Commit c038c1c4 authored Apr 17, 2013 by Stephen Boyd Committed by Thomas Gleixner Apr 17, 2013

clockevents: Switch into oneshot mode even if broadcast registered late



tick_oneshot_notify() is used to notify a particular CPU to try
to switch into oneshot mode after a oneshot capable tick device
is registered and tick_clock_notify() is used to notify all CPUs
to try to switch into oneshot mode after a high res clocksource
is registered. There is one caveat; if the tick devices suffer
from FEAT_C3_STOP we don't try to switch into oneshot mode unless
we have a oneshot capable broadcast device already registered.

If the broadcast device is registered after the tick devices that
have FEAT_C3_STOP we'll never try to switch into oneshot mode
again, causing us to be stuck in periodic mode forever. Avoid
this scenario by calling tick_clock_notify() after we register
the broadcast device so that we try to switch into oneshot mode
on all CPUs one more time.

[ tglx: Adopted to timers/core and added a comment ]

Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Link: http://lkml.kernel.org/r/1366219566-29783-1-git-send-email-sboyd@codeaurora.org


Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

parent b3956a89

kernel/time/tick-broadcast.c

+10 −0

Original line number	Diff line number	Diff line
		@@ -75,6 +75,16 @@ int tick_check_broadcast_device(struct clock_event_device *dev)
		tick_broadcast_device.evtdev = dev;
		if (!cpumask_empty(tick_broadcast_mask))
		tick_broadcast_start_periodic(dev);
		/*
		* Inform all cpus about this. We might be in a situation
		* where we did not switch to oneshot mode because the per cpu
		* devices are affected by CLOCK_EVT_FEAT_C3STOP and the lack
		* of a oneshot capable broadcast device. Without that
		* notification the systems stays stuck in periodic mode
		* forever.
		*/
		if (dev->features & CLOCK_EVT_FEAT_ONESHOT)
		tick_clock_notify();
		return 1;
		}