linux-kernel - Re: [PATCH 2/2] perf bench: add x86-64 specific benchmarks to perf bench mem memcpy

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Date:	Mon, 1 Nov 2010 10:02:51 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Hitoshi Mitake <mitake@....info.waseda.ac.jp>
Cc:	linux-kernel@...r.kernel.org, h.mitake@...il.com,
	Ma Ling <ling.ma@...el.com>, Zhao Yakui <yakui.zhao@...el.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Paul Mackerras <paulus@...ba.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH 2/2] perf bench: add x86-64 specific benchmarks to perf
 bench mem memcpy


* Hitoshi Mitake <mitake@....info.waseda.ac.jp> wrote:

> On 2010年10月31日 04:23, Ingo Molnar wrote:
> >
> >* Hitoshi Mitake<mitake@....info.waseda.ac.jp>  wrote:
> >
> >>This patch adds new file: mem-memcpy-x86-64-asm.S
> >>for x86-64 specific memcpy() benchmarking.
> >>Added new benchmarks are,
> >>  x86-64-rep:      memcpy() implemented with rep instruction
> >>  x86-64-unrolled: unrolled memcpy()
> >>
> >>Original idea of including the source files of kernel
> >>for benchmarking is suggested by Ingo Molnar.
> >>This is more effective than write-once programs for quantitative
> >>evaluation of in-kernel, little and leaf functions called high frequently.
> >>Because perf bench is in kernel source tree and executing it
> >>on various hardwares, especially new model CPUs, is easy.
> >>
> >>This way can also be used for other functions of kernel e.g. checksum functions.
> >>
> >>Example of usage on Core i3 M330:
> >>
> >>| % ./perf bench mem memcpy -l 500MB
> >>| # Running mem/memcpy benchmark...
> >>| # Copying 500MB Bytes from 0x7f911f94c010 to 0x7f913ed4d010 ...
> >>|
> >>|      578.732506 MB/Sec
> >>| % ./perf bench mem memcpy -l 500MB -r x86-64-rep
> >>| # Running mem/memcpy benchmark...
> >>| # Copying 500MB Bytes from 0x7fb4b6fe4010 to 0x7fb4d63e5010 ...
> >>|
> >>|      738.184980 MB/Sec
> >>| % ./perf bench mem memcpy -l 500MB -r x86-64-unrolled
> >>| # Running mem/memcpy benchmark...
> >>| # Copying 500MB Bytes from 0x7f6f2e668010 to 0x7f6f4da69010 ...
> >>|
> >>|      767.483269 MB/Sec
> >>
> >>This shows clearly that unrolled memcpy() is efficient
> >>than rep version and glibc's one :)
> >
> >Hey, really cool output :-)
> >
> >Might also make sense to measure Ma Ling's patched version?
> 
> Does Ma Ling's patched version mean,
> 
> http://marc.info/?l=linux-kernel&m=128652296500989&w=2
> 
> the memcpy applied the patch of the URL?
> (It seems that this patch was written by Miao Xie.)
> 
> I'll include the result of patched version in the next post.

(Indeed it is Miao Xie - sorry!)

> >># checkpatch.pl warns about two externs in bench/mem-memcpy.c
> >># added by this patch. But I think it is no problem.
> >
> >You should put these:
> >
> >  +#ifdef ARCH_X86_64
> >  +extern void *memcpy_x86_64_unrolled(void *to, const void *from, size_t len);
> >  +extern void *memcpy_x86_64_rep(void *to, const void *from, size_t len);
> >  +#endif
> >
> >into a .h file - a new one if needed.
> >
> >That will make both checkpatch and me happier ;-)
> >
> 
> OK, I'll separate these files.
> 
> BTW, I found really interesting evaluation result.
> Current results of "perf bench mem memcpy" include
> the overhead of page faults because the measured memcpy()
> is the first access to allocated memory area.
> 
> I tested the another version of perf bench mem memcpy,
> which does memcpy() before measured memcpy() for removing
> the overhead come from page faults.
> 
> And this is the result:
> 
> % ./perf bench mem memcpy -l 500MB -r x86-64-unrolled
> # Running mem/memcpy benchmark...
> # Copying 500MB Bytes from 0x7f19d488f010 to 0x7f19f3c90010 ...
> 
>        4.608340 GB/Sec
> 
> % ./perf bench mem memcpy -l 500MB
> # Running mem/memcpy benchmark...
> # Copying 500MB Bytes from 0x7f696c3cc010 to 0x7f698b7cd010 ...
> 
>        4.856442 GB/Sec
> 
> % ./perf bench mem memcpy -l 500MB -r x86-64-rep
> # Running mem/memcpy benchmark...
> # Copying 500MB Bytes from 0x7f45d6cff010 to 0x7f45f6100010 ...
> 
>        6.024445 GB/Sec
> 
> The relation of scores reversed!
> I cannot explain the cause of this result, and
> this is really interesting phenomenon.

Interesting indeed, and it would be nice to analyse that! (It should be possible, 
using various PMU metrics in a clever way, to figure out what's happening inside the 
CPU, right?)

> So I'd like to add new command line option,
> like "--pre-page-faults" to perf bench mem memcpy,
> for doing memcpy() before measured memcpy().
> 
> How do you think about this idea?

Agreed. (Maybe name it --prefault, as 'prefaulting' is the term we generally use for 
things like this.)

An even better solution would be to output _both_ results by default, so that people 
can see both characteristics at a glance?

Thanks,

	Ingo
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