[Spice-devel] [spice] streaming: Use the optimal number of threads for VP8 encoding

[Frediano Ziglio]

> 
> Hi,
> 
> On Mon, Oct 31, 2016 at 08:49:23PM +0100, Francois Gouget wrote:
> > We run the VP8 encoder in real time mode so it uses only the minimum
> > amount of time needed to encode each frame. However by default it
> > only uses one thread so that for large/complex frames it may run at
> > less than the source fps. Besides resulting in dropped frames this
> > blocks the main server thread for most of the time.
> > So this patch configures the VP8 encoder to use all the CPU's physical
> > core, resulting in less wall clock time spent in encode_frame().
> > 
> > Signed-off-by: Francois Gouget <fgouget at codeweavers.com>
> > ---
> > 
> > I am resubmitting this patch because I think the reasons for not
> > applying it last time were wrong. See:
> > https://lists.freedesktop.org/archives/spice-devel/2016-March/027026.html
> > 
> > Here is an illustration of the impact of threading for the
> > big_buck_bunny_1080p_h264.mov video:
> > 
> > http://fgouget.free.fr/tmp/Spice-vp8-threads.png
> > http://fgouget.free.fr/tmp/Spice-vp8-threads.xls
> > 
> > The graph shows the time spent in encode_frame() (taken from the
> > standard traces) when vp8enc uses 1, 2 or 4 threads.
> 
> Well, I did not say that using more threads was not useful, I was only
> worried that using all CPUs could not be so good (eg multiple VMs
> encoding at the same time), especially as I think you mentioned that
> trying to use too many threads was causing rendering issues?
> 

I agree with both... I think the solution is an option to enable/disable
and personally I would prefer to use less thread by default.

> > I'll also note that the h264 encoder automatically uses multiple
> > threads already so this patch only brings vp8enc in line with it.
> 
> After a quick look at x264, it seems to be using more threads than
> physiical CPUs. Is it ok too with vp8enc? I'd really like that we don't
> have that code invoking egrep as a fallback, ie no g_get_num_processors,
> no _SC_NPROCESSORS_ONLN, tough luck? (the latter is available on el6).
> 
> Christophe
> 

I think we can assume, if system has not these options has only one
core...

Frediano