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

[Hitoshi Mitake]

On 2010å11æ01æ 18:02, Ingo Molnar wrote:
> * Hitoshi Mitake<mitake@xxxxxxxxxxxxxxxxxxxxx>  wrote:
>
> > On 2010å10æ31æ 04:23, Ingo Molnar wrote:
> > > * Hitoshi Mitake<mitake@xxxxxxxxxxxxxxxxxxxxx>   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?

Outputting both result of prefaulted and non prefaulted will be useful,
but this might be not good for using from scripts.
So I'll implement --prefault option first. If there is request
for outputting both, I'll consider to modify default output.

# Please wait about the result of Miao Xie's patch,
# benchmarking memcpy() of unaligned memory area is
# a little difficult

Thanks,
	Hitoshi
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