From 3f69d04e146c6e14ccdd4e7b37d93f789229202a Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Sun, 25 Feb 2024 23:55:06 +0100 Subject: tick: Shut down low-res tick from dying CPU The timekeeping duty is handed over from the outgoing CPU within stop machine. This works well if CONFIG_NO_HZ_COMMON=n or the tick is in high-res mode. However in low-res dynticks mode, the tick isn't cancelled until the clockevent is shut down, which can happen later. The tick may therefore fire again once IRQs are re-enabled on stop machine and until IRQs are disabled for good upon the last call to idle. That's so many opportunities for a timekeeper to go idle and the outgoing CPU to take over that duty. This is why tick_nohz_idle_stop_tick() is called one last time on idle if the CPU is seen offline: so that the timekeeping duty is handed over again in case the CPU has re-taken the duty. This means there are two timekeeping handovers on CPU down hotplug with different undocumented constraints and purposes: 1) A handover on stop machine for !dynticks || highres. All online CPUs are guaranteed to be non-idle and the timekeeping duty can be safely handed-over. The hrtimer tick is cancelled so it is guaranteed that in dynticks mode the outgoing CPU won't take again the duty. 2) A handover on last idle call for dynticks && lowres. Setting the duty to TICK_DO_TIMER_NONE makes sure that a CPU will take over the timekeeping. Prepare for consolidating the handover to a single place (the first one) with shutting down the low-res tick as well from tick_cancel_sched_timer() as well. This will simplify the handover and unify the tick cancellation between high-res and low-res. Signed-off-by: Frederic Weisbecker Signed-off-by: Thomas Gleixner Reviewed-by: Thomas Gleixner Link: https://lore.kernel.org/r/20240225225508.11587-15-frederic@kernel.org --- kernel/time/tick-common.c | 3 ++- kernel/time/tick-sched.c | 32 +++++++++++++++++++++++++------- kernel/time/tick-sched.h | 4 ++-- 3 files changed, 29 insertions(+), 10 deletions(-) (limited to 'kernel/time') diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c index 522414089c0d..9cd09eea06d6 100644 --- a/kernel/time/tick-common.c +++ b/kernel/time/tick-common.c @@ -410,7 +410,8 @@ int tick_cpu_dying(unsigned int dying_cpu) if (tick_do_timer_cpu == dying_cpu) tick_do_timer_cpu = cpumask_first(cpu_online_mask); - tick_cancel_sched_timer(dying_cpu); + /* Make sure the CPU won't try to retake the timekeeping duty */ + tick_sched_timer_dying(dying_cpu); /* Remove CPU from timer broadcasting */ tick_offline_cpu(dying_cpu); diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index dcb9f0394182..89d16b8ea2c4 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -308,6 +308,14 @@ static enum hrtimer_restart tick_nohz_handler(struct hrtimer *timer) return HRTIMER_RESTART; } +static void tick_sched_timer_cancel(struct tick_sched *ts) +{ + if (tick_sched_flag_test(ts, TS_FLAG_HIGHRES)) + hrtimer_cancel(&ts->sched_timer); + else if (tick_sched_flag_test(ts, TS_FLAG_NOHZ)) + tick_program_event(KTIME_MAX, 1); +} + #ifdef CONFIG_NO_HZ_FULL cpumask_var_t tick_nohz_full_mask; EXPORT_SYMBOL_GPL(tick_nohz_full_mask); @@ -1040,10 +1048,7 @@ static void tick_nohz_stop_tick(struct tick_sched *ts, int cpu) * the tick timer. */ if (unlikely(expires == KTIME_MAX)) { - if (tick_sched_flag_test(ts, TS_FLAG_HIGHRES)) - hrtimer_cancel(&ts->sched_timer); - else - tick_program_event(KTIME_MAX, 1); + tick_sched_timer_cancel(ts); return; } @@ -1598,14 +1603,27 @@ void tick_setup_sched_timer(bool hrtimer) tick_nohz_activate(ts); } -void tick_cancel_sched_timer(int cpu) +/* + * Shut down the tick and make sure the CPU won't try to retake the timekeeping + * duty before disabling IRQs in idle for the last time. + */ +void tick_sched_timer_dying(int cpu) { + struct tick_device *td = &per_cpu(tick_cpu_device, cpu); struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu); + struct clock_event_device *dev = td->evtdev; ktime_t idle_sleeptime, iowait_sleeptime; unsigned long idle_calls, idle_sleeps; - if (tick_sched_flag_test(ts, TS_FLAG_HIGHRES)) - hrtimer_cancel(&ts->sched_timer); + /* This must happen before hrtimers are migrated! */ + tick_sched_timer_cancel(ts); + + /* + * If the clockevents doesn't support CLOCK_EVT_STATE_ONESHOT_STOPPED, + * make sure not to call low-res tick handler. + */ + if (tick_sched_flag_test(ts, TS_FLAG_NOHZ)) + dev->event_handler = clockevents_handle_noop; idle_sleeptime = ts->idle_sleeptime; iowait_sleeptime = ts->iowait_sleeptime; diff --git a/kernel/time/tick-sched.h b/kernel/time/tick-sched.h index bbe72a078985..58d8d1c49dd3 100644 --- a/kernel/time/tick-sched.h +++ b/kernel/time/tick-sched.h @@ -106,9 +106,9 @@ extern struct tick_sched *tick_get_tick_sched(int cpu); extern void tick_setup_sched_timer(bool hrtimer); #if defined CONFIG_NO_HZ_COMMON || defined CONFIG_HIGH_RES_TIMERS -extern void tick_cancel_sched_timer(int cpu); +extern void tick_sched_timer_dying(int cpu); #else -static inline void tick_cancel_sched_timer(int cpu) { } +static inline void tick_sched_timer_dying(int cpu) { } #endif #ifdef CONFIG_GENERIC_CLOCKEVENTS_BROADCAST -- cgit v1.2.3