[x264-devel] Hyperthreading

[Jason Garrett-Glaser]

On Thu, Aug 26, 2010 at 11:28 AM, Dennis Munsie <dmunsie at gmail.com> wrote:
> Hi --
> Does x264 have any support for detecting that it's running on a
> Hyperthreaded enabled CPU and to only spawn threads for each real CPU? I've
> noticed that on our quad core i7s, we've seen a total of 9 threads when
> doing slice based threading (for low-latency support) when encoding a 720p
> clip.  Since the load on the machine appears to be 50% overall and it
> doesn't get slower when we turn off HT, it appears those extra threads are
> unable to get the resources to actually run in parallel with the 4 other
> threads.
> I am using x264 as a library in my own program -- so it may be that I've
> just missed a configuration option that I should've set.
> Thanks!
> dennis

Our testing strongly suggests that the number of virtual cores is
optimal when using sliced threads, even when HT is on:

http://saintdevelopment.com/benchmarks/bfs-vs-cfs/720p_i7/2.6.32-720p-0lat-vf-nob.png

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