[FFmpeg-devel] [PATCH 2/2] avutil/slicethread: Add a maximum constraint of 16 slice threads

[lance.lmwang at gmail.com]

On Sat, Nov 06, 2021 at 08:42:38AM +0100, Hendrik Leppkes wrote:
> On Sat, Nov 6, 2021 at 6:26 AM <lance.lmwang at gmail.com> wrote:
> >
> > On Fri, Nov 05, 2021 at 10:00:41PM +0100, Michael Niedermayer wrote:
> > > On Fri, Nov 05, 2021 at 08:32:16PM +0800, lance.lmwang at gmail.com wrote:
> > > > From: Limin Wang <lance.lmwang at gmail.com>
> > > >
> > > > Signed-off-by: Limin Wang <lance.lmwang at gmail.com>
> > > > ---
> > > >  libavutil/slicethread.c | 2 +-
> > > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > >
> > > > diff --git a/libavutil/slicethread.c b/libavutil/slicethread.c
> > > > index 867ce32..7b3a106 100644
> > > > --- a/libavutil/slicethread.c
> > > > +++ b/libavutil/slicethread.c
> > > > @@ -104,7 +104,7 @@ int avpriv_slicethread_create(AVSliceThread **pctx, void *priv,
> > > >      if (!nb_threads) {
> > > >          int nb_cpus = av_cpu_count();
> > > >          if (nb_cpus > 1)
> > > > -            nb_threads = nb_cpus + 1;
> > > > +            nb_threads = FFMIN(nb_cpus + 1, 16);
> > >
> > > why should the threads be limited ?
> > > why should they be limited at 16 for everyone ?
> > > one mighht be a 2 core cpu one might have 200 cores
> >
> > When using movie filter, it use ff_filter_get_nb_threads(ctx), but we can't force the thread
> > number by option, so it's auto thread mode. When testing one a 4 core cpu(about 200 cores),
> > the auto thread mode will use all cores for video decode, it'll drop the performance very much.
> > If most of user prefer to use all cores, I'll try to limit the number in movie filter only.
> >
> > For a 4 socket numa system, I don't think it's preferable configure to use all cpu cores
> > if it's auto thread(nb_threads = 0).
> >
> >
> 
> The answer to that issue should be to make it configurable, and not
> just introduce a hard limit in a utility function in avutil.

OK, I'll add a thread option for src_movie filter to make the decode thread configurable.

> 
> - Hendrik
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-- 
Thanks,
Limin Wang