linux-kernel - [PATCH] clockevent: on resume program the next oneshot tick with the next actual event

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Message-Id: <1237988429-26474-1-git-send-email-Ian.Campbell@citrix.com>
Date:	Wed, 25 Mar 2009 13:40:29 +0000
From:	Ian Campbell <Ian.Campbell@...rix.com>
To:	linux-kernel@...r.kernel.org
Cc:	Ian Campbell <Ian.Campbell@...rix.com>,
	Ian Campbell <ian.campbell@...rix.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	"Alex.Zeffertt" <Alex.Zeffertt@...rix.com>, stable@...nel.org
Subject: [PATCH] clockevent: on resume program the next oneshot tick with the next actual event

When resuming a Xen domU we were seeing an issue where the timer ticks never
seemed to start up again. This was with CONFIG_NO_HZ=y, the Xen clocksource
has CLOCK_EVT_FEAT_ONESHOT but not CLOCK_EVT_FEAT_PERIODIC.

The issue is that on resume tick_resume_oneshot() tries to program an event for
"now", e.g.
	tick_program_event(ktime_get(), 1);

However further down the call chain tick_dev_program_event() then compares that
expiry time with a second call to ktime_get() and discards the event if the
timeout is negative -- which it always will be since some time must have passed
since tick_program_event was called.

Instead of asking for an immediate event on resume, instead ask for the next
actual event.

With this fix I can successfully resume a Xen domain.

Signed-off-by: Ian Campbell <ian.campbell@...rix.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...e.hu>
Cc: Jeremy Fitzhardinge <jeremy@...p.org>
Cc: Alex.Zeffertt <Alex.Zeffertt@...rix.com>
Cc: stable@...nel.org
---
 kernel/time/tick-oneshot.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/kernel/time/tick-oneshot.c b/kernel/time/tick-oneshot.c
index 2e8de67..8b2c8ed 100644
--- a/kernel/time/tick-oneshot.c
+++ b/kernel/time/tick-oneshot.c
@@ -81,7 +81,7 @@ void tick_resume_oneshot(void)
 	struct clock_event_device *dev = td->evtdev;
 
 	clockevents_set_mode(dev, CLOCK_EVT_MODE_ONESHOT);
-	tick_program_event(ktime_get(), 1);
+	tick_program_event(dev->next_event, 1);
 }
 
 /**
-- 
1.5.6.5

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