Lukas Fellechner: >> Gesendet: Montag, 05. September 2022 um 21:58 Uhr >> Von: "Martin Storsjö" <mar...@martin.st> >> An: ffmpeg-devel@ffmpeg.org >> Betreff: Re: [FFmpeg-devel] [PATCH] slicethread: Limit the automatic number >> of threads to 16 >> On Mon, 5 Sep 2022, Martin Storsjö wrote: >> >>> This matches a similar cap on the number of automatic threads >>> in libavcodec/pthread_slice.c. >>> >>> On systems with lots of cores, this does speed things up in >>> general (measurable on the level of the runtime of running >>> "make fate"), and fixes a couple fate failures in 32 bit mode on >>> such machines (where spawning a huge number of threads runs >>> out of address space). >>> --- >> >> On second thought - this observation that it speeds up "make -j$(nproc) >> fate" isn't surprising at all; as long as there are jobs to saturate all >> cores with the make level parallelism anyway, any threading within each >> job just adds extra overhead, nothing more. >> >> // Martin > > Agreed, this observation of massively parallel test runs does not tell > much about real world performance. > There are really two separate issues here: > > 1. Running out of address space in 32-bit processes > > It probably makes sense to limit auto threads to 16, but it should only > be done in 32-bit processes. A 64-bit process should never run out of > address space. We should not cripple high end machines running > 64-bit applications. > > > Sidenotes about "it does not make sense to have more than 16 slices": > > On 8K video, when using 32 threads, each thread will process 256 lines > or about 1MP (> FullHD!). Sure makes sense to me. But even for sw decoding > 4K video, having more than 16 threads on a powerful machine makes sense. > > Intel's next desktop CPUs will have up to 24 physical cores. The > proposed change would limit them to use only 16 cores, even on 64-bit. >
This part is completely wrong: You can always set the number of threads manually. (Btw: 1. 8K is the horizontal resolution; the vertical resolution of it is 4360 (when using 16:9), so every thread processes 135 lines which have as many pixels as 540 lines of FullHD. 2. FullHD has about 2MP.) - Andreas _______________________________________________ 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".
