Re: [Qemu-devel] [RFC v4 00/28] Base enabling patches for MTTCG

[Alex Bennée]

On 11 August 2016 at 17:43, G 3 <address@hidden> wrote:
>
> On Aug 11, 2016, at 11:24 AM, address@hidden wrote:
>
>
> Performance
>
> ===========
>
>
> You can't do full work-load testing on this tree due to the lack of
>
> atomic support (but I will run some numbers on
>
> mttcg/base-patches-v4-with-cmpxchg-atomics-v2). However you certainly
>
> see a run time improvement with the kvm-unit-tests TCG group.
>
>
>   retry.py called with ['./run_tests.sh', '-t', '-g', 'tcg', '-o', '-accel
> tcg,thread=single']
>
>   run 1: ret=0 (PASS), time=1047.147924 (1/1)
>
>   run 2: ret=0 (PASS), time=1071.921204 (2/2)
>
>   run 3: ret=0 (PASS), time=1048.141600 (3/3)
>
>   Results summary:
>
>   0: 3 times (100.00%), avg time 1055.737 (196.70 varience/14.02 deviation)
>
>   Ran command 3 times, 3 passes
>
>   retry.py called with ['./run_tests.sh', '-t', '-g', 'tcg', '-o', '-accel
> tcg,thread=multi']
>
>   run 1: ret=0 (PASS), time=303.074210 (1/1)
>
>   run 2: ret=0 (PASS), time=304.574991 (2/2)
>
>   run 3: ret=0 (PASS), time=303.327408 (3/3)
>
>   Results summary:
>
>   0: 3 times (100.00%), avg time 303.659 (0.65 varience/0.80 deviation)
>
>   Ran command 3 times, 3 passes
>
>
> The TCG tests run with -smp 4 on my system. While the TCG tests are
>
> purely CPU bound they do exercise the hot and cold paths of TCG
>
> execution (especially when triggering SMC detection). However there is
>
> still a benefit even with a 50% overhead compared to the ideal 263
>
> second elapsed time.
>
>
> Alex
>
>
>
> Your tests results look very promising. It looks like you saw a 3x speed
> improvement over single threading. Excellent. I wonder what the numbers
> would be for a 22 core Xeon or 72 core Xeon Phi...

Well the initial results look like they tail off but I need to test on a more
capable machine. I'm going to package up the test case first so people
can easily
replicate the test.

> Do you think you could some test with an x86 guest like Windows XP? There
> are plenty of benchmark tests for this platform. Video encoding, Youtube
> video playback, and number crunching programs' results would be very
> interesting to see.

I don't have any Windows images to hand I'm afraid. Besides Windows is a fairly
boring guest from this point of view because:

  - it's x86, so why use TCG over KVM
  - QEMU TCG generally sucks at media bencmarks due to SIMD emulation

-- 
Alex Bennée
KVM/QEMU Hacker for Linaro