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

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Date:	Mon, 01 Nov 2010 14:36:38 +0900
From:	Hitoshi Mitake <mitake@....info.waseda.ac.jp>
To:	Ingo Molnar <mingo@...e.hu>
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

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.

>
>> # 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.

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?

Thanks,
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