On Thu, May 14, 2015 at 2:52 PM, Stefano Sabatini <stefa...@gmail.com> wrote: > On date Thursday 2015-05-14 13:01:51 +0200, Stefano Sabatini encoded: >> On date Tuesday 2015-05-12 15:54:17 +0200, Hendrik Leppkes encoded: > [...] >> > One limitation is as the manual said, it needs to be copied from the >> > GPU to system memory. ffmpeg_dxva2.c does not implement a optimized >> > copy function for this, it uses plain old memcpy. >> > Intel introduced a new instruction for this in SSE4, MOVNTDQA, which >> > is optimized for copying from USWC memory (Uncacheable Speculative >> > Write Combining) to system memory. Using this may help speed up the >> > process significantly, and VLC probably uses it. >> >> Now the question is, how would be possible to optimize GPU to CPU copy >> to get an overall performance gain? At least VLC seems able to get >> better performances when using HW decoding, but I'm not sure it is >> copying decoded data back to the CPU (indeed it may perform direct >> rendering). > > Self-reply: > commit 62107e563f979c638f9a5f58cdfd5639d9c63ac7 > Author: Laurent Aimar <fen...@videolan.org> > Date: Tue Nov 17 01:09:43 2009 +0100 > > Improved performance when copying video surface in dxva2. > > That is, VLC is using optimized GPU->CPU copy when the relevant SSE2 > instructions are available.
Actually the real proper instructions are SSE4.1, using SSE2 would only be a small advantage over memcpy. - Hendrik _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
