[FFmpeg-devel] [RFC] DXVA2 decoding and FFmpeg

[Gwenole Beauchesne]

Hi,

2015-06-16 10:35 GMT+02:00 Stefano Sabatini <stefasab at gmail.com>:
> On date Tuesday 2015-06-16 10:20:31 +0200, wm4 encoded:
>> On Mon, 15 Jun 2015 17:55:35 +0200
>> Stefano Sabatini <stefasab at gmail.com> wrote:
>>
>> > On date Monday 2015-06-15 11:56:13 +0200, Stefano Sabatini encoded:
>> > [...]
>> > > From 3a75ef1e86360cd6f30b8e550307404d0d1c1dba Mon Sep 17 00:00:00 2001
>> > > From: Stefano Sabatini <stefasab at gmail.com>
>> > > Date: Mon, 15 Jun 2015 11:02:50 +0200
>> > > Subject: [PATCH] lavu/mem: add av_memcpynt() function with x86 optimizations
>> > >
>> > > Assembly based on code from vlc dxva2.c, commit 62107e56 by Laurent Aimar
>> > > <fenrir at videolan.org>.
>> > >
>> > > TODO: bump minor, update APIchanges
>> > > ---
>> > >  libavutil/mem.c          |  9 +++++
>> > >  libavutil/mem.h          | 14 ++++++++
>> > >  libavutil/mem_internal.h | 26 +++++++++++++++
>> > >  libavutil/x86/Makefile   |  1 +
>> > >  libavutil/x86/mem.c      | 85 ++++++++++++++++++++++++++++++++++++++++++++++++
>> > >  5 files changed, 135 insertions(+)
>> > >  create mode 100644 libavutil/mem_internal.h
>> > >  create mode 100644 libavutil/x86/mem.c
>> > >
>> > > diff --git a/libavutil/mem.c b/libavutil/mem.c
>> > > index da291fb..0e1eb01 100644
>> > > --- a/libavutil/mem.c
>> > > +++ b/libavutil/mem.c
>> > > @@ -42,6 +42,7 @@
>> > >  #include "dynarray.h"
>> > >  #include "intreadwrite.h"
>> > >  #include "mem.h"
>> > > +#include "mem_internal.h"
>> > >
>> > >  #ifdef MALLOC_PREFIX
>> > >
>> > > @@ -515,3 +516,11 @@ void av_fast_malloc(void *ptr, unsigned int *size, size_t min_size)
>> > >      ff_fast_malloc(ptr, size, min_size, 0);
>> > >  }
>> > >
>> > > +void av_memcpynt(void *dst, const void *src, size_t size, int cpu_flags)
>> > > +{
>> > > +#if ARCH_X86
>> > > +    ff_memcpynt_x86(dst, src, size, cpu_flags);
>> > > +#else
>> > > +    memcpy(dst, src, size, cpu_flags);
>> > > +#endif
>> > > +}
>> >
>> > Alternatively, what about something like:
>> >
>> > av_memcpynt_fn av_memcpynt_get_fn(void);
>> >
>> > modeled after av_pixelutils_get_sad_fn()? This would skip the need for
>> > a wrapper calling the right function.
>>
>
>> I don't see much value in this, unless determining the right function
>> causes too much overhead.
>
> I see two advantages, 1. no branch and function call when the function
> is called, 2. the cpu_flags must not be passed around, so it's somehow
> safer.

Interesting approach. You probably could also use something similar to
sws context you build up based on surface size, and other
characteristics (flags)?

Regards,
-- 
Gwenole Beauchesne
Intel Corporation SAS / 2 rue de Paris, 92196 Meudon Cedex, France
Registration Number (RCS): Nanterre B 302 456 199