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

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Message-Id: <20110330210444.3A55F3E1A05@tassilo.jf.intel.com>
Date:	Wed, 30 Mar 2011 14:04:44 -0700 (PDT)
From:	Andi Kleen <andi@...stfloor.org>
To:	clemens@...isch.de, ak@...ux.intel.com, tiwai@...e.de,
	gregkh@...e.de, linux-kernel@...r.kernel.org, stable@...nel.org,
	tim.bird@...sony.com
Subject: [PATCH] [48/275] ALSA: hrtimer: handle delayed timer interrupts

2.6.35-longterm review patch.  If anyone has any objections, please let me 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>
Signed-off-by: Andi Kleen <ak@...ux.intel.com>
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(-)

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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