Re: [Qemu-devel] [PATCH v2 0/7] TCG global variables clean-up

[Blue Swirl]

On Fri, Oct 26, 2012 at 6:32 AM, Evgeny Voevodin <address@hidden> wrote:
> Today I made more precise testing with usage of --enable-profiler.
>
> Here is the test procedure:
> 1. Boot Linux Kernel 5 times.
> 2. For each iteration wait while "JIT cycles" is stable for ~10 seconds
> 3. Write down the "cycles/op"
>
> Here are the results:
>
> Before clean-up:
> min: 731.9
> max: 735.8
> avg: 734.3
> standard deviation: ~2 = 0.3%
> Avarage cycles/op = 734 +- 2
>
> After clean-up:
> min: 747.2
> max: 751.7
> avg: 750.5
> standard deviation: ~2 = 0.3%
> Avarage cycles/op = 750 +- 2
> Slow-down of TCG code generation = 2.2%
>
>
> After clean-up with TCGContext *const tcg_cur_ctx:
> min: 730.6
> max: 733.2
> avg: 728.7
> standard deviation: ~2 = 0.3%
> Avarage cycles/op = 729 +- 2
> Slow-down of TCG code generation = 0%
>
> I suggest to define tcg_cur_ctx as TCGContext *const.
> Then we will get rid of TCG code generation slow-down and also
> will have no usage of global variables.

How does this compare with the original version without pointers? I
think that version may be safer to be assumed to be optimized by the
compiler.

>
>
> On 10/25/2012 10:45 AM, Evgeny Voevodin wrote:
>>
>> Here are the results of tests before and after this patch series was
>> applied:
>>
>> * EEMBC CoreMark (before -> after)
>>    - Guest: Exynos4210 ARMv7, Linux (Custom buildroot image)
>>    - Host: Intel(R) Core(TM) i5 CPU 750 @ 2.67GHz, 4GB RAM, Linux
>>    - Results: 1148.105626 -> 1161.440186 (+1.16%)
>>
>> * nbench (before -> after)
>>    - Guest: Exynos4210 ARMv7, Linux (Custom buildroot image)
>>    - Host: Intel(R) Core(TM) i5 CPU 750 @ 2.67GHz, 4GB RAM, Linux
>>    - Results
>>      . MEMORY INDEX: 1.864 -> 1.862 (-0.11%)
>>      . INTEGER INDEX: 2.518 -> 2.523 (+0.2%)
>>      . FLOATING-POINT INDEX: 0.385 -> 0.394 (+2.34%)
>>
>>
>> Those tests show that it became even faster :))
>>
>> But I'm quite sceptical about such results.
>> The thing is that in case of nbench it prints the warning if results are
>> not 95% statistically accurate.
>> So we can be sure that nbench result is 95% accurate.
>> And it's obvious that result shown above are in the scope of this
>> accuracy.
>> I don't know the accuracy of CoreMark.
>>
>> So, the main decision we can make that this patch series didn't
>> introduce any slow-down comparable to inaccuracy of the measurement.
>>
>> Is this enough?
>>
>> On 10/23/2012 10:21 AM, Evgeny Voevodin wrote:
>>>
>>> This set of patches moves global variables to tcg_ctx:
>>> gen_opc_ptr
>>> gen_opparam_ptr
>>> gen_opc_buf
>>> gen_opparam_buf
>>>
>>> Build tested for all targets.
>>> Execution tested on ARM.
>>>
>>> I didn't notice any slow-down of kernel boot after this set was applied.
>>>
>>> Changelog:
>>> v1->v2:
>>> Introduced TCGContext *tcg_cur_ctx global to use in those places where
>>> we don't
>>> have an interface to pass pointer to tcg_ctx.
>>> Code style clean-up
>>>
>>> Evgeny (2):
>>>    tcg/tcg.h: Duplicate global TCG variables in TCGContext
>>>    TCG: Remove unused global variables
>>>
>>> Evgeny Voevodin (5):
>>>    translate-all.c: Introduce TCGContext *tcg_cur_ctx
>>>    TCG: Use gen_opc_ptr from context instead of global variable.
>>>    TCG: Use gen_opparam_ptr from context instead of global variable.
>>>    TCG: Use gen_opc_buf from context instead of global variable.
>>>    TCG: Use gen_opparam_buf from context instead of global variable.
>>>
>>>   gen-icount.h                  |    2 +-
>>>   target-alpha/translate.c      |   10 +-
>>>   target-arm/translate.c        |   10 +-
>>>   target-cris/translate.c       |   13 +-
>>>   target-i386/translate.c       |   10 +-
>>>   target-lm32/translate.c       |   13 +-
>>>   target-m68k/translate.c       |   10 +-
>>>   target-microblaze/translate.c |   13 +-
>>>   target-mips/translate.c       |   11 +-
>>>   target-openrisc/translate.c   |   13 +-
>>>   target-ppc/translate.c        |   11 +-
>>>   target-s390x/translate.c      |   11 +-
>>>   target-sh4/translate.c        |   10 +-
>>>   target-sparc/translate.c      |   10 +-
>>>   target-unicore32/translate.c  |   10 +-
>>>   target-xtensa/translate.c     |    8 +-
>>>   tcg/optimize.c                |   62 ++++----
>>>   tcg/tcg-op.h                  |  324
>>> ++++++++++++++++++++---------------------
>>>   tcg/tcg.c                     |   85 ++++++-----
>>>   tcg/tcg.h                     |   11 +-
>>>   translate-all.c               |    4 +-
>>>   21 files changed, 328 insertions(+), 323 deletions(-)
>>>
>>
>>
>
>
> --
> Kind regards,
> Evgeny Voevodin,
> Technical Leader,
> Mobile Group,
> Samsung Moscow Research Center,
> e-mail: address@hidden