From 683be13a284720205228e29207ef11a1c3c322b9 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Tue, 26 May 2015 22:50:35 +0000 Subject: 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 --- kernel/time/timer.c | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-) (limited to 'kernel/time/timer.c') 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 -- cgit v1.2.3