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

[Evgeny Voevodin]

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.

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