diff options
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/hrtimer.c | 121 | ||||
| -rw-r--r-- | kernel/time/clockevents.c | 11 |
2 files changed, 64 insertions, 68 deletions
diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c index 126b980..49da79a 100644 --- a/kernel/hrtimer.c +++ b/kernel/hrtimer.c @@ -191,6 +191,46 @@ struct hrtimer_clock_base *lock_hrtimer_base(const struct hrtimer *timer, } } + +/* + * Get the preferred target CPU for NOHZ + */ +static int hrtimer_get_target(int this_cpu, int pinned) +{ +#ifdef CONFIG_NO_HZ + if (!pinned && get_sysctl_timer_migration() && idle_cpu(this_cpu)) { + int preferred_cpu = get_nohz_load_balancer(); + + if (preferred_cpu >= 0) + return preferred_cpu; + } +#endif + return this_cpu; +} + +/* + * With HIGHRES=y we do not migrate the timer when it is expiring + * before the next event on the target cpu because we cannot reprogram + * the target cpu hardware and we would cause it to fire late. + * + * Called with cpu_base->lock of target cpu held. + */ +static int +hrtimer_check_target(struct hrtimer *timer, struct hrtimer_clock_base *new_base) +{ +#ifdef CONFIG_HIGH_RES_TIMERS + ktime_t expires; + + if (!new_base->cpu_base->hres_active) + return 0; + + expires = ktime_sub(hrtimer_get_expires(timer), new_base->offset); + return expires.tv64 <= new_base->cpu_base->expires_next.tv64; +#else + return 0; +#endif +} + /* * Switch the timer base to the current CPU when possible. */ @@ -200,27 +240,8 @@ switch_hrtimer_base(struct hrtimer *timer, struct hrtimer_clock_base *base, { struct hrtimer_clock_base *new_base; struct hrtimer_cpu_base *new_cpu_base; - int cpu, preferred_cpu = -1; - - cpu = smp_processor_id(); -#if defined(CONFIG_NO_HZ) && defined(CONFIG_SMP) - if (!pinned && get_sysctl_timer_migration() && idle_cpu(cpu)) { - preferred_cpu = get_nohz_load_balancer(); - if (preferred_cpu >= 0) { - /* - * We must not check the expiry value when - * preferred_cpu is the current cpu. If base - * != new_base we would loop forever when the - * timer expires before the current programmed - * next timer event. - */ - if (preferred_cpu != cpu) - cpu = preferred_cpu; - else - preferred_cpu = -1; - } - } -#endif + int this_cpu = smp_processor_id(); + int cpu = hrtimer_get_target(this_cpu, pinned); again: new_cpu_base = &per_cpu(hrtimer_bases, cpu); @@ -228,7 +249,7 @@ again: if (base != new_base) { /* - * We are trying to schedule the timer on the local CPU. + * We are trying to move timer to new_base. * However we can't change timer's base while it is running, * so we keep it on the same CPU. No hassle vs. reprogramming * the event source in the high resolution case. The softirq @@ -244,38 +265,12 @@ again: spin_unlock(&base->cpu_base->lock); spin_lock(&new_base->cpu_base->lock); - /* Optimized away for NOHZ=n SMP=n */ - if (cpu == preferred_cpu) { - /* Calculate clock monotonic expiry time */ -#ifdef CONFIG_HIGH_RES_TIMERS - ktime_t expires = ktime_sub(hrtimer_get_expires(timer), - new_base->offset); -#else - ktime_t expires = hrtimer_get_expires(timer); -#endif - - /* - * Get the next event on target cpu from the - * clock events layer. - * This covers the highres=off nohz=on case as well. - */ - ktime_t next = clockevents_get_next_event(cpu); - - ktime_t delta = ktime_sub(expires, next); - - /* - * We do not migrate the timer when it is expiring - * before the next event on the target cpu because - * we cannot reprogram the target cpu hardware and - * we would cause it to fire late. - */ - if (delta.tv64 < 0) { - cpu = smp_processor_id(); - spin_unlock(&new_base->cpu_base->lock); - spin_lock(&base->cpu_base->lock); - timer->base = base; - goto again; - } + if (cpu != this_cpu && hrtimer_check_target(timer, new_base)) { + cpu = this_cpu; + spin_unlock(&new_base->cpu_base->lock); + spin_lock(&base->cpu_base->lock); + timer->base = base; + goto again; } timer->base = new_base; } @@ -1287,14 +1282,22 @@ void hrtimer_interrupt(struct clock_event_device *dev) expires_next.tv64 = KTIME_MAX; + spin_lock(&cpu_base->lock); + /* + * We set expires_next to KTIME_MAX here with cpu_base->lock + * held to prevent that a timer is enqueued in our queue via + * the migration code. This does not affect enqueueing of + * timers which run their callback and need to be requeued on + * this CPU. + */ + cpu_base->expires_next.tv64 = KTIME_MAX; + base = cpu_base->clock_base; for (i = 0; i < HRTIMER_MAX_CLOCK_BASES; i++) { ktime_t basenow; struct rb_node *node; - spin_lock(&cpu_base->lock); - basenow = ktime_add(now, base->offset); while ((node = base->first)) { @@ -1327,11 +1330,15 @@ void hrtimer_interrupt(struct clock_event_device *dev) __run_hrtimer(timer); } - spin_unlock(&cpu_base->lock); base++; } + /* + * Store the new expiry value so the migration code can verify + * against it. + */ cpu_base->expires_next = expires_next; + spin_unlock(&cpu_base->lock); /* Reprogramming necessary ? */ if (expires_next.tv64 != KTIME_MAX) { diff --git a/kernel/time/clockevents.c b/kernel/time/clockevents.c index 1ad6dd4..a6dcd67 100644 --- a/kernel/time/clockevents.c +++ b/kernel/time/clockevents.c @@ -254,15 +254,4 @@ void clockevents_notify(unsigned long reason, void *arg) spin_unlock(&clockevents_lock); } EXPORT_SYMBOL_GPL(clockevents_notify); - -ktime_t clockevents_get_next_event(int cpu) -{ - struct tick_device *td; - struct clock_event_device *dev; - - td = &per_cpu(tick_cpu_device, cpu); - dev = td->evtdev; - - return dev->next_event; -} #endif |
