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

[lance.lmwang at gmail.com]

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).


> 
> i think the commit message should be more verbose describing what the
> problem is that this is fixing
> 
> thx
> 
> [...]
> -- 
> Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
> 
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-- 
Thanks,
Limin Wang