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

    * 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?)

    > 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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