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SubjectRe: [PATCH 2/2] perf bench: add x86-64 specific benchmarks to perf bench mem memcpy
On 2010年11月01日 18:02, Ingo Molnar wrote:
>
> * Hitoshi Mitake<mitake@dcl.info.waseda.ac.jp> wrote:
>
>> On 2010年10月31日 04:23, Ingo Molnar wrote:
>>>
>>> * Hitoshi Mitake<mitake@dcl.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?)
>

I corrected the PMU information of the each case of memcpy,
below is the result:

(I used partial monitoring patch I posted before:
https://patchwork.kernel.org/patch/408801/,
and my local modification for testing rep based memcpy)

no prefault benchmarking

unrolled

Score: 685.812729 MB/Sec
Stat:
Performance counter stats for process id '4139':

725.939831 task-clock-msecs # 0.995 CPUs
74 context-switches # 0.000 M/sec
2 CPU-migrations # 0.000 M/sec
256,002 page-faults # 0.353 M/sec
1,535,468,702 cycles # 2115.146 M/sec
1,691,516,817 instructions # 1.102 IPC
291,260,006 branches # 401.218 M/sec
1,487,762 branch-misses # 0.511 %
8,470,560 cache-references # 11.668 M/sec
8,364,176 cache-misses # 11.522 M/sec

0.729488573 seconds time elapsed

rep based

Score: 670.172114 MB/Sec
Stat:
Performance counter stats for process id '5539':

742.943772 task-clock-msecs # 0.995 CPUs
77 context-switches # 0.000 M/sec
2 CPU-migrations # 0.000 M/sec
256,002 page-faults # 0.345 M/sec
1,578,787,149 cycles # 2125.043 M/sec
1,499,144,628 instructions # 0.950 IPC
275,684,806 branches # 371.071 M/sec
1,522,326 branch-misses # 0.552 %
8,503,747 cache-references # 11.446 M/sec
8,386,673 cache-misses # 11.288 M/sec

0.746320411 seconds time elapsed

prefaulted benchmarking

unrolled

Score: 4.485941 GB/Sec
Stat:
Performance counter stats for process id '4279':

108.466761 task-clock-msecs # 0.994 CPUs
11 context-switches # 0.000 M/sec
2 CPU-migrations # 0.000 M/sec
2 page-faults # 0.000 M/sec
218,260,432 cycles # 2012.233 M/sec
199,520,023 instructions # 0.914 IPC
16,963,327 branches # 156.392 M/sec
8,169 branch-misses # 0.048 %
2,955,221 cache-references # 27.245 M/sec
2,916,018 cache-misses # 26.884 M/sec

0.109115820 seconds time elapsed

rep based

Score: 5.972859 GB/Sec
Stat:
Performance counter stats for process id '5535':

81.609445 task-clock-msecs # 0.995 CPUs
8 context-switches # 0.000 M/sec
0 CPU-migrations # 0.000 M/sec
2 page-faults # 0.000 M/sec
173,888,853 cycles # 2130.744 M/sec
3,034,096 instructions # 0.017 IPC
607,897 branches # 7.449 M/sec
5,874 branch-misses # 0.966 %
8,276,533 cache-references # 101.416 M/sec
8,274,865 cache-misses # 101.396 M/sec

0.082030877 seconds time

Again, the surprising point is the reverse of the score relation.
I cannot find the direct reason of this reverse,
but it seems that the count of branch-miss is refrecting it.

I have to look into this more deeply...
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