[FFmpeg-devel] Anybody has a Core 2? [PATCH] Small SSSE3 optimization

[Loren Merritt]

On Sun, 13 May 2007, Zuxy Meng wrote:
> 2007/5/9, Loren Merritt <lorenm at u.washington.edu>:
>> 
>> You'd get even more speedup by also using SSE2/xmmregs. And both additions
>> would be better written as macros, no need for code duplication.
>
> I saw your recent contribution in svn HEAD. And most interesting to me
> is that in 'svn log' you gave exact cycles of different routines on
> different CPUs. How did u get that? Are u using a simulator or you
> simply measure using RDTSC?

rdtsc, as per ffmpeg's START_TIMER/STOP_TIMER macros. And then subtract 
the time taken by the empty timer, which can be rather large on some 
cpus.
For some functions the time is constant. For others (e.g. with random 
memory access) it can vary, but is still perfectly reproducible if I run 
the same encode twice.

--Loren Merritt