[pulseaudio-discuss] [PATCH] Do not use tsched watermark if tsched is disabled
david.henningsson at canonical.com
Tue Sep 7 23:27:02 PDT 2010
On 2010-09-08 02:52, pl bossart wrote:
>>> So what does this test mean? pavucontrol obviously affects the latency
>>> of the sink due to it's VI meters. This obviously increases the
>>> likelihood of a rewind being triggered.So, with this in mind what
>>> values do you suggest we pick?
>> Pierre, is it your understanding that it is when DMA transfer collides with
>> cpu->RAM transfer that makes the DMA stream to become broken permanently? Or
>> exactly what is it that makes it break?
> The low-latency setting has nothing to do with rewinds.
Indirectly it is - if the rewind margin is greater than the actual
latency there won't be any rewind.
> It's when you
> actually change the volume that you will rewind and remix with the new
> stream volume. You could set a super low latency and rewind exactly
> once when the stream starts.
> There are two issues with the rewind. One is a race condition between
> the DMA and the ring buffer update. If you rewind and update the ring
> buffer, the DMA may actually have already fetched older data.
To fetch the old data is not a problem IMO, that gives us just a ms more
of the old data and we might miss a ms of the new data. That's not
optimal, but not a complete disaster either.
What is the big problem here, is when we get a persistent crackling
(even when everything has straightened out after the rewind!), and if I
understand you correctly, that has something to do with the DMA
controller...? Could you elaborate on what conditions it is that cause
the persistent crackling?
> second is that you could experience underflows if you don't do the
> update fast enough. By enabling logs you should be able to find out if
> there are real underflows.
David Henningsson, Canonical Ltd.
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