[FFmpeg-devel] Memcpy Operation Duration

[Ali KIZIL]

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.)
>>
>> Kind Regards,
>> Ali KIZIL
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>> ffmpeg-devel at ffmpeg.org
>> http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
>>
>
> 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.
>
>
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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.

Kind Regards,