From: Thomas Gleixner Date: Tue, 26 May 2015 22:50:35 +0000 (+0000) Subject: timer: Minimize nohz off overhead X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=683be13a284720205228e29207ef11a1c3c322b9;p=linux-beck.git timer: Minimize nohz off overhead If nohz is disabled on the kernel command line the [hr]timer code still calls wake_up_nohz_cpu() and tick_nohz_full_cpu(), a pretty pointless exercise. Cache nohz_active in [hr]timer per cpu bases and avoid the overhead. Before: 48.10% hog [.] main 15.25% [kernel] [k] _raw_spin_lock_irqsave 9.76% [kernel] [k] _raw_spin_unlock_irqrestore 6.50% [kernel] [k] mod_timer 6.44% [kernel] [k] lock_timer_base.isra.38 3.87% [kernel] [k] detach_if_pending 3.80% [kernel] [k] del_timer 2.67% [kernel] [k] internal_add_timer 1.33% [kernel] [k] __internal_add_timer 0.73% [kernel] [k] timerfn 0.54% [kernel] [k] wake_up_nohz_cpu After: 48.73% hog [.] main 15.36% [kernel] [k] _raw_spin_lock_irqsave 9.77% [kernel] [k] _raw_spin_unlock_irqrestore 6.61% [kernel] [k] lock_timer_base.isra.38 6.42% [kernel] [k] mod_timer 3.90% [kernel] [k] detach_if_pending 3.76% [kernel] [k] del_timer 2.41% [kernel] [k] internal_add_timer 1.39% [kernel] [k] __internal_add_timer 0.76% [kernel] [k] timerfn We probably should have a cached value for nohz full in the per cpu bases as well to avoid the cpumask check. The base cache line is hot already, the cpumask not necessarily. Signed-off-by: Thomas Gleixner Cc: Peter Zijlstra Cc: Paul McKenney Cc: Frederic Weisbecker Cc: Eric Dumazet Cc: Viresh Kumar Cc: John Stultz Cc: Joonwoo Park Cc: Wenbo Wang Link: http://lkml.kernel.org/r/20150526224512.207378134@linutronix.de Signed-off-by: Thomas Gleixner --- diff --git a/include/linux/hrtimer.h b/include/linux/hrtimer.h index 69551020bb97..76dd4f0da5ca 100644 --- a/include/linux/hrtimer.h +++ b/include/linux/hrtimer.h @@ -164,6 +164,7 @@ enum hrtimer_base_type { * @active_bases: Bitfield to mark bases with active timers * @clock_was_set_seq: Sequence counter of clock was set events * @migration_enabled: The migration of hrtimers to other cpus is enabled + * @nohz_active: The nohz functionality is enabled * @expires_next: absolute time of the next event which was scheduled * via clock_set_next_event() * @next_timer: Pointer to the first expiring timer @@ -188,6 +189,7 @@ struct hrtimer_cpu_base { unsigned int active_bases; unsigned int clock_was_set_seq; bool migration_enabled; + bool nohz_active; #ifdef CONFIG_HIGH_RES_TIMERS unsigned int in_hrtirq : 1, hres_active : 1, diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c index 6115f4df119b..db5c9508ed95 100644 --- a/kernel/time/hrtimer.c +++ b/kernel/time/hrtimer.c @@ -994,7 +994,8 @@ void hrtimer_start_range_ns(struct hrtimer *timer, ktime_t tim, * Kick to reschedule the next tick to handle the new timer * on dynticks target. */ - wake_up_nohz_cpu(new_base->cpu_base->cpu); + if (new_base->cpu_base->nohz_active) + wake_up_nohz_cpu(new_base->cpu_base->cpu); } else { hrtimer_reprogram(timer, new_base); } diff --git a/kernel/time/tick-internal.h b/kernel/time/tick-internal.h index 2edde84744df..966a5a6fdd0a 100644 --- a/kernel/time/tick-internal.h +++ b/kernel/time/tick-internal.h @@ -156,9 +156,9 @@ extern unsigned long tick_nohz_active; #endif #if defined(CONFIG_SMP) && defined(CONFIG_NO_HZ_COMMON) -extern void timers_update_migration(void); +extern void timers_update_migration(bool update_nohz); #else -static inline void timers_update_migration(void) { } +static inline void timers_update_migration(bool update_nohz) { } #endif DECLARE_PER_CPU(struct hrtimer_cpu_base, hrtimer_bases); diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index b1cb01699355..c792429e98c6 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -963,7 +963,7 @@ static inline void tick_nohz_activate(struct tick_sched *ts, int mode) ts->nohz_mode = mode; /* One update is enough */ if (!test_and_set_bit(0, &tick_nohz_active)) - timers_update_migration(); + timers_update_migration(true); } /** diff --git a/kernel/time/timer.c b/kernel/time/timer.c index 343142ed996a..520499dd85af 100644 --- a/kernel/time/timer.c +++ b/kernel/time/timer.c @@ -86,6 +86,7 @@ struct tvec_base { unsigned long all_timers; int cpu; bool migration_enabled; + bool nohz_active; struct tvec_root tv1; struct tvec tv2; struct tvec tv3; @@ -99,7 +100,7 @@ static DEFINE_PER_CPU(struct tvec_base, tvec_bases); #if defined(CONFIG_SMP) && defined(CONFIG_NO_HZ_COMMON) unsigned int sysctl_timer_migration = 1; -void timers_update_migration(void) +void timers_update_migration(bool update_nohz) { bool on = sysctl_timer_migration && tick_nohz_active; unsigned int cpu; @@ -111,6 +112,10 @@ void timers_update_migration(void) for_each_possible_cpu(cpu) { per_cpu(tvec_bases.migration_enabled, cpu) = on; per_cpu(hrtimer_bases.migration_enabled, cpu) = on; + if (!update_nohz) + continue; + per_cpu(tvec_bases.nohz_active, cpu) = true; + per_cpu(hrtimer_bases.nohz_active, cpu) = true; } } @@ -124,7 +129,7 @@ int timer_migration_handler(struct ctl_table *table, int write, mutex_lock(&mutex); ret = proc_dointvec(table, write, buffer, lenp, ppos); if (!ret && write) - timers_update_migration(); + timers_update_migration(false); mutex_unlock(&mutex); return ret; } @@ -436,8 +441,11 @@ static void internal_add_timer(struct tvec_base *base, struct timer_list *timer) * require special care against races with idle_cpu(), lets deal * with that later. */ - if (!(timer->flags & TIMER_DEFERRABLE) || tick_nohz_full_cpu(base->cpu)) - wake_up_nohz_cpu(base->cpu); + if (base->nohz_active) { + if (!(timer->flags & TIMER_DEFERRABLE) || + tick_nohz_full_cpu(base->cpu)) + wake_up_nohz_cpu(base->cpu); + } } #ifdef CONFIG_TIMER_STATS