[alsa-devel] Timer instability

[Takashi Iwai]

At Sun, 22 Feb 2009 04:14:53 +0100,
Lennart Poettering wrote:
> 
> On Sat, 21.02.09 17:36, Takashi Iwai (tiwai at suse.de) wrote:
> 
> > 
> > At Fri, 20 Feb 2009 21:34:17 +0100,
> > Lennart Poettering wrote:
> > > 
> > > On Fri, 20.02.09 08:26, Takashi Iwai (tiwai at suse.de) wrote:
> > > 
> > > > > Yes, I am. But ignore that part for now. I have now commented the use
> > > > > of that call. Now I certainly get more POLLOUTs as expected, but the
> > > > > real problem stays: after a few minutes _avail() will suddenly jump
> > > > > from next to zero to more then the hwbuf size in less than 1ms without
> > > > > any further inteference and with a buffer size of 350ms! There is
> > > > > something really wrong with the behaviour of _avail().
> > > > > 
> > > > > I can reproduce this only on ens1371 for now.
> > > > 
> > > > The ens1371 driver itself is damn simple.  The pointer callback just
> > > > returns the read value.  So, it implies that it's basically a hardware
> > > > issue.
> > > > 
> > > > Does the patch below have any influence?
> > > 
> > > No. It doesn't appear to have any effect whatsoever. Still, from time
> > > to time the value returned by _avail() is off by once the buffer size,
> > > sometimes upwards, sometimes downwards.
> > > 
> > > Moreover I can now reproduce the same issue on snd-intel8x0, albeit it
> > > takes more than a couple of minutes to make snd_pcm_avail() return
> > > bogus data.
> > > 
> > > Somehow I get the feeling the problem is not so much the inaccuracy of
> > > the pointer the kernel reports but in what alsa-libs does ith it.
> > 
> > Hrm... both cases the pointer calculation is relatively simple,
> > and for "hw" PCM, the avail calculation is also very straightforward.
> > So, my first suspect is about the pointer calculation.  But, of course
> > we should check all possibilities.
> > 
> > Can you give a small testcase?
> 
> Ok, here's a little test case:
> 
> http://git.0pointer.de/?p=pulseaudio.git;a=blob_plain;f=src/tests/alsa-time-test.c

Thanks.  Will check it later.


Takashi