[alsa-devel] [RFC] disabling ALSA period interrupts

pl bossart bossart.nospam at gmail.com
Fri Apr 30 15:44:24 CEST 2010

Hi Clemens,

>> When PulseAudio is used and all PCM is routed through PulseAudio
>> (Fedora, Meego, etc), the notion of ALSA periods isn't very useful.
>> So why not disable them entirely to reduce the number of wakeups? ...
>> There are probably some cases where you don't want this type of
>> behavior (broken hardware, legacy code with multiple-buffering,
>> disabled timer in PulseAudio),
> It's interesting that all ALSA applications except PA are "legacy".  :)

Ha. Nice slip. I didn't mean legacy was bad... It's perfectly ok to
use multiple buffers and interrupts in a variety of apps.

>> so I think it would make sense to request the disabling of interrupts
>> when hw_params are set, since this is also the time when period sizes
>> are set.
> Yes.  For compatibility with the existing ALSA API, this needs to be
> a flag that is not enabled by default.

Agreed. This shouldn't even be mandatory since this option might not
be possible in all platforms.

>> I am aware that some changes would be needed in pcm_lib.c, where all
>> the error checks are done.
> Plus all the API changes in the ALSA kernel framework, the ALSA kernel/
> userspace interface, and the alsa-lib interface.

I am not following this point. If you add a simple flag to an existing
interface, why would we need to change the kernel/userspace inferface?
This change should be possible in a backwards compatible manner as an
additional option provided to the application developer.

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