[FFmpeg-devel] [PATCH 13/39] lavc/ffv1: drop redundant PlaneContext.quant_table

Paul B Mahol onemda at gmail.com
Thu Jul 18 18:47:06 EEST 2024


On Thu, Jul 18, 2024 at 5:43 PM Anton Khirnov <anton at khirnov.net> wrote:

> Quoting Paul B Mahol (2024-07-18 17:31:50)
> > On Thu, Jul 18, 2024 at 10:20 AM Anton Khirnov <anton at khirnov.net>
> wrote:
> >
> > > Quoting Michael Niedermayer (2024-07-18 00:32:38)
> > > > the data for each decoder task should be together and not scattered
> > > around
> > > > more than needed, reducing cache efficiency
> > > >
> > > > putting all this extra code in the inner per pixel loop is not ok
> > > > especially not for the sake of avoiding a memcpy of a few hundread
> bytes
> > > multiple levels of loops outside
> > >
> > > A nice theory, but in practice this patchset makes single-threaded
> > > decoding about 4% faster overall, on a 1920x1080 10bit sample. That's
> > > just the ffv1 parts (up to patch 28), full set also improves frame
> > > threading performance as follows:
> > > threads         improvement
> > > ---------------------------
> > > 2                  52% (yes really)
> > >
> >
> > What?
>
> Current code is effectively serial with 2 threads.
>

Explains why FFv1 implementation is so slow.


>
> --
> Anton Khirnov
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