[alsa-devel] [PATCH] ALSA: HDA: Lessen CPU usage when waiting for chip to respond

[Takashi Iwai]

At Wed, 09 May 2012 01:35:52 +0530,
Arun Raghavan wrote:
> 
> On Fri, 2012-05-04 at 11:05 +0200, David Henningsson wrote:
> > When an IRQ for some reason gets lost, we wait up to a second using
> > udelay, which is CPU intensive. This patch improves the situation by
> > waiting about 30 ms in the CPU intensive mode, then stepping down to
> > using msleep(2) instead. In essence, we trade some granularity in
> > exchange for less CPU consumption when the waiting time is a bit longer.
> > 
> > As a result, PulseAudio should no longer be killed by the kernel
> > for taking up to much RT-prio CPU time. At least not for *this* reason.
> > 
> > Signed-off-by: David Henningsson <david.henningsson at canonical.com>
> > ---
> >  sound/pci/hda/hda_intel.c |    6 ++++--
> >  1 file changed, 4 insertions(+), 2 deletions(-)
> > 
> > Hi Arun,
> > 
> > Can you check if this patch resolves your problem with PulseAudio getting
> > killed by the kernel? If so, we should apply it to the kernel, perhaps even
> > to stable.
> > 
> > // David
> 
> Thanks, this fixes the problem for me. Don't know what the official
> procedure for these things is, but fwiw:
> 
> Signed-off-by: Arun Raghavan <arun.raghavan at collabora.co.uk>

I guess you meant tested-by tag?
In anyway I took the patch now with Cc to stable.  It'll be included
in the next pull request to Linus.


thanks,

Takashi

> 
> > diff --git a/sound/pci/hda/hda_intel.c b/sound/pci/hda/hda_intel.c
> > index 7b6a823..0e7c3f1 100644
> > --- a/sound/pci/hda/hda_intel.c
> > +++ b/sound/pci/hda/hda_intel.c
> > @@ -783,11 +783,13 @@ static unsigned int azx_rirb_get_response(struct hda_bus *bus,
> >  {
> >  	struct azx *chip = bus->private_data;
> >  	unsigned long timeout;
> > +	unsigned long loopcounter;
> >  	int do_poll = 0;
> >  
> >   again:
> >  	timeout = jiffies + msecs_to_jiffies(1000);
> > -	for (;;) {
> > +	
> > +	for (loopcounter = 0;; loopcounter++) {
> >  		if (chip->polling_mode || do_poll) {
> >  			spin_lock_irq(&chip->reg_lock);
> >  			azx_update_rirb(chip);
> > @@ -803,7 +805,7 @@ static unsigned int azx_rirb_get_response(struct hda_bus *bus,
> >  		}
> >  		if (time_after(jiffies, timeout))
> >  			break;
> > -		if (bus->needs_damn_long_delay)
> > +		if (bus->needs_damn_long_delay || loopcounter > 3000)
> >  			msleep(2); /* temporary workaround */
> >  		else {
> >  			udelay(10);
> 
> 
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