[alsa-devel] ALSA calling pcm_pointer excessively?

[Russell King - ARM Linux]

On Thu, May 10, 2012 at 10:30:44PM +0530, Jassi Brar wrote:
> On Thu, May 10, 2012 at 9:36 PM, Russell King - ARM Linux
> <linux at arm.linux.org.uk> wrote:
> >
> > The question is - what would cause ALSA to hammer away at the buffer
> > like that - checking it every 16 or 8 DMA bytes transferred?  I'm also
> > seeing around 75% system CPU time, which really isn't good.
> >
> > The above was captured while aplay was running, with no apparant audio
> > corruption.
> >
> > Any ideas?
> >
> I believe it's because the pcm's write tries to keep the data in ring
> buffer filled
> upto brim and keeps polling the dma position till it keeps reporting
> some progress.
> 
> I think if you could avoid that behavior if your driver carefully
> keeps negligible
> progresses to itself and report only considerable ones. Basically, core would
> stop polling and wait on queue when two pointer calls return same value i.e no
> progress.

You _could_ but why should drivers work around silly behaviour in the
ALSA core?