[alsa-devel] ALSA calling pcm_pointer excessively?

[Jassi Brar]

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.