optimize for multicore

optimize for multicore

[chronek]

Hello,

 I have Debian testing distro with gcc 4.7.2 running on virtualbox where
assigned 8 cores and have some questions regarding gcc optimize flags. I
want run mencoder to filter big resolution video with uspp (that filter
calling snow encoder for encode/decode and avarage result (snow from ffmpeg
what is compiling with mencoder)). I use simple flags like -O3 -march=native
-mtune=native -mssse3 -fomit-from-pointer (cause it is virtual host it see
my i7 like core2 with max ssse3 instruction). 
 Is a way to compile for use more than one core/thread without changes in
sources, only just by add optimize flags? What flag would be best for
virtual host and speed up filtering? Is a way to check if it is memory or
cpu problem? (filtering with max quality filter on fullhd source is 1 thread
and 0.23 fps speed)

Mike



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Re: optimize for multicore

[Andrew Haley]

On 01/18/2013 08:13 AM, chronek wrote:

>  I have Debian testing distro with gcc 4.7.2 running on virtualbox where
> assigned 8 cores and have some questions regarding gcc optimize flags. I
> want run mencoder to filter big resolution video with uspp (that filter
> calling snow encoder for encode/decode and avarage result (snow from ffmpeg
> what is compiling with mencoder)). I use simple flags like -O3 -march=native
> -mtune=native -mssse3 -fomit-from-pointer (cause it is virtual host it see
> my i7 like core2 with max ssse3 instruction). 
>  Is a way to compile for use more than one core/thread without changes in
> sources, only just by add optimize flags? What flag would be best for
> virtual host and speed up filtering? Is a way to check if it is memory or
> cpu problem? (filtering with max quality filter on fullhd source is 1 thread
> and 0.23 fps speed)

GCC has auto-vectorization, which helps with some loops, but I doubt
that it'll help you.  http://gcc.gnu.org/projects/tree-ssa/vectorization.html

Video encoding can benefit considerably from multiple cores, but it
really needs the programmer to split the code into separate tasks.

Andrew.