[PATCH] [48/275] ALSA: hrtimer: handle delayed timer interrupts

[Andi Kleen]

2.6.35-longterm review patch.  If anyone has any objections, please let me know.

------------------
From: Clemens Ladisch <clemens@xxxxxxxxxx>

commit b1d4f7f4bdcf9915c41ff8cfc4425c84dabb1fde upstream.

If a timer interrupt was delayed too much, hrtimer_forward_now() will
forward the timer expiry more than once.  When this happens, the
additional number of elapsed ALSA timer ticks must be passed to
snd_timer_interrupt() to prevent the ALSA timer from falling behind.

This mostly fixes MIDI slowdown problems on highly-loaded systems with
badly behaved interrupt handlers.

Signed-off-by: Clemens Ladisch <clemens@xxxxxxxxxx>
Signed-off-by: Andi Kleen <ak@xxxxxxxxxxxxxxx>
Reported-and-tested-by: Arthur Marsh <arthur.marsh@xxxxxxxxxxxxxxxx>
Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

---
 sound/core/hrtimer.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

Index: linux-2.6.35.y/sound/core/hrtimer.c
===================================================================
--- linux-2.6.35.y.orig/sound/core/hrtimer.c	2011-03-29 22:51:50.260437129 -0700
+++ linux-2.6.35.y/sound/core/hrtimer.c	2011-03-29 23:02:59.176321246 -0700
@@ -45,12 +45,13 @@
 {
 	struct snd_hrtimer *stime = container_of(hrt, struct snd_hrtimer, hrt);
 	struct snd_timer *t = stime->timer;
+	unsigned long oruns;
 
 	if (!atomic_read(&stime->running))
 		return HRTIMER_NORESTART;
 
-	hrtimer_forward_now(hrt, ns_to_ktime(t->sticks * resolution));
-	snd_timer_interrupt(stime->timer, t->sticks);
+	oruns = hrtimer_forward_now(hrt, ns_to_ktime(t->sticks * resolution));
+	snd_timer_interrupt(stime->timer, t->sticks * oruns);
 
 	if (!atomic_read(&stime->running))
 		return HRTIMER_NORESTART;
--
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