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

[Liam Girdwood]

On Thu, 2010-04-29 at 17:38 -0500, pl bossart wrote:
> Howdy,
> When PulseAudio is used and all PCM is routed through PulseAudio
> (Fedora, Meego, etc), the notion of ALSA periods isn't very useful.
> PulseAudio uses a timer to refill buffers and the period interrupts
> are not used at all.
> 
> So why not disable them entirely to reduce the number of wakeups? This
> is possible with a number of existing DMA controllers. The simple
> patch attached shows a proof-of-concept on HDAudio, it's been working
> for 5 hours on my Fedora12 laptop without any glitches and powertop
> does show _zero_ wakeups from the HDAudio controller (except on
> startup). I am told by my colleagues working in Windows environments
> that this is what's done on Vista/Windows7 btw. This isn't to say
> Windows is great but that artificial generation of not-needed
> interrupts is avoidable.
> 
> 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), 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. I am aware that some
> changes would be needed in pcm_lib.c, where all the error checks are
> done. Takashi, Jaroslav, Lennart, what do you think?
> Feedback and suggestions welcome.
> Cheers
> - Pierre

How do you handle any clock drift here between the HDA hardware
interface clock and the PA timer ?

Liam

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