On Wed, 2016-07-06 at 09:07 +0200, Hendrik Leppkes wrote: > On Wed, Jul 6, 2016 at 4:37 AM, Dan Parrot <dan.par...@mail.com> wrote: > > Finish providing SIMD versions for POWER8 VSX of functions in > > libswscale/input.c That should allow trac ticket #5570 to be closed. > > The speedups obtained for the functions are: > > > > abgrToA_c 1.19 > > bgr24ToUV_c 1.23 > > bgr24ToUV_half_c 1.37 > > bgr24ToY_c_vsx 1.43 > > nv12ToUV_c 1.05 > > nv21ToUV_c 1.06 > > planar_rgb_to_uv 1.25 > > planar_rgb_to_y 1.26 > > rgb24ToUV_c 1.11 > > rgb24ToUV_half_c 1.10 > > rgb24ToY_c 0.92 > > rgbaToA_c 0.88 > > uyvyToUV_c 1.05 > > uyvyToY_c 1.15 > > yuy2ToUV_c 1.07 > > yuy2ToY_c 1.17 > > yvy2ToUV_c 1.05 > > SIMD implementations that in the best case improve the speed by 43% > (and in some cases is *slower*) seem barely worth it. One would expect > a proper SIMD implementation to offer 100% or higher increases, at > least thats the general expectation on x86 with SSE/AVX. It sounds like you have either forgotten or never learned a very basic principle of computer architecture. I recommend the text by Patterson and Hennessey. The principle is Amdahl's Law. Before you start throwing numbers around, make sure you understand what was being parallelized.
> So the question here is - is thats VSX being bad, or the intrinsics > being bad? How would the speedup be in proper hand-written ASM? > If hand-written ASM can give us the usual 100-200% improvements we would > expect from SIMD, then this is what should generally be favored. I am not got to write assembly just so you get a nice fuzzy feeling. If that's a deal-breaker, so be it. > Also, one further thought: > From the commit message, it sounds like you might only be doing this > for the bounty in #5570, do you plan to maintain these optimizations > in the future? Unless you are a mind reader, STFU about my motivation in writing code. One other thing: why didn't this come up when the earlier patch was submitted and applied? _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
