[x264-devel] Scalability

[Christian Bienia]

Hi Alex,

> Since the removal of slices has caused so much apparent upset, let me
> just say a word as to the benefits - yes, really ;)   The old threading
> maxed out at roughly 2x the speed of a single-threaded version with
> *any* number of processors and threads (i.e. running with 32 threads on
> 4 processors gave a speedup of 2x; 8 threads on 2 processors was about
> 1.6x).  The new version scales perfectly with number of processors up to
> very large numbers (I don't know the upper limit yet, but certainly >8
> processors).  In fact, it scales sightly better than linearly: the speed
> with 4 processors is ~4.15-4.2x.  Old threading caused substantially
> more bitrate to be used for the same quality; new threading doesn't
> (depending on your settings).  So for most people who really care about
> speed and not so much about the error resilience that slices provide,
> this is a big win.

I just ran x264 on a 128-way ccNUMA, and I think some people here would
also be interested in the results:

#Threads	1	2	4	8	16	32	64
Time/[s]   2280.48 1265.37  661.75  344.77    200.25   201.85  200.97
Speedup            1       1.8     3.45    6.61     11.39     11.3   
11.35

The new threading code is indeed better than the old one, but x264 still
has problems scaling beyond 8 CPUs. Are there any known reasons for
that?

- Chris

-- 
This is the x264-devel mailing-list
To unsubscribe, go to: http://developers.videolan.org/lists.html