diff options
| -rw-r--r-- | kernel/time/tick-internal.h | 1 | ||||
| -rw-r--r-- | kernel/time/tick-sched.c | 12 | ||||
| -rw-r--r-- | kernel/time/timer.c | 128 |
3 files changed, 120 insertions, 21 deletions
diff --git a/kernel/time/tick-internal.h b/kernel/time/tick-internal.h index 966a5a6fdd0a..f738251000fe 100644 --- a/kernel/time/tick-internal.h +++ b/kernel/time/tick-internal.h @@ -164,3 +164,4 @@ static inline void timers_update_migration(bool update_nohz) { } DECLARE_PER_CPU(struct hrtimer_cpu_base, hrtimer_bases); extern u64 get_next_timer_interrupt(unsigned long basej, u64 basem); +void timer_clear_idle(void); diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index 69abc7bfe80f..5d81f9aa30d2 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -700,6 +700,12 @@ static ktime_t tick_nohz_stop_sched_tick(struct tick_sched *ts, delta = next_tick - basemono; if (delta <= (u64)TICK_NSEC) { tick.tv64 = 0; + + /* + * Tell the timer code that the base is not idle, i.e. undo + * the effect of get_next_timer_interrupt(): + */ + timer_clear_idle(); /* * We've not stopped the tick yet, and there's a timer in the * next period, so no point in stopping it either, bail. @@ -809,6 +815,12 @@ static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now) tick_do_update_jiffies64(now); cpu_load_update_nohz_stop(); + /* + * Clear the timer idle flag, so we avoid IPIs on remote queueing and + * the clock forward checks in the enqueue path: + */ + timer_clear_idle(); + calc_load_exit_idle(); touch_softlockup_watchdog_sched(); /* diff --git a/kernel/time/timer.c b/kernel/time/timer.c index 658051c97a3c..9339d71ee998 100644 --- a/kernel/time/timer.c +++ b/kernel/time/timer.c @@ -196,9 +196,11 @@ struct timer_base { spinlock_t lock; struct timer_list *running_timer; unsigned long clk; + unsigned long next_expiry; unsigned int cpu; bool migration_enabled; bool nohz_active; + bool is_idle; DECLARE_BITMAP(pending_map, WHEEL_SIZE); struct hlist_head vectors[WHEEL_SIZE]; } ____cacheline_aligned; @@ -519,24 +521,37 @@ static void internal_add_timer(struct timer_base *base, struct timer_list *timer { __internal_add_timer(base, timer); + if (!IS_ENABLED(CONFIG_NO_HZ_COMMON) || !base->nohz_active) + return; + /* - * Check whether the other CPU is in dynticks mode and needs - * to be triggered to reevaluate the timer wheel. We are - * protected against the other CPU fiddling with the timer by - * holding the timer base lock. This also makes sure that a - * CPU on the way to stop its tick can not evaluate the timer - * wheel. - * - * Spare the IPI for deferrable timers on idle targets though. - * The next busy ticks will take care of it. Except full dynticks - * require special care against races with idle_cpu(), lets deal - * with that later. + * TODO: This wants some optimizing similar to the code below, but we + * will do that when we switch from push to pull for deferrable timers. */ - if (IS_ENABLED(CONFIG_NO_HZ_COMMON) && base->nohz_active) { - if (!(timer->flags & TIMER_DEFERRABLE) || - tick_nohz_full_cpu(base->cpu)) + if (timer->flags & TIMER_DEFERRABLE) { + if (tick_nohz_full_cpu(base->cpu)) wake_up_nohz_cpu(base->cpu); + return; } + + /* + * We might have to IPI the remote CPU if the base is idle and the + * timer is not deferrable. If the other CPU is on the way to idle + * then it can't set base->is_idle as we hold the base lock: + */ + if (!base->is_idle) + return; + + /* Check whether this is the new first expiring timer: */ + if (time_after_eq(timer->expires, base->next_expiry)) + return; + + /* + * Set the next expiry time and kick the CPU so it can reevaluate the + * wheel: + */ + base->next_expiry = timer->expires; + wake_up_nohz_cpu(base->cpu); } #ifdef CONFIG_TIMER_STATS @@ -844,10 +859,11 @@ static inline struct timer_base *get_timer_base(u32 tflags) return get_timer_cpu_base(tflags, tflags & TIMER_CPUMASK); } -static inline struct timer_base *get_target_base(struct timer_base *base, - unsigned tflags) +#ifdef CONFIG_NO_HZ_COMMON +static inline struct timer_base * +__get_target_base(struct timer_base *base, unsigned tflags) { -#if defined(CONFIG_NO_HZ_COMMON) && defined(CONFIG_SMP) +#ifdef CONFIG_SMP if ((tflags & TIMER_PINNED) || !base->migration_enabled) return get_timer_this_cpu_base(tflags); return get_timer_cpu_base(tflags, get_nohz_timer_target()); @@ -856,6 +872,43 @@ static inline struct timer_base *get_target_base(struct timer_base *base, #endif } +static inline void forward_timer_base(struct timer_base *base) +{ + /* + * We only forward the base when it's idle and we have a delta between + * base clock and jiffies. + */ + if (!base->is_idle || (long) (jiffies - base->clk) < 2) + return; + + /* + * If the next expiry value is > jiffies, then we fast forward to + * jiffies otherwise we forward to the next expiry value. + */ + if (time_after(base->next_expiry, jiffies)) + base->clk = jiffies; + else + base->clk = base->next_expiry; +} +#else +static inline struct timer_base * +__get_target_base(struct timer_base *base, unsigned tflags) +{ + return get_timer_this_cpu_base(tflags); +} + +static inline void forward_timer_base(struct timer_base *base) { } +#endif + +static inline struct timer_base * +get_target_base(struct timer_base *base, unsigned tflags) +{ + struct timer_base *target = __get_target_base(base, tflags); + + forward_timer_base(target); + return target; +} + /* * We are using hashed locking: Holding per_cpu(timer_bases[x]).lock means * that all timers which are tied to this base are locked, and the base itself @@ -1417,16 +1470,49 @@ u64 get_next_timer_interrupt(unsigned long basej, u64 basem) spin_lock(&base->lock); nextevt = __next_timer_interrupt(base); - spin_unlock(&base->lock); + base->next_expiry = nextevt; + /* + * We have a fresh next event. Check whether we can forward the base: + */ + if (time_after(nextevt, jiffies)) + base->clk = jiffies; + else if (time_after(nextevt, base->clk)) + base->clk = nextevt; - if (time_before_eq(nextevt, basej)) + if (time_before_eq(nextevt, basej)) { expires = basem; - else + base->is_idle = false; + } else { expires = basem + (nextevt - basej) * TICK_NSEC; + /* + * If we expect to sleep more than a tick, mark the base idle: + */ + if ((expires - basem) > TICK_NSEC) + base->is_idle = true; + } + spin_unlock(&base->lock); return cmp_next_hrtimer_event(basem, expires); } +/** + * timer_clear_idle - Clear the idle state of the timer base + * + * Called with interrupts disabled + */ +void timer_clear_idle(void) +{ + struct timer_base *base = this_cpu_ptr(&timer_bases[BASE_STD]); + + /* + * We do this unlocked. The worst outcome is a remote enqueue sending + * a pointless IPI, but taking the lock would just make the window for + * sending the IPI a few instructions smaller for the cost of taking + * the lock in the exit from idle path. + */ + base->is_idle = false; +} + static int collect_expired_timers(struct timer_base *base, struct hlist_head *heads) { @@ -1440,7 +1526,7 @@ static int collect_expired_timers(struct timer_base *base, /* * If the next timer is ahead of time forward to current - * jiffies, otherwise forward to the next expiry time. + * jiffies, otherwise forward to the next expiry time: */ if (time_after(next, jiffies)) { /* The call site will increment clock! */ |