Add the build support for using Clang's Propeller optimizer. Like
AutoFDO, Propeller 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.
The support requires a Clang compiler LLVM 19 or later, and the
create_llvm_prof tool
(https://github.com/google/autofdo/releases/tag/v0.30.1). This
submission is limited to x86 platforms that support PMU features
like LBR on Intel machines and AMD Zen3 BRS.
For Arm, we plan to send patches for SPE-based Propeller when
AutoFDO for Arm is ready.
Here is an example workflow for building an AutoFDO+Propeller
optimized kernel:
1) Build the kernel on the HOST machine, with AutoFDO and Propeller
build config
CONFIG_AUTOFDO_CLANG=y
CONFIG_PROPELLER_CLANG=y
then
$ make LLVM=1 CLANG_AUTOFDO_PROFILE=<autofdo_profile>
“<autofdo_profile>” is the profile collected when doing a non-Propeller
AutoFDO build. This step builds a kernel that has the same optimization
level as AutoFDO, plus a metadata section that records basic block
information. This kernel image runs as fast as an AutoFDO optimized
kernel.
2) Install the kernel on test/production machines.
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
# To see if Zen3 support LBR:
$ cat proc/cpuinfo | grep " brs"
# To see if Zen4 support LBR:
$ cat proc/cpuinfo | grep amd_lbr_v2
# If the result is yes, then collect the profile using:
$ 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) Generate Propeller profile:
$ create_llvm_prof --binary=<vmlinux> --profile=<perf_file> \
--format=propeller --propeller_output_module_name \
--out=<propeller_profile_prefix>_cc_profile.txt \
--propeller_symorder=<propeller_profile_prefix>_ld_profile.txt
“create_llvm_prof” is the profile conversion tool, and a prebuilt
binary for linux can be found on
https://github.com/google/autofdo/releases/tag/v0.30.1 (can also build
from source).
"<propeller_profile_prefix>" can be something like
"/home/user/dir/any_string".
This command generates a pair of Propeller profiles:
"<propeller_profile_prefix>_cc_profile.txt" and
"<propeller_profile_prefix>_ld_profile.txt".
6) Rebuild the kernel using the AutoFDO and Propeller profile files.
CONFIG_AUTOFDO_CLANG=y
CONFIG_PROPELLER_CLANG=y
and
$ make LLVM=1 CLANG_AUTOFDO_PROFILE=<autofdo_profile> \
CLANG_PROPELLER_PROFILE_PREFIX=<propeller_profile_prefix>
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>
---
Documentation/dev-tools/index.rst | 1 +
Documentation/dev-tools/propeller.rst | 161 ++++++++++++++++++++++++++
MAINTAINERS | 7 ++
Makefile | 1 +
arch/Kconfig | 22 ++++
arch/x86/Kconfig | 1 +
arch/x86/kernel/vmlinux.lds.S | 4 +
include/asm-generic/vmlinux.lds.h | 10 +-
scripts/Makefile.lib | 10 ++
scripts/Makefile.propeller | 28 +++++
tools/objtool/check.c | 1 +
11 files changed, 241 insertions(+), 5 deletions(-)
create mode 100644 Documentation/dev-tools/propeller.rst
create mode 100644 scripts/Makefile.propeller
diff --git a/Documentation/dev-tools/index.rst b/Documentation/dev-tools/index.rst
index 6945644f7008..3c0ac08b2709 100644
--- a/Documentation/dev-tools/index.rst
+++ b/Documentation/dev-tools/index.rst
@@ -35,6 +35,7 @@ Documentation/dev-tools/testing-overview.rst
checkuapi
gpio-sloppy-logic-analyzer
autofdo
+ propeller
.. only:: subproject and html
diff --git a/Documentation/dev-tools/propeller.rst b/Documentation/dev-tools/propeller.rst
new file mode 100644
index 000000000000..a217354e0f95
--- /dev/null
+++ b/Documentation/dev-tools/propeller.rst
@@ -0,0 +1,161 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=====================================
+Using Propeller with the Linux kernel
+=====================================
+
+This enables Propeller build support for the kernel when using Clang
+compiler. Propeller is a profile-guided optimization (PGO) method used
+to optimize binary executables. Like AutoFDO, it utilizes hardware
+sampling to gather information about the frequency of execution of
+different code paths within a binary. Unlike AutoFDO, this information
+is then used right before linking phase to optimize (among others)
+block layout within and across functions.
+
+A few important notes about adopting Propeller optimization:
+
+#. Although it can be used as a standalone optimization step, it is
+ strongly recommended to apply Propeller on top of AutoFDO,
+ AutoFDO+ThinLTO or Instrument FDO. The rest of this document
+ assumes this paradigm.
+
+#. Propeller uses another round of profiling on top of
+ AutoFDO/AutoFDO+ThinLTO/iFDO. The whole build process involves
+ "build-afdo - train-afdo - build-propeller - train-propeller -
+ build-optimized".
+
+#. Propeller requires LLVM 19 release or later for Clang/Clang++
+ and the linker(ld.lld).
+
+#. In addition to LLVM toolchain, Propeller requires a profiling
+ conversion tool: https://github.com/google/autofdo with a release
+ after v0.30.1: https://github.com/google/autofdo/releases/tag/v0.30.1.
+
+The Propeller optimization process involves the following steps:
+
+#. Initial building: Build the AutoFDO or AutoFDO+ThinLTO binary as
+ you would normally do, but with a set of compile-time / link-time
+ flags, so that a special metadata section is created within the
+ kernel binary. The special section is only intend to be used by the
+ profiling tool, it is not part of the runtime image, nor does it
+ change kernel run time text sections.
+
+#. 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. Propeller is most effective on
+ platforms supporting advanced PMU features like LBR on Intel
+ machines. This step is the same as profiling the kernel for AutoFDO
+ (the exact perf parameters can be different).
+
+#. Propeller profile generation: Perf output file is converted to a
+ pair of Propeller profiles via an offline tool.
+
+#. Optimized build: Build the AutoFDO or AutoFDO+ThinLTO optimized
+ binary as you would normally do, but with a compile-time /
+ link-time flag to pick up the Propeller compile time and link time
+ profiles. This build step uses 3 profiles - the AutoFDO profile,
+ the Propeller compile-time profile and the Propeller link-time
+ profile.
+
+#. Deployment: The optimized kernel binary is deployed and used
+ in production environments, providing improved performance
+ and reduced latency.
+
+Preparation
+===========
+
+Configure the kernel with::
+
+ CONFIG_AUTOFDO_CLANG=y
+ CONFIG_PROPELLER_CLANG=y
+
+Customization
+=============
+
+You can enable or disable Propeller build for individual file and
+directories by adding a line similar to the following to the
+respective kernel Makefile:
+
+- For enabling a single file (e.g. foo.o)::
+
+ PROPELLER_PROFILE_foo.o := y
+
+- For enabling all files in one directory::
+
+ PROPELLER_PROFILE := y
+
+- For disabling one file::
+
+ PROPELLER_PROFILE_foo.o := n
+
+- For disabling all files in one directory::
+
+ PROPELLER__PROFILE := n
+
+
+Workflow
+========
+
+Here is an example workflow for building an AutoFDO+Propeller kernel:
+
+1) Assuming an AutoFDO profile is already collected following
+ instructions in the AutoFDO document, build the kernel on the HOST
+ machine, with AutoFDO and Propeller build configs ::
+
+ CONFIG_AUTOFDO_CLANG=y
+ CONFIG_PROPELLER_CLANG=y
+
+ and ::
+
+ $ make LLVM=1 CLANG_AUTOFDO_PROFILE=<autofdo-profile-name>
+
+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::
+
+ $ perf record --pfm-event RETIRED_TAKEN_BRANCH_INSTRUCTIONS:k -a -N -b -c <count> -o <perf_file> -- <loadtest>
+
+ Note you can repeat the above steps to collect multiple <perf_file>s.
+
+4) (Optional) Download the raw perf file(s) to the HOST machine.
+
+5) Use the create_llvm_prof tool (https://github.com/google/autofdo) to
+ generate Propeller profile. ::
+
+ $ create_llvm_prof --binary=<vmlinux> --profile=<perf_file>
+ --format=propeller --propeller_output_module_name
+ --out=<propeller_profile_prefix>_cc_profile.txt
+ --propeller_symorder=<propeller_profile_prefix>_ld_profile.txt
+
+ "<propeller_profile_prefix>" can be something like "/home/user/dir/any_string".
+
+ This command generates a pair of Propeller profiles:
+ "<propeller_profile_prefix>_cc_profile.txt" and
+ "<propeller_profile_prefix>_ld_profile.txt".
+
+ If there are more than 1 perf_file collected in the previous step,
+ you can create a temp list file "<perf_file_list>" with each line
+ containing one perf file name and run::
+
+ $ create_llvm_prof --binary=<vmlinux> --profile=@<perf_file_list>
+ --format=propeller --propeller_output_module_name
+ --out=<propeller_profile_prefix>_cc_profile.txt
+ --propeller_symorder=<propeller_profile_prefix>_ld_profile.txt
+
+6) Rebuild the kernel using the AutoFDO and Propeller
+ profiles. ::
+
+ CONFIG_AUTOFDO_CLANG=y
+ CONFIG_PROPELLER_CLANG=y
+
+ and ::
+
+ $ make LLVM=1 CLANG_AUTOFDO_PROFILE=<profile_file> CLANG_PROPELLER_PROFILE_PREFIX=<propeller_profile_prefix>
diff --git a/MAINTAINERS b/MAINTAINERS
index 1b8db863031f..f4cc6dd6c4d8 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -18560,6 +18560,13 @@ S: Maintained
F: include/linux/psi*
F: kernel/sched/psi.c
+PROPELLER BUILD
+M: Rong Xu <xur@google.com>
+M: Han Shen <shenhan@google.com>
+S: Supported
+F: Documentation/dev-tools/propeller.rst
+F: scripts/Makefile.propeller
+
PRINTK
M: Petr Mladek <pmladek@suse.com>
R: Steven Rostedt <rostedt@goodmis.org>
diff --git a/Makefile b/Makefile
index bbb6ec68f5dc..2d2f688c21c6 100644
--- a/Makefile
+++ b/Makefile
@@ -1019,6 +1019,7 @@ 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-$(CONFIG_PROPELLER_CLANG) += scripts/Makefile.propeller
include-$(CONFIG_GCC_PLUGINS) += scripts/Makefile.gcc-plugins
include $(addprefix $(srctree)/, $(include-y))
diff --git a/arch/Kconfig b/arch/Kconfig
index 5e9604960cbb..fdeb5f173a10 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -831,6 +831,28 @@ config AUTOFDO_CLANG
If unsure, say N.
+config ARCH_SUPPORTS_PROPELLER_CLANG
+ bool
+
+config PROPELLER_CLANG
+ bool "Enable Clang's Propeller build"
+ depends on ARCH_SUPPORTS_PROPELLER_CLANG
+ depends on AUTOFDO_CLANG
+ depends on CC_IS_CLANG && CLANG_VERSION >= 190000
+ help
+ This option enables Clang’s Propeller build which
+ is on top of AutoFDO build. When the Propeller profiles
+ is specified in variable CLANG_PROPELLER_PROFILE_PREFIX
+ during the build process, Clang uses the profiles to
+ optimize the kernel.
+
+ If no profile is specified, Proepller options are
+ still passed to Clang to facilitate the collection
+ of perf data for creating the Propeller profiles 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 503a0268155a..da47164bfddc 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -127,6 +127,7 @@ config X86
select ARCH_SUPPORTS_LTO_CLANG_THIN
select ARCH_SUPPORTS_RT
select ARCH_SUPPORTS_AUTOFDO_CLANG
+ select ARCH_SUPPORTS_PROPELLER_CLANG if X86_64
select ARCH_USE_BUILTIN_BSWAP
select ARCH_USE_CMPXCHG_LOCKREF if X86_CMPXCHG64
select ARCH_USE_MEMTEST
diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index 6726be89b7a6..7ecc21c569be 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -442,6 +442,10 @@ SECTIONS
STABS_DEBUG
DWARF_DEBUG
+#ifdef CONFIG_PROPELLER_CLANG
+ .llvm_bb_addr_map : { *(.llvm_bb_addr_map) }
+#endif
+
ELF_DETAILS
DISCARDS
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 20e46c0917db..5986dd4cfb14 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -95,14 +95,14 @@
* With LTO_CLANG, the linker also splits sections by default, so we need
* these macros to combine the sections during the final link.
*
- * With LTO_CLANG, the linker also splits sections by default, so we need
- * these macros to combine the sections during the final link.
+ * CONFIG_AUTOFD_CLANG and CONFIG_PROPELLER_CLANG will also split text sections
+ * and cluster them in the linking time.
*
* RODATA_MAIN is not used because existing code already defines .rodata.x
* sections to be brought in with rodata.
*/
#if defined(CONFIG_LD_DEAD_CODE_DATA_ELIMINATION) || defined(CONFIG_LTO_CLANG) || \
-defined(CONFIG_AUTOFDO_CLANG)
+defined(CONFIG_AUTOFDO_CLANG) || defined(CONFIG_PROPELLER_CLANG)
#define TEXT_MAIN .text .text.[0-9a-zA-Z_]*
#else
#define TEXT_MAIN .text
@@ -556,7 +556,7 @@ defined(CONFIG_AUTOFDO_CLANG)
__cpuidle_text_end = .; \
__noinstr_text_end = .;
-#ifdef CONFIG_AUTOFDO_CLANG
+#if defined(CONFIG_AUTOFDO_CLANG) || defined(CONFIG_PROPELLER_CLANG)
#define TEXT_HOT \
__hot_text_start = .; \
*(.text.hot .text.hot.*) \
@@ -584,7 +584,7 @@ defined(CONFIG_AUTOFDO_CLANG)
* first when in these builds.
*/
#if defined(CONFIG_LD_DEAD_CODE_DATA_ELIMINATION) || defined(CONFIG_LTO_CLANG) || \
-defined(CONFIG_AUTOFDO_CLANG)
+defined(CONFIG_AUTOFDO_CLANG) || defined(CONFIG_PROPELLER_CLANG)
#define TEXT_TEXT \
ALIGN_FUNCTION(); \
*(.text.asan.* .text.tsan.*) \
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index e85d6ac31bd9..60354c476956 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -201,6 +201,16 @@ _c_flags += $(if $(patsubst n%,, \
$(CFLAGS_AUTOFDO_CLANG))
endif
+#
+# Enable Clang's Propeller build flags for a file or directory depending on
+# variables AUTOFDO_PROPELLER_obj.o and PROPELLER_PROFILE.
+#
+ifeq ($(CONFIG_PROPELLER_CLANG),y)
+_c_flags += $(if $(patsubst n%,, \
+ $(AUTOFDO_PROFILE_$(target-stem).o)$(AUTOFDO_PROFILE)$(PROPELLER_PROFILE))$(is-kernel-object), \
+ $(CFLAGS_PROPELLER_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/scripts/Makefile.propeller b/scripts/Makefile.propeller
new file mode 100644
index 000000000000..344190717e47
--- /dev/null
+++ b/scripts/Makefile.propeller
@@ -0,0 +1,28 @@
+# SPDX-License-Identifier: GPL-2.0
+
+# Enable available and selected Clang Propeller features.
+ifdef CLANG_PROPELLER_PROFILE_PREFIX
+ CFLAGS_PROPELLER_CLANG := -fbasic-block-sections=list=$(CLANG_PROPELLER_PROFILE_PREFIX)_cc_profile.txt -ffunction-sections
+ KBUILD_LDFLAGS += --symbol-ordering-file=$(CLANG_PROPELLER_PROFILE_PREFIX)_ld_profile.txt --no-warn-symbol-ordering
+else
+ CFLAGS_PROPELLER_CLANG := -fbasic-block-sections=labels
+endif
+
+# Propeller requires debug information to embed module names in the profiles.
+# If CONFIG_DEBUG_INFO is not enabled, set -gmlt option. Skip this for AutoFDO,
+# as the option should already be set.
+ifndef CONFIG_DEBUG_INFO
+ ifndef CONFIG_AUTOFDO_CLANG
+ CFLAGS_PROPELLER_CLANG += -gmlt
+ endif
+endif
+
+ifdef CONFIG_LTO_CLANG_THIN
+ ifdef CLANG_PROPELLER_PROFILE_PREFIX
+ KBUILD_LDFLAGS += --lto-basic-block-sections=$(CLANG_PROPELLER_PROFILE_PREFIX)_cc_profile.txt
+ else
+ KBUILD_LDFLAGS += --lto-basic-block-sections=labels
+ endif
+endif
+
+export CFLAGS_PROPELLER_CLANG
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 4c5229991e1e..05a0fb4a3d1a 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -4558,6 +4558,7 @@ static int validate_ibt(struct objtool_file *file)
!strcmp(sec->name, "__mcount_loc") ||
!strcmp(sec->name, ".kcfi_traps") ||
!strcmp(sec->name, ".llvm.call-graph-profile") ||
+ !strcmp(sec->name, ".llvm_bb_addr_map") ||
strstr(sec->name, "__patchable_function_entries"))
continue;
--
2.47.0.rc1.288.g06298d1525-googPlease remove the period at the end of the commit subject.
On Tue, Oct 15, 2024 at 6:34 AM Rong Xu <xur@google.com> wrote:
>
> Add the build support for using Clang's Propeller optimizer. Like
> AutoFDO, Propeller 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.
>
> The support requires a Clang compiler LLVM 19 or later, and the
> create_llvm_prof tool
> (https://github.com/google/autofdo/releases/tag/v0.30.1). This
> submission is limited to x86 platforms that support PMU features
"This submission" -> "This commit"
> like LBR on Intel machines and AMD Zen3 BRS.
>
> For Arm, we plan to send patches for SPE-based Propeller when
> AutoFDO for Arm is ready.
"we plan to send ..." is not a good description once it is committed.
This sentence should be moved to the cover letter, or reworked.
>
> Here is an example workflow for building an AutoFDO+Propeller
> optimized kernel:
>
> 1) Build the kernel on the HOST machine, with AutoFDO and Propeller
Why is the "HOST" capitalized?
> build config
> CONFIG_AUTOFDO_CLANG=y
> CONFIG_PROPELLER_CLANG=y
> then
> $ make LLVM=1 CLANG_AUTOFDO_PROFILE=<autofdo_profile>
>
> “<autofdo_profile>” is the profile collected when doing a non-Propeller
> AutoFDO build. This step builds a kernel that has the same optimization
> level as AutoFDO, plus a metadata section that records basic block
> information. This kernel image runs as fast as an AutoFDO optimized
> kernel.
>
> 2) Install the kernel on test/production machines.
>
> 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
> # To see if Zen3 support LBR:
> $ cat proc/cpuinfo | grep " brs"
> # To see if Zen4 support LBR:
> $ cat proc/cpuinfo | grep amd_lbr_v2
> # If the result is yes, then collect the profile using:
> $ 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.
Same question as above.
>
> 5) Generate Propeller profile:
> $ create_llvm_prof --binary=<vmlinux> --profile=<perf_file> \
> --format=propeller --propeller_output_module_name \
> --out=<propeller_profile_prefix>_cc_profile.txt \
> --propeller_symorder=<propeller_profile_prefix>_ld_profile.txt
>
> “create_llvm_prof” is the profile conversion tool, and a prebuilt
> binary for linux can be found on
> https://github.com/google/autofdo/releases/tag/v0.30.1 (can also build
> from source).
>
> "<propeller_profile_prefix>" can be something like
> "/home/user/dir/any_string".
>
> This command generates a pair of Propeller profiles:
> "<propeller_profile_prefix>_cc_profile.txt" and
> "<propeller_profile_prefix>_ld_profile.txt".
>
> 6) Rebuild the kernel using the AutoFDO and Propeller profile files.
> CONFIG_AUTOFDO_CLANG=y
> CONFIG_PROPELLER_CLANG=y
> and
> $ make LLVM=1 CLANG_AUTOFDO_PROFILE=<autofdo_profile> \
> CLANG_PROPELLER_PROFILE_PREFIX=<propeller_profile_prefix>
>
> 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>
>
> .. only:: subproject and html
> diff --git a/Documentation/dev-tools/propeller.rst b/Documentation/dev-tools/propeller.rst
> new file mode 100644
> index 000000000000..a217354e0f95
> --- /dev/null
> +++ b/Documentation/dev-tools/propeller.rst
> @@ -0,0 +1,161 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +
> +=====================================
> +Using Propeller with the Linux kernel
> +=====================================
> +
> +This enables Propeller build support for the kernel when using Clang
> +compiler. Propeller is a profile-guided optimization (PGO) method used
> +to optimize binary executables. Like AutoFDO, it utilizes hardware
> +sampling to gather information about the frequency of execution of
> +different code paths within a binary. Unlike AutoFDO, this information
> +is then used right before linking phase to optimize (among others)
> +block layout within and across functions.
> +
> +A few important notes about adopting Propeller optimization:
> +
> +#. Although it can be used as a standalone optimization step, it is
> + strongly recommended to apply Propeller on top of AutoFDO,
> + AutoFDO+ThinLTO or Instrument FDO. The rest of this document
> + assumes this paradigm.
This is a hard requirement instead of a recommendation
because PROPERLLER_CLANG has "depends on AUTOFDO_CLANG".
> +
> +#. Propeller uses another round of profiling on top of
> + AutoFDO/AutoFDO+ThinLTO/iFDO. The whole build process involves
> + "build-afdo - train-afdo - build-propeller - train-propeller -
> + build-optimized".
> +
> +#. Propeller requires LLVM 19 release or later for Clang/Clang++
> + and the linker(ld.lld).
> +
> +#. In addition to LLVM toolchain, Propeller requires a profiling
> + conversion tool: https://github.com/google/autofdo with a release
> + after v0.30.1: https://github.com/google/autofdo/releases/tag/v0.30.1.
> +
> +The Propeller optimization process involves the following steps:
> +
> +#. Initial building: Build the AutoFDO or AutoFDO+ThinLTO binary as
> + you would normally do, but with a set of compile-time / link-time
> + flags, so that a special metadata section is created within the
> + kernel binary. The special section is only intend to be used by the
> + profiling tool, it is not part of the runtime image, nor does it
> + change kernel run time text sections.
> +
> +#. 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. Propeller is most effective on
> + platforms supporting advanced PMU features like LBR on Intel
> + machines. This step is the same as profiling the kernel for AutoFDO
> + (the exact perf parameters can be different).
> +
> +#. Propeller profile generation: Perf output file is converted to a
> + pair of Propeller profiles via an offline tool.
> +
> +#. Optimized build: Build the AutoFDO or AutoFDO+ThinLTO optimized
> + binary as you would normally do, but with a compile-time /
> + link-time flag to pick up the Propeller compile time and link time
> + profiles. This build step uses 3 profiles - the AutoFDO profile,
> + the Propeller compile-time profile and the Propeller link-time
> + profile.
> +
> +#. Deployment: The optimized kernel binary is deployed and used
> + in production environments, providing improved performance
> + and reduced latency.
> +
> +Preparation
> +===========
> +
> +Configure the kernel with::
> +
> + CONFIG_AUTOFDO_CLANG=y
This is automatically met due to "depends on AUTOFDO_CLANG".
> + CONFIG_PROPELLER_CLANG=y
> +
> +Customization
> +=============
> +
> +You can enable or disable Propeller build for individual file and
> +directories by adding a line similar to the following to the
> +respective kernel Makefile:
The same comment as in 1/6.
> +- For enabling a single file (e.g. foo.o)::
> +
> + PROPELLER_PROFILE_foo.o := y
> +
> +- For enabling all files in one directory::
> +
> + PROPELLER_PROFILE := y
> +
> +- For disabling one file::
> +
> + PROPELLER_PROFILE_foo.o := n
> +
> +- For disabling all files in one directory::
> +
> + PROPELLER__PROFILE := n
> +
> +
> +Workflow
> +========
> +
> +Here is an example workflow for building an AutoFDO+Propeller kernel:
> +
> +1) Assuming an AutoFDO profile is already collected following
> + instructions in the AutoFDO document, build the kernel on the HOST
> + machine, with AutoFDO and Propeller build configs ::
> +
> + CONFIG_AUTOFDO_CLANG=y
> + CONFIG_PROPELLER_CLANG=y
> +
> + and ::
> +
> + $ make LLVM=1 CLANG_AUTOFDO_PROFILE=<autofdo-profile-name>
> +
> +2) Install the kernel on the TEST machine.
I am repeatedly encountered with capitalized "HOST" and "TEST".
Does this term have a special meaning instead of a test machine in general?
> +
> +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::
> +
> + $ perf record --pfm-event RETIRED_TAKEN_BRANCH_INSTRUCTIONS:k -a -N -b -c <count> -o <perf_file> -- <loadtest>
> +
> + Note you can repeat the above steps to collect multiple <perf_file>s.
> +
> +4) (Optional) Download the raw perf file(s) to the HOST machine.
> +
> +5) Use the create_llvm_prof tool (https://github.com/google/autofdo) to
> + generate Propeller profile. ::
> +
> + $ create_llvm_prof --binary=<vmlinux> --profile=<perf_file>
> + --format=propeller --propeller_output_module_name
> + --out=<propeller_profile_prefix>_cc_profile.txt
> + --propeller_symorder=<propeller_profile_prefix>_ld_profile.txt
> +
> + "<propeller_profile_prefix>" can be something like "/home/user/dir/any_string".
> +
> + This command generates a pair of Propeller profiles:
> + "<propeller_profile_prefix>_cc_profile.txt" and
> + "<propeller_profile_prefix>_ld_profile.txt".
> +
> + If there are more than 1 perf_file collected in the previous step,
> + you can create a temp list file "<perf_file_list>" with each line
> + containing one perf file name and run::
> +
> + $ create_llvm_prof --binary=<vmlinux> --profile=@<perf_file_list>
> + --format=propeller --propeller_output_module_name
> + --out=<propeller_profile_prefix>_cc_profile.txt
> + --propeller_symorder=<propeller_profile_prefix>_ld_profile.txt
> +
> +6) Rebuild the kernel using the AutoFDO and Propeller
> + profiles. ::
"." and "::" are an odd combination.
> +
> + CONFIG_AUTOFDO_CLANG=y
> + CONFIG_PROPELLER_CLANG=y
> +
> + and ::
> +
> + $ make LLVM=1 CLANG_AUTOFDO_PROFILE=<profile_file> CLANG_PROPELLER_PROFILE_PREFIX=<propeller_profile_prefix>
> diff --git a/Makefile b/Makefile
> index bbb6ec68f5dc..2d2f688c21c6 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -1019,6 +1019,7 @@ 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-$(CONFIG_PROPELLER_CLANG) += scripts/Makefile.propeller
> include-$(CONFIG_GCC_PLUGINS) += scripts/Makefile.gcc-plugins
>
> include $(addprefix $(srctree)/, $(include-y))
> diff --git a/arch/Kconfig b/arch/Kconfig
> index 5e9604960cbb..fdeb5f173a10 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -831,6 +831,28 @@ config AUTOFDO_CLANG
>
> If unsure, say N.
>
> +config ARCH_SUPPORTS_PROPELLER_CLANG
> + bool
> +
> +config PROPELLER_CLANG
> + bool "Enable Clang's Propeller build"
> + depends on ARCH_SUPPORTS_PROPELLER_CLANG
> + depends on AUTOFDO_CLANG
> + depends on CC_IS_CLANG && CLANG_VERSION >= 190000
CC_IS_CLANG is redundant, but I am fine if you want to have it explicitly.
> + help
> + This option enables Clang’s Propeller build which
> + is on top of AutoFDO build. When the Propeller profiles
> + is specified in variable CLANG_PROPELLER_PROFILE_PREFIX
> + during the build process, Clang uses the profiles to
> + optimize the kernel.
> +
> + If no profile is specified, Proepller options are
"Proepller" is a typo.
> + still passed to Clang to facilitate the collection
> + of perf data for creating the Propeller profiles 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 503a0268155a..da47164bfddc 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -127,6 +127,7 @@ config X86
> select ARCH_SUPPORTS_LTO_CLANG_THIN
> select ARCH_SUPPORTS_RT
> select ARCH_SUPPORTS_AUTOFDO_CLANG
> + select ARCH_SUPPORTS_PROPELLER_CLANG if X86_64
> select ARCH_USE_BUILTIN_BSWAP
> select ARCH_USE_CMPXCHG_LOCKREF if X86_CMPXCHG64
> select ARCH_USE_MEMTEST
> diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
> index 6726be89b7a6..7ecc21c569be 100644
> --- a/arch/x86/kernel/vmlinux.lds.S
> +++ b/arch/x86/kernel/vmlinux.lds.S
> @@ -442,6 +442,10 @@ SECTIONS
>
> STABS_DEBUG
> DWARF_DEBUG
> +#ifdef CONFIG_PROPELLER_CLANG
> + .llvm_bb_addr_map : { *(.llvm_bb_addr_map) }
> +#endif
> +
> ELF_DETAILS
>
> DISCARDS
> diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
> index 20e46c0917db..5986dd4cfb14 100644
> --- a/include/asm-generic/vmlinux.lds.h
> +++ b/include/asm-generic/vmlinux.lds.h
> @@ -95,14 +95,14 @@
> * With LTO_CLANG, the linker also splits sections by default, so we need
> * these macros to combine the sections during the final link.
> *
> - * With LTO_CLANG, the linker also splits sections by default, so we need
> - * these macros to combine the sections during the final link.
> + * CONFIG_AUTOFD_CLANG and CONFIG_PROPELLER_CLANG will also split text sections
> + * and cluster them in the linking time.
> *
> * RODATA_MAIN is not used because existing code already defines .rodata.x
> * sections to be brought in with rodata.
> */
> #if defined(CONFIG_LD_DEAD_CODE_DATA_ELIMINATION) || defined(CONFIG_LTO_CLANG) || \
> -defined(CONFIG_AUTOFDO_CLANG)
> +defined(CONFIG_AUTOFDO_CLANG) || defined(CONFIG_PROPELLER_CLANG)
If you have "depends on PROPELLER_CLANG" in Kconfig,
you do not need to touch this line.
When CONFIG_PROPELLER_CLANG is enabled, CONFIG_AUTOFDO_CLANG is already defined.
> #define TEXT_MAIN .text .text.[0-9a-zA-Z_]*
> #else
> #define TEXT_MAIN .text
> @@ -556,7 +556,7 @@ defined(CONFIG_AUTOFDO_CLANG)
> __cpuidle_text_end = .; \
> __noinstr_text_end = .;
>
> -#ifdef CONFIG_AUTOFDO_CLANG
> +#if defined(CONFIG_AUTOFDO_CLANG) || defined(CONFIG_PROPELLER_CLANG)
Ditto.
> #define TEXT_HOT \
> __hot_text_start = .; \
> *(.text.hot .text.hot.*) \
> @@ -584,7 +584,7 @@ defined(CONFIG_AUTOFDO_CLANG)
> * first when in these builds.
> */
> #if defined(CONFIG_LD_DEAD_CODE_DATA_ELIMINATION) || defined(CONFIG_LTO_CLANG) || \
> -defined(CONFIG_AUTOFDO_CLANG)
> +defined(CONFIG_AUTOFDO_CLANG) || defined(CONFIG_PROPELLER_CLANG)
Ditto.
Make sense only when CONFIG_AUTOFDO_CLANG and CONFIG_PROPELLER_CLANG
are independent of each other.
> #define TEXT_TEXT \
> ALIGN_FUNCTION(); \
> *(.text.asan.* .text.tsan.*) \
> diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
> index e85d6ac31bd9..60354c476956 100644
> --- a/scripts/Makefile.lib
> +++ b/scripts/Makefile.lib
> @@ -201,6 +201,16 @@ _c_flags += $(if $(patsubst n%,, \
> $(CFLAGS_AUTOFDO_CLANG))
> endif
>
> +#
> +# Enable Clang's Propeller build flags for a file or directory depending on
> +# variables AUTOFDO_PROPELLER_obj.o and PROPELLER_PROFILE.
The same comment as in 1/6.
> +#
> +ifeq ($(CONFIG_PROPELLER_CLANG),y)
ifdef CONFIG_PROPELLER_CLANG
would be simpler, as you used this style in scripts/Makefile.propeller
> +_c_flags += $(if $(patsubst n%,, \
> + $(AUTOFDO_PROFILE_$(target-stem).o)$(AUTOFDO_PROFILE)$(PROPELLER_PROFILE))$(is-kernel-object), \
> + $(CFLAGS_PROPELLER_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/scripts/Makefile.propeller b/scripts/Makefile.propeller
> new file mode 100644
> index 000000000000..344190717e47
> --- /dev/null
> +++ b/scripts/Makefile.propeller
> +# Propeller requires debug information to embed module names in the profiles.
> +# If CONFIG_DEBUG_INFO is not enabled, set -gmlt option. Skip this for AutoFDO,
> +# as the option should already be set.
> +ifndef CONFIG_DEBUG_INFO
> + ifndef CONFIG_AUTOFDO_CLANG
> + CFLAGS_PROPELLER_CLANG += -gmlt
> + endif
> +endif
This block is dead code due to "depends on AUTOFDO_CLANG".
"ifndef CONFIG_AUTOFDO_CLANG" is never met here.
--
Best Regards
Masahiro Yamada
On Sun, Oct 20, 2024 at 10:49 AM Masahiro Yamada <masahiroy@kernel.org> wrote:
>
> Please remove the period at the end of the commit subject.
Will fix this.
>
>
>
> On Tue, Oct 15, 2024 at 6:34 AM Rong Xu <xur@google.com> wrote:
> >
> > Add the build support for using Clang's Propeller optimizer. Like
> > AutoFDO, Propeller 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.
> >
> > The support requires a Clang compiler LLVM 19 or later, and the
> > create_llvm_prof tool
> > (https://github.com/google/autofdo/releases/tag/v0.30.1). This
> > submission is limited to x86 platforms that support PMU features
>
>
> "This submission" -> "This commit"
Will fix this.
>
>
>
> > like LBR on Intel machines and AMD Zen3 BRS.
> >
> > For Arm, we plan to send patches for SPE-based Propeller when
> > AutoFDO for Arm is ready.
>
>
> "we plan to send ..." is not a good description once it is committed.
>
> This sentence should be moved to the cover letter, or reworked.
We will move this sentence to the cover letter.
>
>
>
>
>
>
> >
> > Here is an example workflow for building an AutoFDO+Propeller
> > optimized kernel:
> >
> > 1) Build the kernel on the HOST machine, with AutoFDO and Propeller
>
>
> Why is the "HOST" capitalized?
We will fix this.
>
>
>
> > build config
> > CONFIG_AUTOFDO_CLANG=y
> > CONFIG_PROPELLER_CLANG=y
> > then
> > $ make LLVM=1 CLANG_AUTOFDO_PROFILE=<autofdo_profile>
> >
> > “<autofdo_profile>” is the profile collected when doing a non-Propeller
> > AutoFDO build. This step builds a kernel that has the same optimization
> > level as AutoFDO, plus a metadata section that records basic block
> > information. This kernel image runs as fast as an AutoFDO optimized
> > kernel.
> >
> > 2) Install the kernel on test/production machines.
> >
> > 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
> > # To see if Zen3 support LBR:
> > $ cat proc/cpuinfo | grep " brs"
> > # To see if Zen4 support LBR:
> > $ cat proc/cpuinfo | grep amd_lbr_v2
> > # If the result is yes, then collect the profile using:
> > $ 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.
>
>
> Same question as above.
Will use "host".
>
>
> >
> > 5) Generate Propeller profile:
> > $ create_llvm_prof --binary=<vmlinux> --profile=<perf_file> \
> > --format=propeller --propeller_output_module_name \
> > --out=<propeller_profile_prefix>_cc_profile.txt \
> > --propeller_symorder=<propeller_profile_prefix>_ld_profile.txt
> >
> > “create_llvm_prof” is the profile conversion tool, and a prebuilt
> > binary for linux can be found on
> > https://github.com/google/autofdo/releases/tag/v0.30.1 (can also build
> > from source).
> >
> > "<propeller_profile_prefix>" can be something like
> > "/home/user/dir/any_string".
> >
> > This command generates a pair of Propeller profiles:
> > "<propeller_profile_prefix>_cc_profile.txt" and
> > "<propeller_profile_prefix>_ld_profile.txt".
> >
> > 6) Rebuild the kernel using the AutoFDO and Propeller profile files.
> > CONFIG_AUTOFDO_CLANG=y
> > CONFIG_PROPELLER_CLANG=y
> > and
> > $ make LLVM=1 CLANG_AUTOFDO_PROFILE=<autofdo_profile> \
> > CLANG_PROPELLER_PROFILE_PREFIX=<propeller_profile_prefix>
> >
> > 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>
>
>
>
> >
> > .. only:: subproject and html
> > diff --git a/Documentation/dev-tools/propeller.rst b/Documentation/dev-tools/propeller.rst
> > new file mode 100644
> > index 000000000000..a217354e0f95
> > --- /dev/null
> > +++ b/Documentation/dev-tools/propeller.rst
> > @@ -0,0 +1,161 @@
> > +.. SPDX-License-Identifier: GPL-2.0
> > +
> > +=====================================
> > +Using Propeller with the Linux kernel
> > +=====================================
> > +
> > +This enables Propeller build support for the kernel when using Clang
> > +compiler. Propeller is a profile-guided optimization (PGO) method used
> > +to optimize binary executables. Like AutoFDO, it utilizes hardware
> > +sampling to gather information about the frequency of execution of
> > +different code paths within a binary. Unlike AutoFDO, this information
> > +is then used right before linking phase to optimize (among others)
> > +block layout within and across functions.
> > +
> > +A few important notes about adopting Propeller optimization:
> > +
> > +#. Although it can be used as a standalone optimization step, it is
> > + strongly recommended to apply Propeller on top of AutoFDO,
> > + AutoFDO+ThinLTO or Instrument FDO. The rest of this document
> > + assumes this paradigm.
>
> This is a hard requirement instead of a recommendation
> because PROPERLLER_CLANG has "depends on AUTOFDO_CLANG".
Actually PROPELLER_CLANG does not depend on AUTOFDO_CLANG.
We should apply Propeller on top of the vanilla build kernel.
I admit that we did not do a good job to separate these two in this patch.
>
>
>
>
> > +
> > +#. Propeller uses another round of profiling on top of
> > + AutoFDO/AutoFDO+ThinLTO/iFDO. The whole build process involves
> > + "build-afdo - train-afdo - build-propeller - train-propeller -
> > + build-optimized".
> > +
> > +#. Propeller requires LLVM 19 release or later for Clang/Clang++
> > + and the linker(ld.lld).
> > +
> > +#. In addition to LLVM toolchain, Propeller requires a profiling
> > + conversion tool: https://github.com/google/autofdo with a release
> > + after v0.30.1: https://github.com/google/autofdo/releases/tag/v0.30.1.
> > +
> > +The Propeller optimization process involves the following steps:
> > +
> > +#. Initial building: Build the AutoFDO or AutoFDO+ThinLTO binary as
> > + you would normally do, but with a set of compile-time / link-time
> > + flags, so that a special metadata section is created within the
> > + kernel binary. The special section is only intend to be used by the
> > + profiling tool, it is not part of the runtime image, nor does it
> > + change kernel run time text sections.
> > +
> > +#. 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. Propeller is most effective on
> > + platforms supporting advanced PMU features like LBR on Intel
> > + machines. This step is the same as profiling the kernel for AutoFDO
> > + (the exact perf parameters can be different).
> > +
> > +#. Propeller profile generation: Perf output file is converted to a
> > + pair of Propeller profiles via an offline tool.
> > +
> > +#. Optimized build: Build the AutoFDO or AutoFDO+ThinLTO optimized
> > + binary as you would normally do, but with a compile-time /
> > + link-time flag to pick up the Propeller compile time and link time
> > + profiles. This build step uses 3 profiles - the AutoFDO profile,
> > + the Propeller compile-time profile and the Propeller link-time
> > + profile.
> > +
> > +#. Deployment: The optimized kernel binary is deployed and used
> > + in production environments, providing improved performance
> > + and reduced latency.
> > +
> > +Preparation
> > +===========
> > +
> > +Configure the kernel with::
> > +
> > + CONFIG_AUTOFDO_CLANG=y
>
>
> This is automatically met due to "depends on AUTOFDO_CLANG".
Agreed. But we will remove the dependency from PROPELlER_CLANG to AUTOFDO_CLANG.
So we will keep the part.
>
>
>
> > + CONFIG_PROPELLER_CLANG=y
> > +
> > +Customization
> > +=============
> > +
> > +You can enable or disable Propeller build for individual file and
> > +directories by adding a line similar to the following to the
> > +respective kernel Makefile:
>
> The same comment as in 1/6.
We will fix this similar to the proposed change in 1/6 if you think
the change there is acceptable.
>
>
>
> > +- For enabling a single file (e.g. foo.o)::
> > +
> > + PROPELLER_PROFILE_foo.o := y
> > +
> > +- For enabling all files in one directory::
> > +
> > + PROPELLER_PROFILE := y
> > +
> > +- For disabling one file::
> > +
> > + PROPELLER_PROFILE_foo.o := n
> > +
> > +- For disabling all files in one directory::
> > +
> > + PROPELLER__PROFILE := n
> > +
> > +
> > +Workflow
> > +========
> > +
> > +Here is an example workflow for building an AutoFDO+Propeller kernel:
> > +
> > +1) Assuming an AutoFDO profile is already collected following
> > + instructions in the AutoFDO document, build the kernel on the HOST
> > + machine, with AutoFDO and Propeller build configs ::
> > +
> > + CONFIG_AUTOFDO_CLANG=y
> > + CONFIG_PROPELLER_CLANG=y
> > +
> > + and ::
> > +
> > + $ make LLVM=1 CLANG_AUTOFDO_PROFILE=<autofdo-profile-name>
> > +
> > +2) Install the kernel on the TEST machine.
>
>
> I am repeatedly encountered with capitalized "HOST" and "TEST".
>
> Does this term have a special meaning instead of a test machine in general?
No special meaning. This is not intentional. Will fix this.
>
>
>
>
>
>
>
> > +
> > +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::
> > +
> > + $ perf record --pfm-event RETIRED_TAKEN_BRANCH_INSTRUCTIONS:k -a -N -b -c <count> -o <perf_file> -- <loadtest>
> > +
> > + Note you can repeat the above steps to collect multiple <perf_file>s.
> > +
> > +4) (Optional) Download the raw perf file(s) to the HOST machine.
> > +
> > +5) Use the create_llvm_prof tool (https://github.com/google/autofdo) to
> > + generate Propeller profile. ::
> > +
> > + $ create_llvm_prof --binary=<vmlinux> --profile=<perf_file>
> > + --format=propeller --propeller_output_module_name
> > + --out=<propeller_profile_prefix>_cc_profile.txt
> > + --propeller_symorder=<propeller_profile_prefix>_ld_profile.txt
> > +
> > + "<propeller_profile_prefix>" can be something like "/home/user/dir/any_string".
> > +
> > + This command generates a pair of Propeller profiles:
> > + "<propeller_profile_prefix>_cc_profile.txt" and
> > + "<propeller_profile_prefix>_ld_profile.txt".
> > +
> > + If there are more than 1 perf_file collected in the previous step,
> > + you can create a temp list file "<perf_file_list>" with each line
> > + containing one perf file name and run::
> > +
> > + $ create_llvm_prof --binary=<vmlinux> --profile=@<perf_file_list>
> > + --format=propeller --propeller_output_module_name
> > + --out=<propeller_profile_prefix>_cc_profile.txt
> > + --propeller_symorder=<propeller_profile_prefix>_ld_profile.txt
> > +
> > +6) Rebuild the kernel using the AutoFDO and Propeller
> > + profiles. ::
>
>
> "." and "::" are an odd combination.
"::" is an rst marker. I will make sure the rendered text looks good.
>
>
>
>
> > +
> > + CONFIG_AUTOFDO_CLANG=y
> > + CONFIG_PROPELLER_CLANG=y
> > +
> > + and ::
> > +
> > + $ make LLVM=1 CLANG_AUTOFDO_PROFILE=<profile_file> CLANG_PROPELLER_PROFILE_PREFIX=<propeller_profile_prefix>
>
>
>
> > diff --git a/Makefile b/Makefile
> > index bbb6ec68f5dc..2d2f688c21c6 100644
> > --- a/Makefile
> > +++ b/Makefile
> > @@ -1019,6 +1019,7 @@ 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-$(CONFIG_PROPELLER_CLANG) += scripts/Makefile.propeller
> > include-$(CONFIG_GCC_PLUGINS) += scripts/Makefile.gcc-plugins
> >
> > include $(addprefix $(srctree)/, $(include-y))
> > diff --git a/arch/Kconfig b/arch/Kconfig
> > index 5e9604960cbb..fdeb5f173a10 100644
> > --- a/arch/Kconfig
> > +++ b/arch/Kconfig
> > @@ -831,6 +831,28 @@ config AUTOFDO_CLANG
> >
> > If unsure, say N.
> >
> > +config ARCH_SUPPORTS_PROPELLER_CLANG
> > + bool
> > +
> > +config PROPELLER_CLANG
> > + bool "Enable Clang's Propeller build"
> > + depends on ARCH_SUPPORTS_PROPELLER_CLANG
> > + depends on AUTOFDO_CLANG
> > + depends on CC_IS_CLANG && CLANG_VERSION >= 190000
>
>
> CC_IS_CLANG is redundant, but I am fine if you want to have it explicitly.
Let's keep this just for clarity purposes.
>
>
>
> > + help
> > + This option enables Clang’s Propeller build which
> > + is on top of AutoFDO build. When the Propeller profiles
> > + is specified in variable CLANG_PROPELLER_PROFILE_PREFIX
> > + during the build process, Clang uses the profiles to
> > + optimize the kernel.
> > +
> > + If no profile is specified, Proepller options are
>
>
> "Proepller" is a typo.
Thanks! Will fix this.
>
>
>
>
> > + still passed to Clang to facilitate the collection
> > + of perf data for creating the Propeller profiles 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 503a0268155a..da47164bfddc 100644
> > --- a/arch/x86/Kconfig
> > +++ b/arch/x86/Kconfig
> > @@ -127,6 +127,7 @@ config X86
> > select ARCH_SUPPORTS_LTO_CLANG_THIN
> > select ARCH_SUPPORTS_RT
> > select ARCH_SUPPORTS_AUTOFDO_CLANG
> > + select ARCH_SUPPORTS_PROPELLER_CLANG if X86_64
> > select ARCH_USE_BUILTIN_BSWAP
> > select ARCH_USE_CMPXCHG_LOCKREF if X86_CMPXCHG64
> > select ARCH_USE_MEMTEST
> > diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
> > index 6726be89b7a6..7ecc21c569be 100644
> > --- a/arch/x86/kernel/vmlinux.lds.S
> > +++ b/arch/x86/kernel/vmlinux.lds.S
> > @@ -442,6 +442,10 @@ SECTIONS
> >
> > STABS_DEBUG
> > DWARF_DEBUG
> > +#ifdef CONFIG_PROPELLER_CLANG
> > + .llvm_bb_addr_map : { *(.llvm_bb_addr_map) }
> > +#endif
> > +
> > ELF_DETAILS
> >
> > DISCARDS
> > diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
> > index 20e46c0917db..5986dd4cfb14 100644
> > --- a/include/asm-generic/vmlinux.lds.h
> > +++ b/include/asm-generic/vmlinux.lds.h
> > @@ -95,14 +95,14 @@
> > * With LTO_CLANG, the linker also splits sections by default, so we need
> > * these macros to combine the sections during the final link.
> > *
> > - * With LTO_CLANG, the linker also splits sections by default, so we need
> > - * these macros to combine the sections during the final link.
> > + * CONFIG_AUTOFD_CLANG and CONFIG_PROPELLER_CLANG will also split text sections
> > + * and cluster them in the linking time.
> > *
> > * RODATA_MAIN is not used because existing code already defines .rodata.x
> > * sections to be brought in with rodata.
> > */
> > #if defined(CONFIG_LD_DEAD_CODE_DATA_ELIMINATION) || defined(CONFIG_LTO_CLANG) || \
> > -defined(CONFIG_AUTOFDO_CLANG)
> > +defined(CONFIG_AUTOFDO_CLANG) || defined(CONFIG_PROPELLER_CLANG)
>
>
> If you have "depends on PROPELLER_CLANG" in Kconfig,
> you do not need to touch this line.
>
> When CONFIG_PROPELLER_CLANG is enabled, CONFIG_AUTOFDO_CLANG is already defined.
We will remove the dependency from CONFIG_PROPELLER_CLANG to
CONFIG_AUTOFDO_CLANG.
So I guess we will keep this part.
>
>
>
>
> > #define TEXT_MAIN .text .text.[0-9a-zA-Z_]*
> > #else
> > #define TEXT_MAIN .text
> > @@ -556,7 +556,7 @@ defined(CONFIG_AUTOFDO_CLANG)
> > __cpuidle_text_end = .; \
> > __noinstr_text_end = .;
> >
> > -#ifdef CONFIG_AUTOFDO_CLANG
> > +#if defined(CONFIG_AUTOFDO_CLANG) || defined(CONFIG_PROPELLER_CLANG)
>
>
> Ditto.
>
>
> > #define TEXT_HOT \
> > __hot_text_start = .; \
> > *(.text.hot .text.hot.*) \
> > @@ -584,7 +584,7 @@ defined(CONFIG_AUTOFDO_CLANG)
> > * first when in these builds.
> > */
> > #if defined(CONFIG_LD_DEAD_CODE_DATA_ELIMINATION) || defined(CONFIG_LTO_CLANG) || \
> > -defined(CONFIG_AUTOFDO_CLANG)
> > +defined(CONFIG_AUTOFDO_CLANG) || defined(CONFIG_PROPELLER_CLANG)
>
>
> Ditto.
> Make sense only when CONFIG_AUTOFDO_CLANG and CONFIG_PROPELLER_CLANG
> are independent of each other.
We will make CONFIG_AUTOFDO_CLANG and CONFIG_PROPELLER_CLANG
independent of each other.
>
>
>
> > #define TEXT_TEXT \
> > ALIGN_FUNCTION(); \
> > *(.text.asan.* .text.tsan.*) \
> > diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
> > index e85d6ac31bd9..60354c476956 100644
> > --- a/scripts/Makefile.lib
> > +++ b/scripts/Makefile.lib
> > @@ -201,6 +201,16 @@ _c_flags += $(if $(patsubst n%,, \
> > $(CFLAGS_AUTOFDO_CLANG))
> > endif
> >
> > +#
> > +# Enable Clang's Propeller build flags for a file or directory depending on
> > +# variables AUTOFDO_PROPELLER_obj.o and PROPELLER_PROFILE.
>
> The same comment as in 1/6.
Will fix this.
>
>
>
> > +#
> > +ifeq ($(CONFIG_PROPELLER_CLANG),y)
>
>
>
> ifdef CONFIG_PROPELLER_CLANG
>
> would be simpler, as you used this style in scripts/Makefile.propeller
Will use the suggested code.
>
>
>
>
>
>
> > +_c_flags += $(if $(patsubst n%,, \
> > + $(AUTOFDO_PROFILE_$(target-stem).o)$(AUTOFDO_PROFILE)$(PROPELLER_PROFILE))$(is-kernel-object), \
> > + $(CFLAGS_PROPELLER_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/scripts/Makefile.propeller b/scripts/Makefile.propeller
> > new file mode 100644
> > index 000000000000..344190717e47
> > --- /dev/null
> > +++ b/scripts/Makefile.propeller
>
>
> > +# Propeller requires debug information to embed module names in the profiles.
> > +# If CONFIG_DEBUG_INFO is not enabled, set -gmlt option. Skip this for AutoFDO,
> > +# as the option should already be set.
> > +ifndef CONFIG_DEBUG_INFO
> > + ifndef CONFIG_AUTOFDO_CLANG
> > + CFLAGS_PROPELLER_CLANG += -gmlt
> > + endif
> > +endif
>
>
> This block is dead code due to "depends on AUTOFDO_CLANG".
>
> "ifndef CONFIG_AUTOFDO_CLANG" is never met here.
Yes. I think we still need to when we remove the dependency to
CONFIG_AUTOFDO_CLANG.
>
>
>
>
>
>
>
> --
> Best Regards
> Masahiro Yamada
On Tue, Oct 22, 2024 at 9:00 AM Rong Xu <xur@google.com> wrote: > > > +=========== > > > + > > > +Configure the kernel with:: > > > + > > > + CONFIG_AUTOFDO_CLANG=y > > > > > > This is automatically met due to "depends on AUTOFDO_CLANG". > > Agreed. But we will remove the dependency from PROPELlER_CLANG to AUTOFDO_CLANG. > So we will keep the part. You can replace "depends on AUTOFDO_CLANG" with "imply AUTOFDO_CLANG" if it is sensible. Up to you. -- Best Regards Masahiro Yamada
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