Re: [FFmpeg-devel] [PATCH v3] lavc/libvpx: remove thread limit

["mypopy@gmail.com" <mypopy@gmail.com>]

On Thu, Jan 5, 2023 at 6:42 PM Dmitrii Ovchinnikov
<ovchinnikov.dmitrii@gmail.com> wrote:
>
> From: Dmitrii Ovchinnikov <ovchinnikov.dmitrii@gmail.com>
>
> This change improves the performance and multicore
>  scalability of the vp9 codec for streaming single-pass encoded videos. The
>  current thread limit for ffmpeg codecs is 16 (MAX_AUTO_THREADS in
>  pthread_internal.h) due to a limitation in H.264 codec that prevents more
>  than 16 threads being used.
>
> Increasing the thread limit to 64 for vp9 improves
> the performance for encoding 4K raw videos for streaming by up to 47%
> compared to 16 threads, and from 20-30% for 32 threads, with the same quality
> as measured by the VMAF score.
>
> Did not need to add a check for limit in libvpx as it is already present
> in libvpx/vp9/vp9_cx_iface.c:
>   RANGE_CHECK_HI(cfg, g_threads, 64);
> As demonstrated by following message when -threads is set to anything more than 64
> [libvpx-vp9 @ 0x30ed380]   Additional information: g_threads out of range [..64]
>
> ---
>  libavcodec/libvpxdec.c | 2 +-
>  libavcodec/libvpxenc.c | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/libavcodec/libvpxdec.c b/libavcodec/libvpxdec.c
> index 9cd2c56caf..19407092d0 100644
> --- a/libavcodec/libvpxdec.c
> +++ b/libavcodec/libvpxdec.c
> @@ -88,7 +88,7 @@ static av_cold int vpx_init(AVCodecContext *avctx,
>                              const struct vpx_codec_iface *iface)
>  {
>      struct vpx_codec_dec_cfg deccfg = {
> -        .threads = FFMIN(avctx->thread_count ? avctx->thread_count : av_cpu_count(), 16)
> +        .threads = avctx->thread_count ? avctx->thread_count : av_cpu_count()
>      };
>
>      av_log(avctx, AV_LOG_INFO, "%s\n", vpx_codec_version_str());
> diff --git a/libavcodec/libvpxenc.c b/libavcodec/libvpxenc.c
> index 9aa5510c28..0627e13973 100644
> --- a/libavcodec/libvpxenc.c
> +++ b/libavcodec/libvpxenc.c
> @@ -942,7 +942,7 @@ static av_cold int vpx_init(AVCodecContext *avctx,
>      enccfg.g_timebase.num = avctx->time_base.num;
>      enccfg.g_timebase.den = avctx->time_base.den;
>      enccfg.g_threads      =
> -        FFMIN(avctx->thread_count ? avctx->thread_count : av_cpu_count(), 16);
> +        avctx->thread_count ? avctx->thread_count : av_cpu_count();
>      enccfg.g_lag_in_frames= ctx->lag_in_frames;
>
Do you check the change with the old version libvpx?  as I know, older
versions libvpx setting the number of threads higher than 16 will
cause a crash, so I think at least a version check needs to be added

>      if (avctx->flags & AV_CODEC_FLAG_PASS1)
> --
> 2.38.1.windows.1
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