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

[Arun Raghavan]

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>

> 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);