[pulseaudio-discuss] 61ms delay in pa_simple_write()

H. Peter Anvin h.peter.anvin at intel.com
Fri Sep 24 12:05:34 PDT 2010

On 09/24/2010 09:11 AM, pl bossart wrote:
>> For normal alsa playback, their typical values are 1024.  Pulseaudio
>> sets them to large values and maybe is not entirely depending on the
>> poll. It may be setting some timer to wake up itself when the DMA
>> buffer runs low on data.
>> Anyway the pulseaudio's large buffer scheme makes possible the 61ms
>> pa_simple_write(). Qemu is not expecting such a large latency. Its
>> QEMU_PA_SAMPLES defaults to 1024, which can only hold up to
>> 1024/48=21ms samples. So the 61ms delay will obviously overflow the
>> "data push" based USB audio model..
> The default PulseAudio configuration is 4 periods of 25 ms each. You
> can reduce this if you want by changing the relevant fields in
> /usr/etc/daemon.conf
> -Pierre

Note, I haven't looked at the delays in pa_simple_write, but I
definitely see audio stops on the order of seconds, which could
realistically only be caused by either starvation or entire buffers
getting thrown out.


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