[alsa-devel] Timer instability

Lennart Poettering mznyfn at 0pointer.de
Fri Feb 20 21:34:17 CET 2009

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.


Lennart Poettering                        Red Hat, Inc.
lennart [at] poettering [dot] net         ICQ# 11060553
http://0pointer.net/lennart/           GnuPG 0x1A015CC4

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