On 04/09/13 03:33, Mark Rutland wrote: > On Mon, Apr 08, 2013 at 10:27:23PM +0100, Stephen Boyd wrote: >> 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. > It might be worth pointing out that if dummy timers are only registered > when there's more than one CPU, UP behaviour won't degrade from the > current state of affairs. Sure, I'll try to come up with something if I have to repost (looks like I might have to rework the mct change). > >> Reported-by: Mark Rutland <mark.rutland@xxxxxxx> >> Cc: John Stultz <john.stultz@xxxxxxxxxx> >> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> >> Signed-off-by: Stephen Boyd <sboyd@xxxxxxxxxxxxxx> >> --- >> kernel/time/tick-common.c | 5 +++-- >> 1 file changed, 3 insertions(+), 2 deletions(-) >> >> diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c >> index b1600a6..9ea59b9 100644 >> --- a/kernel/time/tick-common.c >> +++ b/kernel/time/tick-common.c >> @@ -251,9 +251,10 @@ static int tick_check_new_device(struct clock_event_device *newdev) >> !(newdev->features & CLOCK_EVT_FEAT_ONESHOT)) >> goto out_bc; >> /* >> - * Check the rating >> + * Check the rating, but prefer CPU local devices >> */ >> - if (curdev->rating >= newdev->rating) >> + if (curdev->rating >= newdev->rating && >> + cpumask_equal(curdev->cpumask, newdev->cpumask)) >> goto out_bc; >> } > This looks good to me. I tested this on a TC2 with a v3.9-rc6 kernel > without architected timer support. The patch restores the ability to use > the sp804 as a broadcast source. > > Tested-by: Mark Rutland <mark.rutland@xxxxxxx> > > If possible I think this should sit in -next for a bit to make sure it > doesn't have any unexpected side effects. Thanks for testing. -- Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation -- To unsubscribe from this list: send the line "unsubscribe linux-arm-msm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
