On Tue, Oct 25, 2016 at 12:00:01AM +0200, Hendrik Leppkes wrote: > On Mon, Oct 24, 2016 at 10:31 PM, Ronald S. Bultje <rsbul...@gmail.com> wrote: > > Hi, > > > > On Mon, Oct 24, 2016 at 4:26 PM, Henrik Gramner <hen...@gramner.com> wrote: > > > >> On Mon, Oct 24, 2016 at 9:59 PM, Ronald S. Bultje <rsbul...@gmail.com> > >> wrote: > >> > Good idea to reference Hendrik Gramner here, who keeps insisting we get > >> rid > >> > of all MMX code in ffmpeg (at least as an option) for future Intel CPUs > >> in > >> > which MMX will be deprecated. > >> > >> Replacing MMX with SSE2 is indeed the most "proper" fix in my opinion, > >> but it's a fair amount of work and not done in an evening. > >> > >> The fact that a lot of assembly lacks unit tests is certainly not > >> helping in that regard. > >> > >> Some MMX instructions are slower than the equivalent SSE2 code on > >> Skylake. Intel hasn't officially commented on (as far as I know at > >> least) if we should expect this trend to continue, but they certainly > >> seem to treat MMX as legacy. > >> > >> I doubt they would completely remove support for it though, backwards > >> compatibility is a big selling-point for x86. > > > > > > Well, it gives us another way of fixing this issue (on x86-64 only): have > > sse2 implementations for all code that has a mmx (register) path right now. > > > > I don't think the argument for pre-sse2 CPUs is that strong on 32-bit > systems, either.
SSE2 was initially not faster than MMX as CPUs implemented it as 2 MMX operations internally not having a full width SIMD unit for SSE* so there would be a performace loss on some x86-32 CPUs if MMX was replaced by "half-width SSE2" there [...] -- Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB Everything should be made as simple as possible, but not simpler. -- Albert Einstein
signature.asc
Description: Digital signature
_______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
