[x264-devel] x264 & slices

[ollo.diab at gmx.de]

Hi Tuukka,

I tried recent x264 enabled mencoder to trancode a HDTV mpeg2 file to H.264
avi on a Quad Opteron system running RedHat Enterprise 3 64bit. x264 got
build with pthread enabled.

Now if I run mencoder with default x264 encoder settings and add the
threads=1 parameter, then I get about 5fps, fine. But the odd thing is, all
4 CPUs are busy at around 25%. Then I tried threads=2, the rate got to 7fps
and all 4 CPUs are running at 35% load. With threads=3 the rate goes to 8fps
and with threads=4 goes to 9fps while all CPUs run at 50% load.

Somehow I was under the impression the thread parameter more or less defines
how many CPUs get used. So I expected to see a load of 100% on a single CPU
with threads=1 and on 2 CPUs with threads=2 and so on.

What is going on? Where is the bottleneck to use multiple CPUs for encoding
at full load (and thus high fps rate)?

Thanks & regards,   Thomas

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