[FFmpeg-devel] [PATCH] avcodec/libvpxdec: fix setting auto threads

[James Zern]

On Sat, Oct 27, 2018 at 1:54 PM James Almer <jamrial at gmail.com> wrote:
>
> On 10/27/2018 5:52 PM, James Zern wrote:
> > a thread count of 0 is treated the same as 1, use av_cpu_count() to get
> > the correct thread count when auto threads is requested.
> >
> > this matches the fix in libvpxenc:
> > 27df34bf1f avcodec/libvpxenc: fix setting amount of threads used for encoding
> >
> > Signed-off-by: James Zern <jzern at google.com>
> > ---
> >  libavcodec/libvpxdec.c | 3 +--
> >  1 file changed, 1 insertion(+), 2 deletions(-)
> >
> > diff --git a/libavcodec/libvpxdec.c b/libavcodec/libvpxdec.c
> > index 04f27d3396..5193ac51c3 100644
> > --- a/libavcodec/libvpxdec.c
> > +++ b/libavcodec/libvpxdec.c
> > @@ -47,8 +47,7 @@ static av_cold int vpx_init(AVCodecContext *avctx,
> >  {
> >      VPxContext *ctx = avctx->priv_data;
> >      struct vpx_codec_dec_cfg deccfg = {
> > -        /* token partitions+1 would be a decent choice */
> > -        .threads = FFMIN(avctx->thread_count, 16)
> > +        .threads = avctx->thread_count ? avctx->thread_count : av_cpu_count()
>
> If the limit of 16 threads is correct and unless libvpx clips it on its
> own, then you shouldn't remove the check.
>

If anything it was a limit put in at one stage of vp8 development, the
comment is certainly vp8 specific. vp8/9 both clip in their own ways
[1][2], but looking at it there may have been some changes to the loop
filter that aren't limiting this number. I'll restore it to be safe.
On the libvpxenc side I don't think there was ever a check in the
wrapper, but the library does put a hard cap on the requested threads
(64) and will fail otherwise.

[1] https://chromium.googlesource.com/webm/libvpx/+/v1.7.0/vp8/decoder/threading.c#596
[2] https://chromium.googlesource.com/webm/libvpx/+/v1.7.0/vp9/decoder/vp9_decodeframe.c#1542

> LGTM otherwise.
>
> >      };
> >
> >      av_log(avctx, AV_LOG_INFO, "%s\n", vpx_codec_version_str());
> >
>
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