[FFmpeg-devel] Memcpy Operation Duration

[Ali KIZIL]

On Oct 18, 2016 11:08 PM, "Ronald S. Bultje" <rsbultje at gmail.com> wrote:
>
> Hi Ali,
>
> On Tue, Oct 18, 2016 at 3:57 PM, Ali KIZIL <alikizil at gmail.com> wrote:
>
> > 2016-10-18 22:44 GMT+03:00 Sven C. Dack <sven.c.dack at sky.com>:
> >
> > > On 18/10/16 20:26, Ali KIZIL wrote:
> > >
> > >> Hi Everyone,
> > >>
> > >> Today, I was analyzing memcpy duration in FFmpeg. I noticed that it
is
> > >> taking longer time compared to an optimized SSE, SSE2, MMX, MMX2,
AVX or
> > >> AVX2 based memcpy operation.
> > >>
> > >> I tried march=corei7-avx2 compiled FFmpeg version, it does not change
> > the
> > >> duration of memcpy operation.
> > >> I also folowed https://trac.ffmpeg.org/wiki/C
> > >> ompilationGuide#PerformanceTips
> > >> .Same result. In addition, I tried gcc 6.2 if gcc if gcc is not
> > selecting
> > >> the correct flag. Same result again.
> > >>
> > >> This memcpy operations effect the fps decoding (and probably
encoding)
> > >> rates.
> > >>
> > >> In a case that uyvy422 to p010 3840x2160 unscaled convertion in
> > rawvideo,
> > >> fps rate increased from 44 fps to 52 fps on a Xeon E5 2630 v4.
> > >>
> > >> Do I miss anything when compiling FFmpeg for AVX2 or other flag
> > optimised,
> > >> or there need a fix in FFmpeg to direct some (or all)  memcpy
operations
> > >> to
> > >> a inherited memcpy operation which can decide flag for optimisation ?
> > >> Or there is no such need and I am on a wrong path ?
> > >>
> > >> (As a side note, FFmpeg works performance on i7 Extreme cores
compared
> > to
> > >> Xeon v4 processors.)
> > >
> > > Could be it's gcc's built-in version. It's been said that libc is
> > > occasionally better at it than gcc's built-in version.
> > >
> > > Use -fno-builtin-memcpy and see what difference it makes.
> >
>
> >
> I see, tomorrow morning I will give it a try.
> > Thank you for the good idea. If it increase performance, maybe it will
be a
> > good idea to make a configure option.
>
>
> configure has --extra-cflags=.. and --extra-ldflags=.. options to add
> custom CC CLI arguments.
>
> Ronald
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Hi Ronald,

Yes, I used extra flags to give march=native or march=corei7-avx2.
Tomorrow, I will try -fno-builtin-memcpy option with extra-cflag. I will
update the topic.

Thank you,