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Some brilliant hardware implementations wake multiple cores when the broadcast timer fires. This leads to the following interesting problem: CPU0 CPU1 wakeup from idle wakeup from idle leave broadcast mode leave broadcast mode restart per cpu timer restart per cpu timer go back to idle handle broadcast (empty mask) enter broadcast mode programm broadcast device enter broadcast mode programm broadcast device So what happens is that due to the forced reprogramming of the cpu local timer, we need to set a event in the future. Now if we manage to go back to idle before the timer fires, we switch off the timer and arm the broadcast device with an already expired time (covered by forced mode). So in the worst case we repeat the above ping pong forever. Unfortunately we have no information about what caused the wakeup, but we can check current time against the expiry time of the local cpu. If the local event is already in the past, we know that the broadcast timer is about to fire and send an IPI. So we mark ourself as an IPI target even if we left broadcast mode and avoid the reprogramming of the local cpu timer. This still leaves the possibility that a CPU which is not handling the broadcast interrupt is going to reach idle again before the IPI arrives. This can't be solved in the core code and will be handled in follow up patches. Reported-by: Jason Liu <liu.h.jason@gmail.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: LAK <linux-arm-kernel@lists.infradead.org> Cc: John Stultz <john.stultz@linaro.org> Cc: Arjan van de Veen <arjan@infradead.org> Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com> Tested-by: Santosh Shilimkar <santosh.shilimkar@ti.com> Link: http://lkml.kernel.org/r/20130306111537.492045206@linutronix.de Signed-off-by: Thomas Gleixner <tglx@linutronix.de> |
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| .. | ||
| alarmtimer.c | ||
| clockevents.c | ||
| clocksource.c | ||
| jiffies.c | ||
| Kconfig | ||
| Makefile | ||
| ntp.c | ||
| posix-clock.c | ||
| tick-broadcast.c | ||
| tick-common.c | ||
| tick-internal.h | ||
| tick-oneshot.c | ||
| tick-sched.c | ||
| timeconv.c | ||
| timekeeping.c | ||
| timer_list.c | ||
| timer_stats.c | ||