include/exec/exec-all.h | 20 +++++++++++--------- include/exec/tb-lookup.h | 34 +++++++++++++++++----------------- accel/tcg/cpu-exec.c | 31 ++++++++++++++++++------------- accel/tcg/tcg-runtime.c | 6 ++++-- accel/tcg/translate-all.c | 14 ++++++++------ softmmu/physmem.c | 2 +- 6 files changed, 59 insertions(+), 48 deletions(-)
Hi Richard, Well I spun up some of the ideas we talked about to see if there was anything to be squeezed out of the function. In the end the results seem to be a washout with my pigz benchmark: qemu-system-aarch64 -cpu cortex-a57 \ -machine type=virt,virtualization=on,gic-version=3 \ -serial mon:stdio \ -netdev user,id=unet,hostfwd=tcp::2222-:22 \ -device virtio-net-pci,netdev=unet,id=virt-net,disable-legacy=on \ -device virtio-scsi-pci,id=virt-scsi,disable-legacy=on \ -blockdev driver=raw,node-name=hd,discard=unmap,file.driver=host_device,file.filename=/dev/zen-disk/debian-buster-arm64 \ -device scsi-hd,drive=hd,id=virt-scsi-hd \ -smp 4 -m 4096 \ -kernel ~/lsrc/linux.git/builds/arm64/arch/arm64/boot/Image \ -append "root=/dev/sda2 systemd.unit=benchmark-pigz.service" \ -display none -snapshot | Command | Mean [s] | Min [s] | Max [s] | Relative | |---------+----------------+---------+---------+----------| | Before | 46.597 ± 2.482 | 45.208 | 53.618 | 1.00 | | After | 46.867 ± 2.242 | 45.871 | 53.180 | 1.00 | Maybe the code cleanup itself makes it worthwhile. WDYT? Alex Bennée (5): accel/tcg: rename tb_lookup__cpu_state and hoist state extraction accel/tcg: move CF_CLUSTER calculation to curr_cflags accel/tcg: drop the use of CF_HASH_MASK and rename params include/exec: lightly re-arrange TranslationBlock include/exec/tb-lookup: try and reduce branch prediction issues include/exec/exec-all.h | 20 +++++++++++--------- include/exec/tb-lookup.h | 34 +++++++++++++++++----------------- accel/tcg/cpu-exec.c | 31 ++++++++++++++++++------------- accel/tcg/tcg-runtime.c | 6 ++++-- accel/tcg/translate-all.c | 14 ++++++++------ softmmu/physmem.c | 2 +- 6 files changed, 59 insertions(+), 48 deletions(-) -- 2.20.1
On 2/24/21 8:58 AM, Alex Bennée wrote:
> Hi Richard,
>
> Well I spun up some of the ideas we talked about to see if there was
> anything to be squeezed out of the function. In the end the results
> seem to be a washout with my pigz benchmark:
>
> qemu-system-aarch64 -cpu cortex-a57 \
> -machine type=virt,virtualization=on,gic-version=3 \
> -serial mon:stdio \
> -netdev user,id=unet,hostfwd=tcp::2222-:22 \
> -device virtio-net-pci,netdev=unet,id=virt-net,disable-legacy=on \
> -device virtio-scsi-pci,id=virt-scsi,disable-legacy=on \
> -blockdev driver=raw,node-name=hd,discard=unmap,file.driver=host_device,file.filename=/dev/zen-disk/debian-buster-arm64 \
> -device scsi-hd,drive=hd,id=virt-scsi-hd \
> -smp 4 -m 4096 \
> -kernel ~/lsrc/linux.git/builds/arm64/arch/arm64/boot/Image \
> -append "root=/dev/sda2 systemd.unit=benchmark-pigz.service" \
> -display none -snapshot
>
> | Command | Mean [s] | Min [s] | Max [s] | Relative |
> |---------+----------------+---------+---------+----------|
> | Before | 46.597 ± 2.482 | 45.208 | 53.618 | 1.00 |
> | After | 46.867 ± 2.242 | 45.871 | 53.180 | 1.00 |
Well that's disappointing.
> Maybe the code cleanup itself makes it worthwhile. WDYT?
I think there's little doubt that the first 3 patches are a good code cleanup.
Patch 4 I think is still beneficial, simply so that we can add that "Above
fields" comment.
Patch 5 would only be worthwhile if we could measure any positive difference,
which it seems we cannot.
I have a follow-up patch to remove the parallel_cpus global variable which I
will post in a moment. While it removes a handful of insns from this
fast-path, I doubt it helps. But getting rid of a global is probably always
positive, no?
I was glancing through the lookup function for alpha, instead of aarch64 and saw:
21e: 33 43 18 xor 0x18(%rbx),%eax
221: 4c 31 e1 xor %r12,%rcx
224: 44 31 ea xor %r13d,%edx
227: 09 c2 or %eax,%edx
229: 48 0b 4b 08 or 0x8(%rbx),%rcx
and thought -- hang on, how come we're just ORing nor XORing here? Of course
it's the cs_base field, which alpha has set to zero. The compiler has
simplified bits |= 0 ^ tb->cs_base.
Which got me thinking: what if we had a per-cpu
typedef struct {
target_ulong pc;
...
} TranslationBlockID;
static inline bool arch_tbid_cmp(TranslationBlockID x,
TranslationBlockID y)
{
return x.pc == y.pc && ...;
}
We could potentially reduce this to memcmp(&x, &y).
First, this would allow cs_base to be eliminated where it is not used. Second,
this would allow cs_base to be renamed for the non-x86 targets for which it is
being abused. Third, it would allow tb->flags to be either (a) elided or (b)
extended by the target as needed.
This final is directed at ARM, of course, where we've overflowed the uint32_t
that is tb->flags. We could now extend that to 64-bits.
Obviously, some tweaks to tb_hash_func would be required as well, but that's
manageable.
What do you think about this last?
r~
Richard Henderson <richard.henderson@linaro.org> writes:
> On 2/24/21 8:58 AM, Alex Bennée wrote:
>> Hi Richard,
>>
>> Well I spun up some of the ideas we talked about to see if there was
>> anything to be squeezed out of the function. In the end the results
>> seem to be a washout with my pigz benchmark:
>>
>> qemu-system-aarch64 -cpu cortex-a57 \
>> -machine type=virt,virtualization=on,gic-version=3 \
>> -serial mon:stdio \
>> -netdev user,id=unet,hostfwd=tcp::2222-:22 \
>> -device virtio-net-pci,netdev=unet,id=virt-net,disable-legacy=on \
>> -device virtio-scsi-pci,id=virt-scsi,disable-legacy=on \
>> -blockdev driver=raw,node-name=hd,discard=unmap,file.driver=host_device,file.filename=/dev/zen-disk/debian-buster-arm64 \
>> -device scsi-hd,drive=hd,id=virt-scsi-hd \
>> -smp 4 -m 4096 \
>> -kernel ~/lsrc/linux.git/builds/arm64/arch/arm64/boot/Image \
>> -append "root=/dev/sda2 systemd.unit=benchmark-pigz.service" \
>> -display none -snapshot
>>
>> | Command | Mean [s] | Min [s] | Max [s] | Relative |
>> |---------+----------------+---------+---------+----------|
>> | Before | 46.597 ± 2.482 | 45.208 | 53.618 | 1.00 |
>> | After | 46.867 ± 2.242 | 45.871 | 53.180 | 1.00 |
>
> Well that's disappointing.
>
>> Maybe the code cleanup itself makes it worthwhile. WDYT?
>
> I think there's little doubt that the first 3 patches are a good code cleanup.
>
> Patch 4 I think is still beneficial, simply so that we can add that "Above
> fields" comment.
>
> Patch 5 would only be worthwhile if we could measure any positive difference,
> which it seems we cannot.
>
> I have a follow-up patch to remove the parallel_cpus global variable which I
> will post in a moment. While it removes a handful of insns from this
> fast-path, I doubt it helps. But getting rid of a global is probably always
> positive, no?
>
> I was glancing through the lookup function for alpha, instead of aarch64 and saw:
>
> 21e: 33 43 18 xor 0x18(%rbx),%eax
> 221: 4c 31 e1 xor %r12,%rcx
> 224: 44 31 ea xor %r13d,%edx
> 227: 09 c2 or %eax,%edx
> 229: 48 0b 4b 08 or 0x8(%rbx),%rcx
>
> and thought -- hang on, how come we're just ORing nor XORing here? Of course
> it's the cs_base field, which alpha has set to zero. The compiler has
> simplified bits |= 0 ^ tb->cs_base.
>
> Which got me thinking: what if we had a per-cpu
>
> typedef struct {
> target_ulong pc;
> ...
> } TranslationBlockID;
>
> static inline bool arch_tbid_cmp(TranslationBlockID x,
> TranslationBlockID y)
> {
> return x.pc == y.pc && ...;
> }
>
> We could potentially reduce this to memcmp(&x, &y).
>
> First, this would allow cs_base to be eliminated where it is not used. Second,
> this would allow cs_base to be renamed for the non-x86 targets for which it is
> being abused. Third, it would allow tb->flags to be either (a) elided or (b)
> extended by the target as needed.
>
> This final is directed at ARM, of course, where we've overflowed the uint32_t
> that is tb->flags. We could now extend that to 64-bits.
>
> Obviously, some tweaks to tb_hash_func would be required as well, but that's
> manageable.
>
> What do you think about this last?
Sounds like a good idea for clean-up, especially to get rid of
cs_base/extend tbflags when needed. One concern would be where do we go
when we get to heterogeneous emulation? Will they share the same
translation area like the current cpu->cluster_index stuff or will that
only be for similar but not quite the same architectures? Maybe I'm
thinking too far ahead...
>
>
> r~
--
Alex Bennée
Patchew URL: https://patchew.org/QEMU/20210224165811.11567-1-alex.bennee@linaro.org/ Hi, This series seems to have some coding style problems. See output below for more information: Type: series Message-id: 20210224165811.11567-1-alex.bennee@linaro.org Subject: [RFC PATCH 0/5] Experimenting with tb-lookup tweaks === TEST SCRIPT BEGIN === #!/bin/bash git rev-parse base > /dev/null || exit 0 git config --local diff.renamelimit 0 git config --local diff.renames True git config --local diff.algorithm histogram ./scripts/checkpatch.pl --mailback base.. === TEST SCRIPT END === Updating 3c8cf5a9c21ff8782164d1def7f44bd888713384 From https://github.com/patchew-project/qemu - [tag update] patchew/20210218201528.127099-1-eblake@redhat.com -> patchew/20210218201528.127099-1-eblake@redhat.com - [tag update] patchew/20210224055401.492407-1-jasowang@redhat.com -> patchew/20210224055401.492407-1-jasowang@redhat.com * [new tag] patchew/20210224165811.11567-1-alex.bennee@linaro.org -> patchew/20210224165811.11567-1-alex.bennee@linaro.org * [new tag] patchew/20210224165837.21983-1-vgoyal@redhat.com -> patchew/20210224165837.21983-1-vgoyal@redhat.com - [tag update] patchew/20210225032335.64245-1-aik@ozlabs.ru -> patchew/20210225032335.64245-1-aik@ozlabs.ru * [new tag] patchew/20210225054756.35962-1-linuxmaker@163.com -> patchew/20210225054756.35962-1-linuxmaker@163.com - [tag update] patchew/20210225131316.631940-1-pbonzini@redhat.com -> patchew/20210225131316.631940-1-pbonzini@redhat.com Switched to a new branch 'test' 0be54b4 include/exec/tb-lookup: try and reduce branch prediction issues c6233de include/exec: lightly re-arrange TranslationBlock 18534bf accel/tcg: drop the use of CF_HASH_MASK and rename params 3a30caf accel/tcg: move CF_CLUSTER calculation to curr_cflags a135bea accel/tcg: rename tb_lookup__cpu_state and hoist state extraction === OUTPUT BEGIN === 1/5 Checking commit a135bea36366 (accel/tcg: rename tb_lookup__cpu_state and hoist state extraction) ERROR: "foo * bar" should be "foo *bar" #84: FILE: include/exec/tb-lookup.h:20: +static inline TranslationBlock * tb_lookup(CPUState *cpu, WARNING: line over 80 characters #85: FILE: include/exec/tb-lookup.h:21: + target_ulong pc, target_ulong cs_base, total: 1 errors, 1 warnings, 80 lines checked Patch 1/5 has style problems, please review. If any of these errors are false positives report them to the maintainer, see CHECKPATCH in MAINTAINERS. 2/5 Checking commit 3a30caf5f47d (accel/tcg: move CF_CLUSTER calculation to curr_cflags) 3/5 Checking commit 18534bff0f1f (accel/tcg: drop the use of CF_HASH_MASK and rename params) 4/5 Checking commit c6233de83263 (include/exec: lightly re-arrange TranslationBlock) WARNING: Block comments use a leading /* on a separate line #35: FILE: include/exec/exec-all.h:465: + uint16_t size; /* size of target code for this block (1 <= WARNING: Block comments use * on subsequent lines #36: FILE: include/exec/exec-all.h:466: + uint16_t size; /* size of target code for this block (1 <= + size <= TARGET_PAGE_SIZE) */ WARNING: Block comments use a trailing */ on a separate line #36: FILE: include/exec/exec-all.h:466: + size <= TARGET_PAGE_SIZE) */ total: 0 errors, 3 warnings, 20 lines checked Patch 4/5 has style problems, please review. If any of these errors are false positives report them to the maintainer, see CHECKPATCH in MAINTAINERS. 5/5 Checking commit 0be54b4ee146 (include/exec/tb-lookup: try and reduce branch prediction issues) === OUTPUT END === Test command exited with code: 1 The full log is available at http://patchew.org/logs/20210224165811.11567-1-alex.bennee@linaro.org/testing.checkpatch/?type=message. --- Email generated automatically by Patchew [https://patchew.org/]. Please send your feedback to patchew-devel@redhat.com
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