From eaa907c546f76222227dfc41784b22588af1e3d7 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Wed, 6 Mar 2013 11:18:36 +0000 Subject: [PATCH] tick: Provide a check for a forced broadcast pending On the CPU which gets woken along with the target CPU of the broadcast the following happens: deep_idle() <-- spurious wakeup broadcast_exit() set forced bit enable interrupts <-- Nothing happens disable interrupts broadcast_enter() <-- Here we observe the forced bit is set deep_idle() Now after that the target CPU of the broadcast runs the broadcast handler and finds the other CPU in both the broadcast and the forced mask, sends the IPI and stuff gets back to normal. So it's not actually harmful, just more evidence for the theory, that hardware designers have access to very special drug supplies. Now there is no point in going back to deep idle just to wake up again right away via an IPI. Provide a check which allows the idle code to avoid the deep idle transition. Signed-off-by: Thomas Gleixner Cc: LAK Cc: John Stultz Cc: Arjan van de Veen Cc: Lorenzo Pieralisi Tested-by: Santosh Shilimkar Cc: Jason Liu Link: http://lkml.kernel.org/r/20130306111537.565418308@linutronix.de Signed-off-by: Thomas Gleixner --- include/linux/clockchips.h | 6 ++++++ kernel/time/tick-broadcast.c | 12 ++++++++++++ 2 files changed, 18 insertions(+) diff --git a/include/linux/clockchips.h b/include/linux/clockchips.h index 494d33ea78f8..646aac136eed 100644 --- a/include/linux/clockchips.h +++ b/include/linux/clockchips.h @@ -175,6 +175,12 @@ extern void tick_broadcast(const struct cpumask *mask); extern int tick_receive_broadcast(void); #endif +#if defined(CONFIG_GENERIC_CLOCKEVENTS_BROADCAST) && defined(CONFIG_TICK_ONESHOT) +extern int tick_check_broadcast_expired(void); +#else +static inline int tick_check_broadcast_expired(void) { return 0; } +#endif + #ifdef CONFIG_GENERIC_CLOCKEVENTS extern void clockevents_notify(unsigned long reason, void *arg); #else diff --git a/kernel/time/tick-broadcast.c b/kernel/time/tick-broadcast.c index 2100aad6b5f2..d76d816afc5d 100644 --- a/kernel/time/tick-broadcast.c +++ b/kernel/time/tick-broadcast.c @@ -403,6 +403,18 @@ struct cpumask *tick_get_broadcast_oneshot_mask(void) return tick_broadcast_oneshot_mask; } +/* + * Called before going idle with interrupts disabled. Checks whether a + * broadcast event from the other core is about to happen. We detected + * that in tick_broadcast_oneshot_control(). The callsite can use this + * to avoid a deep idle transition as we are about to get the + * broadcast IPI right away. + */ +int tick_check_broadcast_expired(void) +{ + return cpumask_test_cpu(smp_processor_id(), tick_broadcast_force_mask); +} + /* * Set broadcast interrupt affinity */