[FFmpeg-devel] [flamefest-start] A little something on MMX/SSE intrinsics
Fri Feb 29 13:35:01 CET 2008
On Thu, Feb 28, 2008 at 11:11:07PM +0100, Luca Barbato wrote:
> Mike Melanson wrote:
> > Luca Barbato wrote:
> >> So, what about having a SoC on this kind of stuff?
> > SoC what? Project? Or qualification task? What would be the goal? And
> > who would be the mentor.
> Qualification :
> - convert from intrisics to asm or from asm to intrinsics 4-5
> nontrivial functions.
Honestly i dont think converting asm to intrisics is such a good idea.
This is like rewriting ffmpeg is java ...
Also the student has to do intrinsics->asm properly (assigning registers
sanely, avoid unneeded load/stores shedule instructions half sane, ...).
> - benchmark the results.
Qualification should _require_ the new code to be faster than the intrinsics.
The reason being a student failing to write asm code which beats gcc is not
someone i want optimizing ffmpeg.
Also anyone can within 5 minutes just run gcc -S over the code and just change
this to asm (which would result in identical speed on the target cpu) so someone
submitting slower code really fails IMO.
> SoC :
> - split x86 from x86_64, rewrite for speed for x86_64,
Iam not in favor of brute force spliting, first there has to be some
plan/idea for each individual asm(), that is "we could avoid these 3
load/stores if we had 3 more registers" Also for splited code to be accepted
it must be impossible to have a equally fast and reasonable clean combined
> asm AND
Iam not in favor of this.
> benchmark the results.
benchmark on what? one cpu? several? do we have shell accounts for idle
machines with these cpus?
> - improve the simd coverage for $arch
Too vague IMHO, we should have some list of functions to optimize at least
as starpoint, the student could always optimize other things too ...
Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
Good people do not need laws to tell them to act responsibly, while bad
people will find a way around the laws. -- Plato
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