linux-kernel - [045/115] ALSA: hrtimer: handle delayed timer interrupts

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Date:	Tue, 15 Feb 2011 17:45:11 -0800
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Clemens Ladisch <clemens@...isch.de>,
	Takashi Iwai <tiwai@...e.de>
Subject: [045/115] ALSA: hrtimer: handle delayed timer interrupts

2.6.32-longterm review patch.  If anyone has any objections, please let us know.

------------------

From: Clemens Ladisch <clemens@...isch.de>

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@...isch.de>
Reported-and-tested-by: Arthur Marsh <arthur.marsh@...ernode.on.net>
Signed-off-by: Takashi Iwai <tiwai@...e.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

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

--- a/sound/core/hrtimer.c
+++ b/sound/core/hrtimer.c
@@ -44,12 +44,13 @@ static enum hrtimer_restart snd_hrtimer_
 {
 	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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