Re: [mpeg2-dev] [RFC] [PATCH] ARM Advanced SIMD motion compensation

[Måns R. <ma...@ma...>]

Rémi Denis-Courmont <re...@vi...> writes:

> On Tue, 15 Sep 2009 22:18:22 +0100, Måns Rullgård <ma...@ma...> wrote:
>>> Attached is an intial patch against libmpeg2 trunk to use NEON for
>>> motion compensation. This is preliminary. There are a bunch of known
>>> CPU stalls. Those could probably be fixed using plain assembly and
>>> interleaving subsequent loads. Also, iDCT is not optimized.
>> 
>> Why don't you steal the functions from FFmpeg instead?  They are much
>> better optimised than this patch.
>
> FFmpeg-based MPEG2 decoding was so slow on the target, that I did not even
> consider the possibility that it might have been optimized. For whatever
> reason, it is (eye-)noticeably slower than current libmpeg2 with the
> non-SIMD ARM optimizations. Why is this so? I do not know. There could be
> something wrong with VLC, but then again the FFmpeg h.264 decoding is
> accelerated fine. Or it could be a build problem, or it could be that I did
> not test properly, or it could be a FFmpeg problem in other part.

I have compared FFmpeg against libmpeg2 myself, and FFmpeg on ARMv7 is
about 1.5x faster than libmpeg2.  If your experience with VLC is to
the contrary, there must be a problem in VLC.

-- 
Måns Rullgård
ma...@ma...