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

Anvin, H Peter h.peter.anvin at intel.com
Fri Sep 24 09:29:26 PDT 2010

What does that mean in terms of maximum latency?  Either way, it sounds like the 21 ms buffering in Qemu is way insufficient if there are those kinds of latencies in PA.

Unfortunately even when I tried it with a 16x larger buffer (and the resulting extended latency) I saw problems.


-----Original Message-----
From: pl bossart [mailto:bossart.nospam at gmail.com] 
Sent: Friday, September 24, 2010 9:12 AM
To: General PulseAudio Discussion
Cc: Lennart Poettering; Anvin, H Peter; malc
Subject: Re: [pulseaudio-discuss] 61ms delay in pa_simple_write()

> 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

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