From 70e5975d3a04be5479a28eec4a2fb10f98ad2785 Mon Sep 17 00:00:00 2001 From: Stephen Boyd Date: Thu, 13 Jun 2013 11:39:50 -0700 Subject: clockevents: Prefer CPU local devices over global devices On an SMP system with only one global clockevent and a dummy clockevent per CPU we run into problems. We want the dummy clockevents to be registered as the per CPU tick devices, but we can only achieve that if we register the dummy clockevents before the global clockevent or if we artificially inflate the rating of the dummy clockevents to be higher than the rating of the global clockevent. Failure to do so leads to boot hangs when the dummy timers are registered on all other CPUs besides the CPU that accepted the global clockevent as its tick device and there is no broadcast timer to poke the dummy devices. If we're registering multiple clockevents and one clockevent is global and the other is local to a particular CPU we should choose to use the local clockevent regardless of the rating of the device. This way, if the clockevent is a dummy it will take the tick device duty as long as there isn't a higher rated tick device and any global clockevent will be bumped out into broadcast mode, fixing the problem described above. Reported-and-tested-by: Mark Rutland Signed-off-by: Stephen Boyd Tested-by: soren.brinkmann@xilinx.com Cc: John Stultz Cc: Daniel Lezcano Cc: linux-arm-kernel@lists.infradead.org Cc: John Stultz Link: http://lkml.kernel.org/r/20130613183950.GA32061@codeaurora.org Signed-off-by: Thomas Gleixner --- kernel/time/tick-common.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) (limited to 'kernel') diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c index 5edfb4806032..edd45f64162f 100644 --- a/kernel/time/tick-common.c +++ b/kernel/time/tick-common.c @@ -243,8 +243,13 @@ static bool tick_check_preferred(struct clock_event_device *curdev, return false; } - /* Use the higher rated one */ - return !curdev || newdev->rating > curdev->rating; + /* + * Use the higher rated one, but prefer a CPU local device with a lower + * rating than a non-CPU local device + */ + return !curdev || + newdev->rating > curdev->rating || + !cpumask_equal(curdev->cpumask, newdev->cpumask); } /* -- cgit v1.2.3