lkml.org 
[lkml]   [2011]   [Aug]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: x86 memcpy performance
On Mon, Aug 15, 2011 at 10:34:35PM -0400, Valdis.Kletnieks@vt.edu wrote:
> On Sun, 14 Aug 2011 11:59:10 +0200, Borislav Petkov said:
>
> > Benchmarking with 10000 iterations, average results:
> > size XM MM speedup
> > 119 540.58 449.491 0.8314969419
>
> > 12273 2307.86 4042.88 1.751787902
> > 13924 2431.8 4224.48 1.737184756
> > 14335 2469.4 4218.82 1.708440514
> > 15018 2675.67 1904.07 0.711622886
> > 16374 2989.75 5296.26 1.771470902
> > 24564 4262.15 7696.86 1.805863077
> > 27852 4362.53 3347.72 0.7673805572
> > 28672 5122.8 7113.14 1.388524413
> > 30033 4874.62 8740.04 1.792967931
>
> The numbers for 15018 and 27852 are *way* odd for the MM case. I don't feel
> really good about this till we understand what happened for those two cases.

Yep.

> Also, anytime I see "10000 iterations", I ask myself if the benchmark
> rigging took proper note of hot/cold cache issues. That *may* explain
> the two oddball results we see above - but not knowing more about how
> it was benched, it's hard to say.

Yeah, the more scrutiny this gets the better. So I've cleaned up my
setup and have attached it.

xm_mem.c does the benchmarking and in bench_memcpy() there's the
sse_memcpy call which is the SSE memcpy implementation using inline asm.
It looks like gcc produces pretty crappy code here because if I replace
the sse_memcpy call with xm_memcpy() from xm_memcpy.S - this is the
same function but in pure asm - I get much better numbers, sometimes
even over 2x. It all depends on the alignment of the buffers though.
Also, those numbers don't include the context saving/restoring which the
kernel does for us.

7491 1509.89 2346.94 1.554378381
8170 2166.81 2857.78 1.318890326
12277 2659.03 4179.31 1.571744176
13907 2571.24 4125.7 1.604558427
14319 2638.74 5799.67 2.19789466 <----
14993 2752.42 4413.85 1.603625603
16371 3479.11 5562.65 1.59887055

So please take a look and let me know what you think.

Thanks.

--
Regards/Gruss,
Boris.

Advanced Micro Devices GmbH
Einsteinring 24, 85609 Dornach
GM: Alberto Bozzo
Reg: Dornach, Landkreis Muenchen
HRB Nr. 43632 WEEE Registernr: 129 19551
[unhandled content-type:application/octet-stream]
\
 
 \ /
  Last update: 2011-08-16 14:19    [W:0.116 / U:2.756 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site