptr1337@cachyos.org>
>>>>>>>>
>>>>>>> The compilations and testing with the "make pacman-pkg" function 
>>>>>>> from
>>>>>>> the kernel worked fine.
>>>>>>>
>>>>>>> One problem I do face:
>>>>>>> When I apply a AutoFDO profile together with the PKGBUILD [1] from
>>>>>>> archlinux im running into issues at "module_install" at the 
>>>>>>> packaging.
>>>>>>>
>>>>>>> See following log:
>>>>>>> ```
>>>>>>> make[2]: *** [scripts/Makefile.modinst:125:
>>>>>>> /tmp/makepkg/linux-cachyos-rc-autofdo/pkg/linux-cachyos-rc- 
>>>>>>> autofdo/usr/lib/modules/6.12.0-rc5-5-cachyos-rc-autofdo/kernel/ 
>>>>>>> arch/x86/kvm/kvm.ko]
>>>>>>> Error 1
>>>>>>> make[2]: *** Deleting file
>>>>>>> '/tmp/makepkg/linux-cachyos-rc-autofdo/pkg/linux-cachyos-rc- 
>>>>>>> autofdo/usr/lib/modules/6.12.0-rc5-5-cachyos-rc-autofdo/kernel/ 
>>>>>>> arch/x86/kvm/kvm.ko'
>>>>>>>      INSTALL
>>>>>>> /tmp/makepkg/linux-cachyos-rc-autofdo/pkg/linux-cachyos-rc- 
>>>>>>> autofdo/usr/lib/modules/6.12.0-rc5-5-cachyos-rc-autofdo/kernel/ 
>>>>>>> crypto/cryptd.ko
>>>>>>> make[2]: *** Waiting for unfinished jobs....
>>>>>>> ```
>>>>>>>
>>>>>>>
>>>>>>> This can be fixed with removed "INSTALL_MOD_STRIP=1" to the passed
>>>>>>> parameters of module_install.
>>>>>>>
>>>>>>> This explicitly only happens, if a profile is passed - otherwise the
>>>>>>> packaging works without problems.
>>>>>>>
>>>>>>> Regards,
>>>>>>>
>>>>>>> Peter Jung
>>>>>>>
>>
>

Re: [PATCH v7 1/7] Add AutoFDO support for Clang build

Posted by Rong Xu 2 weeks, 5 days ago

Hi Peter, thanks for verifying and filing the bug report!

-Rong

On Tue, Nov 5, 2024 at 9:19 AM Peter Jung <ptr1337@cachyos.org> wrote:
>
> Here the bugreport, in case someone wants to track it:
>
> https://sourceware.org/bugzilla/show_bug.cgi?id=32340
>
> On 05.11.24 15:56, Peter Jung wrote:
> > You were right - reverting commit:
> > https://github.com/bminor/binutils-gdb/commit/
> > b20ab53f81db7eefa0db00d14f06c04527ac324c from the 2.43 branch does fix
> > the packaging.
> >
> > I will forward this to an issue at their bugzilla.
> >
> > On 05.11.24 15:33, Peter Jung wrote:
> >> Hi Rong,
> >>
> >> Glad that you were able to reproduce the issue!
> >> Thanks for finding the root cause as well as the part of the code.
> >> This really helps.
> >>
> >> I was able to do a successful packaging with binutils 2.42.
> >> Lets forward this to the binutils tracker and hope this will be soon
> >> solved. 🙂
> >>
> >> I have tested this also on the latest commit
> >> (e1e4078ac59740a79cd709d61872abe15aba0087) and the issue is also
> >> reproducible there.
> >>
> >> Thanks for your time! I dont see this as blocker. 🙂
> >> It gets time to get this series merged :P
> >>
> >> Best regards,
> >>
> >> Peter
> >>
> >>
> >>
> >> On 05.11.24 08:25, Rong Xu wrote:
> >>> We debugged this issue and we found the failure seems to only happen
> >>> with strip (version 2.43) in binutil.
> >>>
> >>> For a profile-use compilation, either with -fprofile-use (PGO or
> >>> iFDO), or -fprofile-sample-use (AutoFDO),
> >>> an ELF section of .llvm.call-graph-profile is created for the object.
> >>> For some reasons (like to save space?),
> >>> the relocations in this section are of type "rel', rather the more
> >>> common "rela" type.
> >>>
> >>> In this case,
> >>> $ readelf -r kvm.ko |grep llvm.call-graph-profile
> >>> Relocation section '.rel.llvm.call-graph-profile' at offset 0xf62a00
> >>> contains 4 entries:
> >>>
> >>> strip (v2.43.0) has difficulty handling the relocations in
> >>> .rel.llvm.call-graph-profile -- it silently failed with --strip-debug.
> >>> But strip (v.2.42) has no issue with kvm.ko. The strip in llvm (i.e.
> >>> llvm-strip) also passes with kvm.ko
> >>>
> >>> I compared binutil/strip source code for version v2.43.0 and v2.42.
> >>> The different is around here:
> >>> In v2.42 of bfd/elfcode.h
> >>>     1618       if ((entsize == sizeof (Elf_External_Rela)
> >>>     1619            && ebd->elf_info_to_howto != NULL)
> >>>     1620           || ebd->elf_info_to_howto_rel == NULL)
> >>>     1621         res = ebd->elf_info_to_howto (abfd, relent, &rela);
> >>>     1622       else
> >>>     1623         res = ebd->elf_info_to_howto_rel (abfd, relent, &rela);
> >>>
> >>> In v2.43.0 of bfd/elfcode.h
> >>>     1618       if (entsize == sizeof (Elf_External_Rela)
> >>>     1619           && ebd->elf_info_to_howto != NULL)
> >>>     1620         res = ebd->elf_info_to_howto (abfd, relent, &rela);
> >>>     1621       else if (ebd->elf_info_to_howto_rel != NULL)
> >>>     1622         res = ebd->elf_info_to_howto_rel (abfd, relent, &rela);
> >>>
> >>> In the 2.43 strip, line 1618 is false and line 1621 is also false.
> >>> "res" is returned as false and the program exits with -1.
> >>>
> >>> While in 2.42, line 1620 is true and we get "res" from line 1621 and
> >>> program functions correctly.
> >>>
> >>> I'm not familiar with binutil code base and don't know the reason for
> >>> removing line 1620.
> >>> I can file a bug for binutil for people to further investigate this.
> >>>
> >>> It seems to me that this issue should not be a blocker for our patch.
> >>>
> >>> Regards,
> >>>
> >>> -Rong
> >>>
> >>>
> >>>
> >>>
> >>>
> >>> On Mon, Nov 4, 2024 at 12:24 PM Han Shen<shenhan@google.com> wrote:
> >>>> Hi Peter,
> >>>> Thanks for providing the detailed reproduce.
> >>>> Now I can see the error (after I synced to 6.12.0-rc6, I was using
> >>>> rc5).
> >>>> I'll look into that and report back.
> >>>>
> >>>>> I have tested your provided method, but the AutoFDO profile (lld does
> >>>> not get lto-sample-profile=$pathtoprofile passed)
> >>>>
> >>>> I see. You also turned on ThinLTO, which I didn't, so the profile was
> >>>> only used during compilation, not passed to lld.
> >>>>
> >>>> Thanks,
> >>>> Han
> >>>>
> >>>> On Mon, Nov 4, 2024 at 9:31 AM Peter Jung<ptr1337@cachyos.org> wrote:
> >>>>> Hi Han,
> >>>>>
> >>>>> I have tested your provided method, but the AutoFDO profile (lld does
> >>>>> not get lto-sample-profile=$pathtoprofile passed)  nor Clang as
> >>>>> compiler
> >>>>> gets used.
> >>>>> Please replace following PKGBUILD and config from linux-mainline with
> >>>>> the provided one in the gist. The patch is also included there.
> >>>>>
> >>>>> https://gist.github.com/ptr1337/c92728bb273f7dbc2817db75eedec9ed
> >>>>>
> >>>>> The main change I am doing here, is passing following to the build
> >>>>> array
> >>>>> and replacing "make all":
> >>>>>
> >>>>> make LLVM=1 LLVM_IAS=1 CLANG_AUTOFDO_PROFILE=${srcdir}/perf.afdo all
> >>>>>
> >>>>> When compiling the kernel with makepkg, this results at the
> >>>>> packaging to
> >>>>> following issue and can be reliable reproduced.
> >>>>>
> >>>>> Regards,
> >>>>>
> >>>>> Peter
> >>>>>
> >>>>>
> >>>>> On 04.11.24 05:50, Han Shen wrote:
> >>>>>> Hi Peter, thanks for reporting the issue. I am trying to reproduce it
> >>>>>> in the up-to-date archlinux environment. Below is what I have:
> >>>>>>     0. pacman -Syu
> >>>>>>     1. cloned archlinux build files from
> >>>>>> https://aur.archlinux.org/linux-mainline.git the newest mainline
> >>>>>> version is 6.12rc5-1.
> >>>>>>     2. changed the PKGBUILD file to include the patches series
> >>>>>>     3. changed the "config" to turn on clang autofdo
> >>>>>>     4. collected afdo profiles
> >>>>>>     5. MAKEFLAGS="-j48 V=1 LLVM=1 CLANG_AUTOFDO_PROFILE=$(pwd)/
> >>>>>> perf.afdo" \
> >>>>>>           makepkg -s --skipinteg --skippgp
> >>>>>>     6. install and reboot
> >>>>>> The above steps succeeded.
> >>>>>> You mentioned the error happens at "module_install", can you instruct
> >>>>>> me how to execute the "module_install" step?
> >>>>>>
> >>>>>> Thanks,
> >>>>>> Han
> >>>>>>
> >>>>>> On Sat, Nov 2, 2024 at 12:53 PM Peter Jung<ptr1337@cachyos.org>
> >>>>>> wrote:
> >>>>>>>
> >>>>>>> On 02.11.24 20:46, Peter Jung wrote:
> >>>>>>>> On 02.11.24 18:51, Rong Xu wrote:
> >>>>>>>>> Add the build support for using Clang's AutoFDO. Building the
> >>>>>>>>> kernel
> >>>>>>>>> with AutoFDO does not reduce the optimization level from the
> >>>>>>>>> compiler. AutoFDO uses hardware sampling to gather information
> >>>>>>>>> about
> >>>>>>>>> the frequency of execution of different code paths within a
> >>>>>>>>> binary.
> >>>>>>>>> This information is then used to guide the compiler's optimization
> >>>>>>>>> decisions, resulting in a more efficient binary. Experiments
> >>>>>>>>> showed that the kernel can improve up to 10% in latency.
> >>>>>>>>>
> >>>>>>>>> The support requires a Clang compiler after LLVM 17. This
> >>>>>>>>> submission
> >>>>>>>>> is limited to x86 platforms that support PMU features like LBR on
> >>>>>>>>> Intel machines and AMD Zen3 BRS. Support for SPE on ARM 1,
> >>>>>>>>>     and BRBE on ARM 1 is part of planned future work.
> >>>>>>>>>
> >>>>>>>>> Here is an example workflow for AutoFDO kernel:
> >>>>>>>>>
> >>>>>>>>> 1) Build the kernel on the host machine with LLVM enabled, for
> >>>>>>>>> example,
> >>>>>>>>>           $ make menuconfig LLVM=1
> >>>>>>>>>        Turn on AutoFDO build config:
> >>>>>>>>>          CONFIG_AUTOFDO_CLANG=y
> >>>>>>>>>        With a configuration that has LLVM enabled, use the
> >>>>>>>>> following
> >>>>>>>>>        command:
> >>>>>>>>>           scripts/config -e AUTOFDO_CLANG
> >>>>>>>>>        After getting the config, build with
> >>>>>>>>>          $ make LLVM=1
> >>>>>>>>>
> >>>>>>>>> 2) Install the kernel on the test machine.
> >>>>>>>>>
> >>>>>>>>> 3) Run the load tests. The '-c' option in perf specifies the
> >>>>>>>>> sample
> >>>>>>>>>       event period. We suggest     using a suitable prime number,
> >>>>>>>>>       like 500009, for this purpose.
> >>>>>>>>>       For Intel platforms:
> >>>>>>>>>          $ perf record -e BR_INST_RETIRED.NEAR_TAKEN:k -a -N -b -c
> >>>>>>>>> <count> \
> >>>>>>>>>            -o <perf_file> -- <loadtest>
> >>>>>>>>>       For AMD platforms:
> >>>>>>>>>          The supported system are: Zen3 with BRS, or Zen4 with
> >>>>>>>>> amd_lbr_v2
> >>>>>>>>>         For Zen3:
> >>>>>>>>>          $ cat proc/cpuinfo | grep " brs"
> >>>>>>>>>          For Zen4:
> >>>>>>>>>          $ cat proc/cpuinfo | grep amd_lbr_v2
> >>>>>>>>>          $ perf record --pfm-events
> >>>>>>>>> RETIRED_TAKEN_BRANCH_INSTRUCTIONS:k
> >>>>>>>>> -a \
> >>>>>>>>>            -N -b -c <count> -o <perf_file> -- <loadtest>
> >>>>>>>>>
> >>>>>>>>> 4) (Optional) Download the raw perf file to the host machine.
> >>>>>>>>>
> >>>>>>>>> 5) To generate an AutoFDO profile, two offline tools are
> >>>>>>>>> available:
> >>>>>>>>>       create_llvm_prof and llvm_profgen. The create_llvm_prof
> >>>>>>>>> tool is part
> >>>>>>>>>       of the AutoFDO project and can be found on GitHub
> >>>>>>>>>       (https://github.com/google/autofdo), version v0.30.1 or
> >>>>>>>>> later. The
> >>>>>>>>>       llvm_profgen tool is included in the LLVM compiler
> >>>>>>>>> itself. It's
> >>>>>>>>>       important to note that the version of llvm_profgen
> >>>>>>>>> doesn't need to
> >>>>>>>>>       match the version of Clang. It needs to be the LLVM 19
> >>>>>>>>> release or
> >>>>>>>>>       later, or from the LLVM trunk.
> >>>>>>>>>          $ llvm-profgen --kernel --binary=<vmlinux> --
> >>>>>>>>> perfdata=<perf_file> \
> >>>>>>>>>            -o <profile_file>
> >>>>>>>>>       or
> >>>>>>>>>          $ create_llvm_prof --binary=<vmlinux> --
> >>>>>>>>> profile=<perf_file> \
> >>>>>>>>>            --format=extbinary --out=<profile_file>
> >>>>>>>>>
> >>>>>>>>>       Note that multiple AutoFDO profile files can be merged
> >>>>>>>>> into one via:
> >>>>>>>>>          $ llvm-profdata merge -o <profile_file>  <profile_1> ...
> >>>>>>>>> <profile_n>
> >>>>>>>>>
> >>>>>>>>> 6) Rebuild the kernel using the AutoFDO profile file with the
> >>>>>>>>> same config
> >>>>>>>>>       as step 1, (Note CONFIG_AUTOFDO_CLANG needs to be enabled):
> >>>>>>>>>          $ make LLVM=1 CLANG_AUTOFDO_PROFILE=<profile_file>
> >>>>>>>>>
> >>>>>>>>> Co-developed-by: Han Shen<shenhan@google.com>
> >>>>>>>>> Signed-off-by: Han Shen<shenhan@google.com>
> >>>>>>>>> Signed-off-by: Rong Xu<xur@google.com>
> >>>>>>>>> Suggested-by: Sriraman Tallam<tmsriram@google.com>
> >>>>>>>>> Suggested-by: Krzysztof Pszeniczny<kpszeniczny@google.com>
> >>>>>>>>> Suggested-by: Nick Desaulniers<ndesaulniers@google.com>
> >>>>>>>>> Suggested-by: Stephane Eranian<eranian@google.com>
> >>>>>>>>> Tested-by: Yonghong Song<yonghong.song@linux.dev>
> >>>>>>>>> Tested-by: Yabin Cui<yabinc@google.com>
> >>>>>>>>> Tested-by: Nathan Chancellor<nathan@kernel.org>
> >>>>>>>>> Reviewed-by: Kees Cook<kees@kernel.org>
> >>>>>>>> Tested-by: Peter Jung<ptr1337@cachyos.org>
> >>>>>>>>
> >>>>>>> The compilations and testing with the "make pacman-pkg" function
> >>>>>>> from
> >>>>>>> the kernel worked fine.
> >>>>>>>
> >>>>>>> One problem I do face:
> >>>>>>> When I apply a AutoFDO profile together with the PKGBUILD [1] from
> >>>>>>> archlinux im running into issues at "module_install" at the
> >>>>>>> packaging.
> >>>>>>>
> >>>>>>> See following log:
> >>>>>>> ```
> >>>>>>> make[2]: *** [scripts/Makefile.modinst:125:
> >>>>>>> /tmp/makepkg/linux-cachyos-rc-autofdo/pkg/linux-cachyos-rc-
> >>>>>>> autofdo/usr/lib/modules/6.12.0-rc5-5-cachyos-rc-autofdo/kernel/
> >>>>>>> arch/x86/kvm/kvm.ko]
> >>>>>>> Error 1
> >>>>>>> make[2]: *** Deleting file
> >>>>>>> '/tmp/makepkg/linux-cachyos-rc-autofdo/pkg/linux-cachyos-rc-
> >>>>>>> autofdo/usr/lib/modules/6.12.0-rc5-5-cachyos-rc-autofdo/kernel/
> >>>>>>> arch/x86/kvm/kvm.ko'
> >>>>>>>      INSTALL
> >>>>>>> /tmp/makepkg/linux-cachyos-rc-autofdo/pkg/linux-cachyos-rc-
> >>>>>>> autofdo/usr/lib/modules/6.12.0-rc5-5-cachyos-rc-autofdo/kernel/
> >>>>>>> crypto/cryptd.ko
> >>>>>>> make[2]: *** Waiting for unfinished jobs....
> >>>>>>> ```
> >>>>>>>
> >>>>>>>
> >>>>>>> This can be fixed with removed "INSTALL_MOD_STRIP=1" to the passed
> >>>>>>> parameters of module_install.
> >>>>>>>
> >>>>>>> This explicitly only happens, if a profile is passed - otherwise the
> >>>>>>> packaging works without problems.
> >>>>>>>
> >>>>>>> Regards,
> >>>>>>>
> >>>>>>> Peter Jung
> >>>>>>>
> >>
> >
>

Re: [PATCH v7 1/7] Add AutoFDO support for Clang build

Posted by Peter Jung 2 weeks, 6 days ago

Hi Han,

Thanks for the test. I will look into my current setup again and will 
let you know.

Please do not see this as blocker for now. :)

Regards,

Peter

On 04.11.24 05:50, Han Shen wrote:
> Hi Peter, thanks for reporting the issue. I am trying to reproduce it
> in the up-to-date archlinux environment. Below is what I have:
>    0. pacman -Syu
>    1. cloned archlinux build files from
> https://aur.archlinux.org/linux-mainline.git the newest mainline
> version is 6.12rc5-1.
>    2. changed the PKGBUILD file to include the patches series
>    3. changed the "config" to turn on clang autofdo
>    4. collected afdo profiles
>    5. MAKEFLAGS="-j48 V=1 LLVM=1 CLANG_AUTOFDO_PROFILE=$(pwd)/perf.afdo" \
>          makepkg -s --skipinteg --skippgp
>    6. install and reboot
> The above steps succeeded.
> You mentioned the error happens at "module_install", can you instruct
> me how to execute the "module_install" step?
> 
> Thanks,
> Han
> 
> On Sat, Nov 2, 2024 at 12:53 PM Peter Jung<ptr1337@cachyos.org> wrote:
>>
>>
>> On 02.11.24 20:46, Peter Jung wrote:
>>>
>>> On 02.11.24 18:51, Rong Xu wrote:
>>>> Add the build support for using Clang's AutoFDO. Building the kernel
>>>> with AutoFDO does not reduce the optimization level from the
>>>> compiler. AutoFDO uses hardware sampling to gather information about
>>>> the frequency of execution of different code paths within a binary.
>>>> This information is then used to guide the compiler's optimization
>>>> decisions, resulting in a more efficient binary. Experiments
>>>> showed that the kernel can improve up to 10% in latency.
>>>>
>>>> The support requires a Clang compiler after LLVM 17. This submission
>>>> is limited to x86 platforms that support PMU features like LBR on
>>>> Intel machines and AMD Zen3 BRS. Support for SPE on ARM 1,
>>>>    and BRBE on ARM 1 is part of planned future work.
>>>>
>>>> Here is an example workflow for AutoFDO kernel:
>>>>
>>>> 1) Build the kernel on the host machine with LLVM enabled, for example,
>>>>          $ make menuconfig LLVM=1
>>>>       Turn on AutoFDO build config:
>>>>         CONFIG_AUTOFDO_CLANG=y
>>>>       With a configuration that has LLVM enabled, use the following
>>>>       command:
>>>>          scripts/config -e AUTOFDO_CLANG
>>>>       After getting the config, build with
>>>>         $ make LLVM=1
>>>>
>>>> 2) Install the kernel on the test machine.
>>>>
>>>> 3) Run the load tests. The '-c' option in perf specifies the sample
>>>>      event period. We suggest     using a suitable prime number,
>>>>      like 500009, for this purpose.
>>>>      For Intel platforms:
>>>>         $ perf record -e BR_INST_RETIRED.NEAR_TAKEN:k -a -N -b -c
>>>> <count> \
>>>>           -o <perf_file> -- <loadtest>
>>>>      For AMD platforms:
>>>>         The supported system are: Zen3 with BRS, or Zen4 with amd_lbr_v2
>>>>        For Zen3:
>>>>         $ cat proc/cpuinfo | grep " brs"
>>>>         For Zen4:
>>>>         $ cat proc/cpuinfo | grep amd_lbr_v2
>>>>         $ perf record --pfm-events RETIRED_TAKEN_BRANCH_INSTRUCTIONS:k
>>>> -a \
>>>>           -N -b -c <count> -o <perf_file> -- <loadtest>
>>>>
>>>> 4) (Optional) Download the raw perf file to the host machine.
>>>>
>>>> 5) To generate an AutoFDO profile, two offline tools are available:
>>>>      create_llvm_prof and llvm_profgen. The create_llvm_prof tool is part
>>>>      of the AutoFDO project and can be found on GitHub
>>>>      (https://github.com/google/autofdo), version v0.30.1 or later. The
>>>>      llvm_profgen tool is included in the LLVM compiler itself. It's
>>>>      important to note that the version of llvm_profgen doesn't need to
>>>>      match the version of Clang. It needs to be the LLVM 19 release or
>>>>      later, or from the LLVM trunk.
>>>>         $ llvm-profgen --kernel --binary=<vmlinux> --
>>>> perfdata=<perf_file> \
>>>>           -o <profile_file>
>>>>      or
>>>>         $ create_llvm_prof --binary=<vmlinux> --profile=<perf_file> \
>>>>           --format=extbinary --out=<profile_file>
>>>>
>>>>      Note that multiple AutoFDO profile files can be merged into one via:
>>>>         $ llvm-profdata merge -o <profile_file>  <profile_1> ...
>>>> <profile_n>
>>>>
>>>> 6) Rebuild the kernel using the AutoFDO profile file with the same config
>>>>      as step 1, (Note CONFIG_AUTOFDO_CLANG needs to be enabled):
>>>>         $ make LLVM=1 CLANG_AUTOFDO_PROFILE=<profile_file>
>>>>
>>>> Co-developed-by: Han Shen<shenhan@google.com>
>>>> Signed-off-by: Han Shen<shenhan@google.com>
>>>> Signed-off-by: Rong Xu<xur@google.com>
>>>> Suggested-by: Sriraman Tallam<tmsriram@google.com>
>>>> Suggested-by: Krzysztof Pszeniczny<kpszeniczny@google.com>
>>>> Suggested-by: Nick Desaulniers<ndesaulniers@google.com>
>>>> Suggested-by: Stephane Eranian<eranian@google.com>
>>>> Tested-by: Yonghong Song<yonghong.song@linux.dev>
>>>> Tested-by: Yabin Cui<yabinc@google.com>
>>>> Tested-by: Nathan Chancellor<nathan@kernel.org>
>>>> Reviewed-by: Kees Cook<kees@kernel.org>
>>> Tested-by: Peter Jung<ptr1337@cachyos.org>
>>>
>> The compilations and testing with the "make pacman-pkg" function from
>> the kernel worked fine.
>>
>> One problem I do face:
>> When I apply a AutoFDO profile together with the PKGBUILD [1] from
>> archlinux im running into issues at "module_install" at the packaging.
>>
>> See following log:
>> ```
>> make[2]: *** [scripts/Makefile.modinst:125:
>> /tmp/makepkg/linux-cachyos-rc-autofdo/pkg/linux-cachyos-rc-autofdo/usr/lib/modules/6.12.0-rc5-5-cachyos-rc-autofdo/kernel/arch/x86/kvm/kvm.ko]
>> Error 1
>> make[2]: *** Deleting file
>> '/tmp/makepkg/linux-cachyos-rc-autofdo/pkg/linux-cachyos-rc-autofdo/usr/lib/modules/6.12.0-rc5-5-cachyos-rc-autofdo/kernel/arch/x86/kvm/kvm.ko'
>>     INSTALL
>> /tmp/makepkg/linux-cachyos-rc-autofdo/pkg/linux-cachyos-rc-autofdo/usr/lib/modules/6.12.0-rc5-5-cachyos-rc-autofdo/kernel/crypto/cryptd.ko
>> make[2]: *** Waiting for unfinished jobs....
>> ```
>>
>>
>> This can be fixed with removed "INSTALL_MOD_STRIP=1" to the passed
>> parameters of module_install.
>>
>> This explicitly only happens, if a profile is passed - otherwise the
>> packaging works without problems.
>>
>> Regards,
>>
>> Peter Jung
>>