Hi, Sorry for the late reply, busy oncall week. Thanks for your responses. I have looked at the code for cpuflags and what you suggested makes sense. I just have a question about naming. EXTERNAL_AVX2_FAST is already used in many places - it checks whether the flag AV_CPU_FLAG_AVXSLOW is set so I can't use this as it would change the meaning of it. Could I define a flag like for AV_CPU_FLAG_CMOV? AV_CPU_FLAG_FAST_GATHER or similar? Or could you please suggest a better solution.
Thanks On Mon, Jun 14, 2021 at 2:17 PM James Almer <jamr...@gmail.com> wrote: > On 6/14/2021 8:53 AM, Ronald S. Bultje wrote: > > Hi Alan, > > > > On Mon, Jun 14, 2021 at 7:20 AM Alan Kelly < > > alankelly-at-google....@ffmpeg.org> wrote: > > > >> Broadwell and later have fast gather instructions. > >> --- > >> This is so that the avx2 version of ff_hscale8to15X which uses gather > >> instructions is only selected on machines where it will actually be > >> faster. > >> > > > > We've in the past typically done this with a bit in the cpuflags return > > value. Can this be added there instead of being its own function? > > > > Also, what is the cycle count of ssse3/avx2 implementation for this > > specific function on Haswell? It would be good to note that in the > > respective patch so that we understand why the check was added. > > Between 9 and 12 on Haswell, 5 to 7 on Broadwell, and about 2 to 5 on > Skylake and newer, acording to Agner's pdf if i'm reading it right. It's > also slow on AMD before Zen 3. > > And yes, this should if anything be a new cpu flag and not a new function. > _______________________________________________ > ffmpeg-devel mailing list > ffmpeg-devel@ffmpeg.org > https://ffmpeg.org/mailman/listinfo/ffmpeg-devel > > To unsubscribe, visit link above, or email > ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe". > _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".
