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<p class=MsoNormal>I’m running x264 on a dual quad core Xeon 3 GHz (E5472)
machine running 64-bit Ubuntu. I’m running the following version of x264,
with no patches, compiled for x86-64:<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>$ x264 --version<o:p></o:p></p>
<p class=MsoNormal>x264 0.65.1072 f586ba5<o:p></o:p></p>
<p class=MsoNormal>built on Jan 6 2009, gcc: 4.3.2<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>I’ve yet to find settings for x264 which keep all the
cores busy on a 720x576 input stream. The best I’ve done is about 60-70%
utilization.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Here are some representative command lines. For actual
encoding I use higher quality settings, but this is a simple example which
shows the effect. I have a “real” example below, <o:p></o:p></p>
<p class=MsoNormal>x264 fifo.y4m -o output.264 --crf 10 --threads auto &<o:p></o:p></p>
<p class=MsoNormal>ffmpeg -i input.mpg -f yuv4mpegpipe - > fifo.y4m<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>I’ve confirmed that I’m not bottlenecked on
decoding the mpeg to yuv4mpeg; that runs about about 500 fps when I have cat
dumping the output of the fifo to /dev/null, and is only taking about 20% of
one core when feeding x264.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>I’ve experimented with setting -threads manually higher
than the 12 that --threads auto selects, but regardless I’m only seeing
400-500% utilization (in top’s 100%-per-core lingo) from x264.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Is it expected that x264 be able to take full advantage of 8
cores, or should I not expect it to scale so far? For this application it is
sometimes but not always possible to batch jobs, so I’m wondering if
there are settings which will make better use of processor resources during a
single run. I found a thread from last year on x264-devel called “x264
and 8 cores”, but it’s not that I’m seeing drastic slowdowns
from a large number of cores, just that I’m not seeing as much speedup as
I’d hoped for.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Here’s an example of my “real” settings. A
fair bit of this is dictated by requirements of a particular hardware decoder I’m
targeting, and I’m running this with patches, as you can see by the
--nal-hrd, but I’ve confirmed my observations with a vanilla build, as
shown above.<o:p></o:p></p>
<p class=MsoNormal>-I 120 --aud --level 3 --vbv-bufsize 8000 --vbv-maxrate
10000 --ref 5 --nal-hrd --trellis 2 --psy-rd 1.0:1.0 --bframes 5 --b-adapt 2
--weightb --direct auto --partitions all --mixed-refs --subme 9 --me umh -B
2400 --pass {1,2}<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>--<o:p></o:p></p>
<p class=MsoNormal>Phil Rutschman<o:p></o:p></p>
<p class=MsoNormal>Senior Software Engineer<o:p></o:p></p>
<p class=MsoNormal>MOD Systems<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
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