[alsa-devel] pulseaudio eats 19% CPU power in Fedora 12

Raymond Yau superquad.vortex2 at gmail.com
Mon Apr 19 10:34:05 CEST 2010

2010/4/19 Lennart Poettering <mznyfn at 0pointer.de>

> On Wed, 14.04.10 15:56, Wu Fengguang (fengguang.wu at intel.com) wrote:
> > Hi Lennart,
> >
> > We found that pulseaudio eats CPU ~19% CPU time, a little more than
> > mplayer when playing video. This is horrible for laptop batteries.
> This is not a particularly useful report.
> You know, this can have so many different reasons, the only thing I can
> really say, is that you can rest assured that it is not supposed to eat
> that much in normal use.
> The CPU usage of PA is primarily dependant of the latency requested by
> the clients. Low latency means high CPU load. Lower latency means higher
> CPU load. Try "pacmd list-sink-inputs" to figure out the latency the
> various applications requested.
> Then there can be driver problems, where the timing information is not
> entirely correct that ALSA passes on to, with the result that we get
> dropouts where we shouldn't, with the results that we shorten our sleep
> times, with the final effect that the CPU usage goes up.
> Of course, if PA is used resampling and suchlike is moved from the
> clients into the sound server and hence will be added to its CPU
> usage. And PA uses a better resampler by default than ALSA traditionally
> did, hence the CPU use will be a bit higher than plain ALSA.
> And then of course, the CPU usage depends on the CPU used. Is this some
> embedded hardware?
> In summary: if you want to know what is going on, you need a suitable
> tool, like a profiler and do the dirty work to figure out what is going
> on. Just saying "19%" is not helpful to figure out what is going on.
> On my machine here it uses 3% CPU while playing.
> > Can we make it just work -- in green CPU mode?
> Yes, sure. If you use "pacat" you can play audio with almost zero CPU
> usage, because it is one of the few clients that actually asks for
> sensible latency (2s), which allows us to minimize the wakeup intervals
> to less than a second.
> > I can find many users
> > complaining about this, and it seems like some fix is available in
> > this link:
> > https://bugs.launchpad.net/ubuntu/+source/pulseaudio/+bug/207135
> Fix? Where?
> Lennart
AFAIK , the CPU usage increase with the number of applications connected to
PA server .

If I run 4 instances of mplayer on Fedora 10 , the CPU usage will increase
from 3% to 12%

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