diff options
Diffstat (limited to 'kernel/time/timer.c')
| -rw-r--r-- | kernel/time/timer.c | 1133 |
1 files changed, 672 insertions, 461 deletions
diff --git a/kernel/time/timer.c b/kernel/time/timer.c index 3a95f9728..32bf6f75a 100644 --- a/kernel/time/timer.c +++ b/kernel/time/timer.c @@ -59,43 +59,153 @@ __visible u64 jiffies_64 __cacheline_aligned_in_smp = INITIAL_JIFFIES; EXPORT_SYMBOL(jiffies_64); /* - * per-CPU timer vector definitions: + * The timer wheel has LVL_DEPTH array levels. Each level provides an array of + * LVL_SIZE buckets. Each level is driven by its own clock and therefor each + * level has a different granularity. + * + * The level granularity is: LVL_CLK_DIV ^ lvl + * The level clock frequency is: HZ / (LVL_CLK_DIV ^ level) + * + * The array level of a newly armed timer depends on the relative expiry + * time. The farther the expiry time is away the higher the array level and + * therefor the granularity becomes. + * + * Contrary to the original timer wheel implementation, which aims for 'exact' + * expiry of the timers, this implementation removes the need for recascading + * the timers into the lower array levels. The previous 'classic' timer wheel + * implementation of the kernel already violated the 'exact' expiry by adding + * slack to the expiry time to provide batched expiration. The granularity + * levels provide implicit batching. + * + * This is an optimization of the original timer wheel implementation for the + * majority of the timer wheel use cases: timeouts. The vast majority of + * timeout timers (networking, disk I/O ...) are canceled before expiry. If + * the timeout expires it indicates that normal operation is disturbed, so it + * does not matter much whether the timeout comes with a slight delay. + * + * The only exception to this are networking timers with a small expiry + * time. They rely on the granularity. Those fit into the first wheel level, + * which has HZ granularity. + * + * We don't have cascading anymore. timers with a expiry time above the + * capacity of the last wheel level are force expired at the maximum timeout + * value of the last wheel level. From data sampling we know that the maximum + * value observed is 5 days (network connection tracking), so this should not + * be an issue. + * + * The currently chosen array constants values are a good compromise between + * array size and granularity. + * + * This results in the following granularity and range levels: + * + * HZ 1000 steps + * Level Offset Granularity Range + * 0 0 1 ms 0 ms - 63 ms + * 1 64 8 ms 64 ms - 511 ms + * 2 128 64 ms 512 ms - 4095 ms (512ms - ~4s) + * 3 192 512 ms 4096 ms - 32767 ms (~4s - ~32s) + * 4 256 4096 ms (~4s) 32768 ms - 262143 ms (~32s - ~4m) + * 5 320 32768 ms (~32s) 262144 ms - 2097151 ms (~4m - ~34m) + * 6 384 262144 ms (~4m) 2097152 ms - 16777215 ms (~34m - ~4h) + * 7 448 2097152 ms (~34m) 16777216 ms - 134217727 ms (~4h - ~1d) + * 8 512 16777216 ms (~4h) 134217728 ms - 1073741822 ms (~1d - ~12d) + * + * HZ 300 + * Level Offset Granularity Range + * 0 0 3 ms 0 ms - 210 ms + * 1 64 26 ms 213 ms - 1703 ms (213ms - ~1s) + * 2 128 213 ms 1706 ms - 13650 ms (~1s - ~13s) + * 3 192 1706 ms (~1s) 13653 ms - 109223 ms (~13s - ~1m) + * 4 256 13653 ms (~13s) 109226 ms - 873810 ms (~1m - ~14m) + * 5 320 109226 ms (~1m) 873813 ms - 6990503 ms (~14m - ~1h) + * 6 384 873813 ms (~14m) 6990506 ms - 55924050 ms (~1h - ~15h) + * 7 448 6990506 ms (~1h) 55924053 ms - 447392423 ms (~15h - ~5d) + * 8 512 55924053 ms (~15h) 447392426 ms - 3579139406 ms (~5d - ~41d) + * + * HZ 250 + * Level Offset Granularity Range + * 0 0 4 ms 0 ms - 255 ms + * 1 64 32 ms 256 ms - 2047 ms (256ms - ~2s) + * 2 128 256 ms 2048 ms - 16383 ms (~2s - ~16s) + * 3 192 2048 ms (~2s) 16384 ms - 131071 ms (~16s - ~2m) + * 4 256 16384 ms (~16s) 131072 ms - 1048575 ms (~2m - ~17m) + * 5 320 131072 ms (~2m) 1048576 ms - 8388607 ms (~17m - ~2h) + * 6 384 1048576 ms (~17m) 8388608 ms - 67108863 ms (~2h - ~18h) + * 7 448 8388608 ms (~2h) 67108864 ms - 536870911 ms (~18h - ~6d) + * 8 512 67108864 ms (~18h) 536870912 ms - 4294967288 ms (~6d - ~49d) + * + * HZ 100 + * Level Offset Granularity Range + * 0 0 10 ms 0 ms - 630 ms + * 1 64 80 ms 640 ms - 5110 ms (640ms - ~5s) + * 2 128 640 ms 5120 ms - 40950 ms (~5s - ~40s) + * 3 192 5120 ms (~5s) 40960 ms - 327670 ms (~40s - ~5m) + * 4 256 40960 ms (~40s) 327680 ms - 2621430 ms (~5m - ~43m) + * 5 320 327680 ms (~5m) 2621440 ms - 20971510 ms (~43m - ~5h) + * 6 384 2621440 ms (~43m) 20971520 ms - 167772150 ms (~5h - ~1d) + * 7 448 20971520 ms (~5h) 167772160 ms - 1342177270 ms (~1d - ~15d) */ -#define TVN_BITS (CONFIG_BASE_SMALL ? 4 : 6) -#define TVR_BITS (CONFIG_BASE_SMALL ? 6 : 8) -#define TVN_SIZE (1 << TVN_BITS) -#define TVR_SIZE (1 << TVR_BITS) -#define TVN_MASK (TVN_SIZE - 1) -#define TVR_MASK (TVR_SIZE - 1) -#define MAX_TVAL ((unsigned long)((1ULL << (TVR_BITS + 4*TVN_BITS)) - 1)) - -struct tvec { - struct hlist_head vec[TVN_SIZE]; -}; -struct tvec_root { - struct hlist_head vec[TVR_SIZE]; -}; +/* Clock divisor for the next level */ +#define LVL_CLK_SHIFT 3 +#define LVL_CLK_DIV (1UL << LVL_CLK_SHIFT) +#define LVL_CLK_MASK (LVL_CLK_DIV - 1) +#define LVL_SHIFT(n) ((n) * LVL_CLK_SHIFT) +#define LVL_GRAN(n) (1UL << LVL_SHIFT(n)) -struct tvec_base { - spinlock_t lock; - struct timer_list *running_timer; - unsigned long timer_jiffies; - unsigned long next_timer; - unsigned long active_timers; - unsigned long all_timers; - int cpu; - bool migration_enabled; - bool nohz_active; - struct tvec_root tv1; - struct tvec tv2; - struct tvec tv3; - struct tvec tv4; - struct tvec tv5; -} ____cacheline_aligned; +/* + * The time start value for each level to select the bucket at enqueue + * time. + */ +#define LVL_START(n) ((LVL_SIZE - 1) << (((n) - 1) * LVL_CLK_SHIFT)) + +/* Size of each clock level */ +#define LVL_BITS 6 +#define LVL_SIZE (1UL << LVL_BITS) +#define LVL_MASK (LVL_SIZE - 1) +#define LVL_OFFS(n) ((n) * LVL_SIZE) + +/* Level depth */ +#if HZ > 100 +# define LVL_DEPTH 9 +# else +# define LVL_DEPTH 8 +#endif + +/* The cutoff (max. capacity of the wheel) */ +#define WHEEL_TIMEOUT_CUTOFF (LVL_START(LVL_DEPTH)) +#define WHEEL_TIMEOUT_MAX (WHEEL_TIMEOUT_CUTOFF - LVL_GRAN(LVL_DEPTH - 1)) + +/* + * The resulting wheel size. If NOHZ is configured we allocate two + * wheels so we have a separate storage for the deferrable timers. + */ +#define WHEEL_SIZE (LVL_SIZE * LVL_DEPTH) + +#ifdef CONFIG_NO_HZ_COMMON +# define NR_BASES 2 +# define BASE_STD 0 +# define BASE_DEF 1 +#else +# define NR_BASES 1 +# define BASE_STD 0 +# define BASE_DEF 0 +#endif +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; -static DEFINE_PER_CPU(struct tvec_base, tvec_bases); +static DEFINE_PER_CPU(struct timer_base, timer_bases[NR_BASES]); #if defined(CONFIG_SMP) && defined(CONFIG_NO_HZ_COMMON) unsigned int sysctl_timer_migration = 1; @@ -106,15 +216,17 @@ void timers_update_migration(bool update_nohz) unsigned int cpu; /* Avoid the loop, if nothing to update */ - if (this_cpu_read(tvec_bases.migration_enabled) == on) + if (this_cpu_read(timer_bases[BASE_STD].migration_enabled) == on) return; for_each_possible_cpu(cpu) { - per_cpu(tvec_bases.migration_enabled, cpu) = on; + per_cpu(timer_bases[BASE_STD].migration_enabled, cpu) = on; + per_cpu(timer_bases[BASE_DEF].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(timer_bases[BASE_STD].nohz_active, cpu) = true; + per_cpu(timer_bases[BASE_DEF].nohz_active, cpu) = true; per_cpu(hrtimer_bases.nohz_active, cpu) = true; } } @@ -133,20 +245,6 @@ int timer_migration_handler(struct ctl_table *table, int write, mutex_unlock(&mutex); return ret; } - -static inline struct tvec_base *get_target_base(struct tvec_base *base, - int pinned) -{ - if (pinned || !base->migration_enabled) - return this_cpu_ptr(&tvec_bases); - return per_cpu_ptr(&tvec_bases, get_nohz_timer_target()); -} -#else -static inline struct tvec_base *get_target_base(struct tvec_base *base, - int pinned) -{ - return this_cpu_ptr(&tvec_bases); -} #endif static unsigned long round_jiffies_common(unsigned long j, int cpu, @@ -351,101 +449,126 @@ unsigned long round_jiffies_up_relative(unsigned long j) } EXPORT_SYMBOL_GPL(round_jiffies_up_relative); -/** - * set_timer_slack - set the allowed slack for a timer - * @timer: the timer to be modified - * @slack_hz: the amount of time (in jiffies) allowed for rounding - * - * Set the amount of time, in jiffies, that a certain timer has - * in terms of slack. By setting this value, the timer subsystem - * will schedule the actual timer somewhere between - * the time mod_timer() asks for, and that time plus the slack. - * - * By setting the slack to -1, a percentage of the delay is used - * instead. - */ -void set_timer_slack(struct timer_list *timer, int slack_hz) + +static inline unsigned int timer_get_idx(struct timer_list *timer) { - timer->slack = slack_hz; + return (timer->flags & TIMER_ARRAYMASK) >> TIMER_ARRAYSHIFT; } -EXPORT_SYMBOL_GPL(set_timer_slack); -static void -__internal_add_timer(struct tvec_base *base, struct timer_list *timer) +static inline void timer_set_idx(struct timer_list *timer, unsigned int idx) { - unsigned long expires = timer->expires; - unsigned long idx = expires - base->timer_jiffies; - struct hlist_head *vec; + timer->flags = (timer->flags & ~TIMER_ARRAYMASK) | + idx << TIMER_ARRAYSHIFT; +} - if (idx < TVR_SIZE) { - int i = expires & TVR_MASK; - vec = base->tv1.vec + i; - } else if (idx < 1 << (TVR_BITS + TVN_BITS)) { - int i = (expires >> TVR_BITS) & TVN_MASK; - vec = base->tv2.vec + i; - } else if (idx < 1 << (TVR_BITS + 2 * TVN_BITS)) { - int i = (expires >> (TVR_BITS + TVN_BITS)) & TVN_MASK; - vec = base->tv3.vec + i; - } else if (idx < 1 << (TVR_BITS + 3 * TVN_BITS)) { - int i = (expires >> (TVR_BITS + 2 * TVN_BITS)) & TVN_MASK; - vec = base->tv4.vec + i; - } else if ((signed long) idx < 0) { - /* - * Can happen if you add a timer with expires == jiffies, - * or you set a timer to go off in the past - */ - vec = base->tv1.vec + (base->timer_jiffies & TVR_MASK); +/* + * Helper function to calculate the array index for a given expiry + * time. + */ +static inline unsigned calc_index(unsigned expires, unsigned lvl) +{ + expires = (expires + LVL_GRAN(lvl)) >> LVL_SHIFT(lvl); + return LVL_OFFS(lvl) + (expires & LVL_MASK); +} + +static int calc_wheel_index(unsigned long expires, unsigned long clk) +{ + unsigned long delta = expires - clk; + unsigned int idx; + + if (delta < LVL_START(1)) { + idx = calc_index(expires, 0); + } else if (delta < LVL_START(2)) { + idx = calc_index(expires, 1); + } else if (delta < LVL_START(3)) { + idx = calc_index(expires, 2); + } else if (delta < LVL_START(4)) { + idx = calc_index(expires, 3); + } else if (delta < LVL_START(5)) { + idx = calc_index(expires, 4); + } else if (delta < LVL_START(6)) { + idx = calc_index(expires, 5); + } else if (delta < LVL_START(7)) { + idx = calc_index(expires, 6); + } else if (LVL_DEPTH > 8 && delta < LVL_START(8)) { + idx = calc_index(expires, 7); + } else if ((long) delta < 0) { + idx = clk & LVL_MASK; } else { - int i; - /* If the timeout is larger than MAX_TVAL (on 64-bit - * architectures or with CONFIG_BASE_SMALL=1) then we - * use the maximum timeout. + /* + * Force expire obscene large timeouts to expire at the + * capacity limit of the wheel. */ - if (idx > MAX_TVAL) { - idx = MAX_TVAL; - expires = idx + base->timer_jiffies; - } - i = (expires >> (TVR_BITS + 3 * TVN_BITS)) & TVN_MASK; - vec = base->tv5.vec + i; + if (expires >= WHEEL_TIMEOUT_CUTOFF) + expires = WHEEL_TIMEOUT_MAX; + + idx = calc_index(expires, LVL_DEPTH - 1); } + return idx; +} + +/* + * Enqueue the timer into the hash bucket, mark it pending in + * the bitmap and store the index in the timer flags. + */ +static void enqueue_timer(struct timer_base *base, struct timer_list *timer, + unsigned int idx) +{ + hlist_add_head(&timer->entry, base->vectors + idx); + __set_bit(idx, base->pending_map); + timer_set_idx(timer, idx); +} + +static void +__internal_add_timer(struct timer_base *base, struct timer_list *timer) +{ + unsigned int idx; - hlist_add_head(&timer->entry, vec); + idx = calc_wheel_index(timer->expires, base->clk); + enqueue_timer(base, timer, idx); } -static void internal_add_timer(struct tvec_base *base, struct timer_list *timer) +static void +trigger_dyntick_cpu(struct timer_base *base, struct timer_list *timer) { - /* Advance base->jiffies, if the base is empty */ - if (!base->all_timers++) - base->timer_jiffies = jiffies; + if (!IS_ENABLED(CONFIG_NO_HZ_COMMON) || !base->nohz_active) + return; - __internal_add_timer(base, timer); /* - * Update base->active_timers and base->next_timer + * 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 (!(timer->flags & TIMER_DEFERRABLE)) { - if (!base->active_timers++ || - time_before(timer->expires, base->next_timer)) - base->next_timer = timer->expires; + if (timer->flags & TIMER_DEFERRABLE) { + if (tick_nohz_full_cpu(base->cpu)) + wake_up_nohz_cpu(base->cpu); + 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. + * 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->nohz_active) { - if (!(timer->flags & TIMER_DEFERRABLE) || - tick_nohz_full_cpu(base->cpu)) - wake_up_nohz_cpu(base->cpu); - } + 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); +} + +static void +internal_add_timer(struct timer_base *base, struct timer_list *timer) +{ + __internal_add_timer(base, timer); + trigger_dyntick_cpu(base, timer); } #ifdef CONFIG_TIMER_STATS @@ -666,7 +789,6 @@ static void do_init_timer(struct timer_list *timer, unsigned int flags, { timer->entry.pprev = NULL; timer->flags = flags | raw_smp_processor_id(); - timer->slack = -1; #ifdef CONFIG_TIMER_STATS timer->start_site = NULL; timer->start_pid = -1; @@ -706,54 +828,125 @@ static inline void detach_timer(struct timer_list *timer, bool clear_pending) entry->next = LIST_POISON2; } -static inline void -detach_expired_timer(struct timer_list *timer, struct tvec_base *base) -{ - detach_timer(timer, true); - if (!(timer->flags & TIMER_DEFERRABLE)) - base->active_timers--; - base->all_timers--; -} - -static int detach_if_pending(struct timer_list *timer, struct tvec_base *base, +static int detach_if_pending(struct timer_list *timer, struct timer_base *base, bool clear_pending) { + unsigned idx = timer_get_idx(timer); + if (!timer_pending(timer)) return 0; + if (hlist_is_singular_node(&timer->entry, base->vectors + idx)) + __clear_bit(idx, base->pending_map); + detach_timer(timer, clear_pending); - if (!(timer->flags & TIMER_DEFERRABLE)) { - base->active_timers--; - if (timer->expires == base->next_timer) - base->next_timer = base->timer_jiffies; - } - /* If this was the last timer, advance base->jiffies */ - if (!--base->all_timers) - base->timer_jiffies = jiffies; return 1; } +static inline struct timer_base *get_timer_cpu_base(u32 tflags, u32 cpu) +{ + struct timer_base *base = per_cpu_ptr(&timer_bases[BASE_STD], cpu); + + /* + * If the timer is deferrable and nohz is active then we need to use + * the deferrable base. + */ + if (IS_ENABLED(CONFIG_NO_HZ_COMMON) && base->nohz_active && + (tflags & TIMER_DEFERRABLE)) + base = per_cpu_ptr(&timer_bases[BASE_DEF], cpu); + return base; +} + +static inline struct timer_base *get_timer_this_cpu_base(u32 tflags) +{ + struct timer_base *base = this_cpu_ptr(&timer_bases[BASE_STD]); + + /* + * If the timer is deferrable and nohz is active then we need to use + * the deferrable base. + */ + if (IS_ENABLED(CONFIG_NO_HZ_COMMON) && base->nohz_active && + (tflags & TIMER_DEFERRABLE)) + base = this_cpu_ptr(&timer_bases[BASE_DEF]); + return base; +} + +static inline struct timer_base *get_timer_base(u32 tflags) +{ + return get_timer_cpu_base(tflags, tflags & TIMER_CPUMASK); +} + +#ifdef CONFIG_NO_HZ_COMMON +static inline struct timer_base * +__get_target_base(struct timer_base *base, unsigned tflags) +{ +#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()); +#else + return get_timer_this_cpu_base(tflags); +#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(tvec_bases).lock - * means that all timers which are tied to this base via timer->base are - * locked, and the base itself is locked too. + * 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 + * is locked too. * * So __run_timers/migrate_timers can safely modify all timers which could - * be found on ->tvX lists. + * be found in the base->vectors array. * - * When the timer's base is locked and removed from the list, the - * TIMER_MIGRATING flag is set, FIXME + * When a timer is migrating then the TIMER_MIGRATING flag is set and we need + * to wait until the migration is done. */ -static struct tvec_base *lock_timer_base(struct timer_list *timer, - unsigned long *flags) +static struct timer_base *lock_timer_base(struct timer_list *timer, + unsigned long *flags) __acquires(timer->base->lock) { for (;;) { + struct timer_base *base; u32 tf = timer->flags; - struct tvec_base *base; if (!(tf & TIMER_MIGRATING)) { - base = per_cpu_ptr(&tvec_bases, tf & TIMER_CPUMASK); + base = get_timer_base(tf); spin_lock_irqsave(&base->lock, *flags); if (timer->flags == tf) return base; @@ -764,13 +957,41 @@ static struct tvec_base *lock_timer_base(struct timer_list *timer, } static inline int -__mod_timer(struct timer_list *timer, unsigned long expires, - bool pending_only, int pinned) +__mod_timer(struct timer_list *timer, unsigned long expires, bool pending_only) { - struct tvec_base *base, *new_base; - unsigned long flags; + struct timer_base *base, *new_base; + unsigned int idx = UINT_MAX; + unsigned long clk = 0, flags; int ret = 0; + /* + * This is a common optimization triggered by the networking code - if + * the timer is re-modified to have the same timeout or ends up in the + * same array bucket then just return: + */ + if (timer_pending(timer)) { + if (timer->expires == expires) + return 1; + /* + * Take the current timer_jiffies of base, but without holding + * the lock! + */ + base = get_timer_base(timer->flags); + clk = base->clk; + + idx = calc_wheel_index(expires, clk); + + /* + * Retrieve and compare the array index of the pending + * timer. If it matches set the expiry to the new value so a + * subsequent call will exit in the expires check above. + */ + if (idx == timer_get_idx(timer)) { + timer->expires = expires; + return 1; + } + } + timer_stats_timer_set_start_info(timer); BUG_ON(!timer->function); @@ -782,15 +1003,15 @@ __mod_timer(struct timer_list *timer, unsigned long expires, debug_activate(timer, expires); - new_base = get_target_base(base, pinned); + new_base = get_target_base(base, timer->flags); if (base != new_base) { /* - * We are trying to schedule the timer on the local CPU. + * We are trying to schedule the timer on the new base. * However we can't change timer's base while it is running, * otherwise del_timer_sync() can't detect that the timer's - * handler yet has not finished. This also guarantees that - * the timer is serialized wrt itself. + * handler yet has not finished. This also guarantees that the + * timer is serialized wrt itself. */ if (likely(base->running_timer != timer)) { /* See the comment in lock_timer_base() */ @@ -805,7 +1026,18 @@ __mod_timer(struct timer_list *timer, unsigned long expires, } timer->expires = expires; - internal_add_timer(base, timer); + /* + * If 'idx' was calculated above and the base time did not advance + * between calculating 'idx' and taking the lock, only enqueue_timer() + * and trigger_dyntick_cpu() is required. Otherwise we need to + * (re)calculate the wheel index via internal_add_timer(). + */ + if (idx != UINT_MAX && clk == base->clk) { + enqueue_timer(base, timer, idx); + trigger_dyntick_cpu(base, timer); + } else { + internal_add_timer(base, timer); + } out_unlock: spin_unlock_irqrestore(&base->lock, flags); @@ -825,49 +1057,10 @@ out_unlock: */ int mod_timer_pending(struct timer_list *timer, unsigned long expires) { - return __mod_timer(timer, expires, true, TIMER_NOT_PINNED); + return __mod_timer(timer, expires, true); } EXPORT_SYMBOL(mod_timer_pending); -/* - * Decide where to put the timer while taking the slack into account - * - * Algorithm: - * 1) calculate the maximum (absolute) time - * 2) calculate the highest bit where the expires and new max are different - * 3) use this bit to make a mask - * 4) use the bitmask to round down the maximum time, so that all last - * bits are zeros - */ -static inline -unsigned long apply_slack(struct timer_list *timer, unsigned long expires) -{ - unsigned long expires_limit, mask; - int bit; - - if (timer->slack >= 0) { - expires_limit = expires + timer->slack; - } else { - long delta = expires - jiffies; - - if (delta < 256) - return expires; - - expires_limit = expires + delta / 256; - } - mask = expires ^ expires_limit; - if (mask == 0) - return expires; - - bit = __fls(mask); - - mask = (1UL << bit) - 1; - - expires_limit = expires_limit & ~(mask); - - return expires_limit; -} - /** * mod_timer - modify a timer's timeout * @timer: the timer to be modified @@ -890,49 +1083,11 @@ unsigned long apply_slack(struct timer_list *timer, unsigned long expires) */ int mod_timer(struct timer_list *timer, unsigned long expires) { - expires = apply_slack(timer, expires); - - /* - * This is a common optimization triggered by the - * networking code - if the timer is re-modified - * to be the same thing then just return: - */ - if (timer_pending(timer) && timer->expires == expires) - return 1; - - return __mod_timer(timer, expires, false, TIMER_NOT_PINNED); + return __mod_timer(timer, expires, false); } EXPORT_SYMBOL(mod_timer); /** - * mod_timer_pinned - modify a timer's timeout - * @timer: the timer to be modified - * @expires: new timeout in jiffies - * - * mod_timer_pinned() is a way to update the expire field of an - * active timer (if the timer is inactive it will be activated) - * and to ensure that the timer is scheduled on the current CPU. - * - * Note that this does not prevent the timer from being migrated - * when the current CPU goes offline. If this is a problem for - * you, use CPU-hotplug notifiers to handle it correctly, for - * example, cancelling the timer when the corresponding CPU goes - * offline. - * - * mod_timer_pinned(timer, expires) is equivalent to: - * - * del_timer(timer); timer->expires = expires; add_timer(timer); - */ -int mod_timer_pinned(struct timer_list *timer, unsigned long expires) -{ - if (timer->expires == expires && timer_pending(timer)) - return 1; - - return __mod_timer(timer, expires, false, TIMER_PINNED); -} -EXPORT_SYMBOL(mod_timer_pinned); - -/** * add_timer - start a timer * @timer: the timer to be added * @@ -962,13 +1117,14 @@ EXPORT_SYMBOL(add_timer); */ void add_timer_on(struct timer_list *timer, int cpu) { - struct tvec_base *new_base = per_cpu_ptr(&tvec_bases, cpu); - struct tvec_base *base; + struct timer_base *new_base, *base; unsigned long flags; timer_stats_timer_set_start_info(timer); BUG_ON(timer_pending(timer) || !timer->function); + new_base = get_timer_cpu_base(timer->flags, cpu); + /* * If @timer was on a different CPU, it should be migrated with the * old base locked to prevent other operations proceeding with the @@ -1004,7 +1160,7 @@ EXPORT_SYMBOL_GPL(add_timer_on); */ int del_timer(struct timer_list *timer) { - struct tvec_base *base; + struct timer_base *base; unsigned long flags; int ret = 0; @@ -1030,7 +1186,7 @@ EXPORT_SYMBOL(del_timer); */ int try_to_del_timer_sync(struct timer_list *timer) { - struct tvec_base *base; + struct timer_base *base; unsigned long flags; int ret = -1; @@ -1114,27 +1270,6 @@ int del_timer_sync(struct timer_list *timer) EXPORT_SYMBOL(del_timer_sync); #endif -static int cascade(struct tvec_base *base, struct tvec *tv, int index) -{ - /* cascade all the timers from tv up one level */ - struct timer_list *timer; - struct hlist_node *tmp; - struct hlist_head tv_list; - - hlist_move_list(tv->vec + index, &tv_list); - - /* - * We are removing _all_ timers from the list, so we - * don't have to detach them individually. - */ - hlist_for_each_entry_safe(timer, tmp, &tv_list, entry) { - /* No accounting, while moving them */ - __internal_add_timer(base, timer); - } - - return index; -} - static void call_timer_fn(struct timer_list *timer, void (*fn)(unsigned long), unsigned long data) { @@ -1178,147 +1313,141 @@ static void call_timer_fn(struct timer_list *timer, void (*fn)(unsigned long), } } -#define INDEX(N) ((base->timer_jiffies >> (TVR_BITS + (N) * TVN_BITS)) & TVN_MASK) - -/** - * __run_timers - run all expired timers (if any) on this CPU. - * @base: the timer vector to be processed. - * - * This function cascades all vectors and executes all expired timer - * vectors. - */ -static inline void __run_timers(struct tvec_base *base) +static void expire_timers(struct timer_base *base, struct hlist_head *head) { - struct timer_list *timer; + while (!hlist_empty(head)) { + struct timer_list *timer; + void (*fn)(unsigned long); + unsigned long data; - spin_lock_irq(&base->lock); + timer = hlist_entry(head->first, struct timer_list, entry); + timer_stats_account_timer(timer); - while (time_after_eq(jiffies, base->timer_jiffies)) { - struct hlist_head work_list; - struct hlist_head *head = &work_list; - int index; + base->running_timer = timer; + detach_timer(timer, true); - if (!base->all_timers) { - base->timer_jiffies = jiffies; - break; + fn = timer->function; + data = timer->data; + + if (timer->flags & TIMER_IRQSAFE) { + spin_unlock(&base->lock); + call_timer_fn(timer, fn, data); + spin_lock(&base->lock); + } else { + spin_unlock_irq(&base->lock); + call_timer_fn(timer, fn, data); + spin_lock_irq(&base->lock); } + } +} - index = base->timer_jiffies & TVR_MASK; +static int __collect_expired_timers(struct timer_base *base, + struct hlist_head *heads) +{ + unsigned long clk = base->clk; + struct hlist_head *vec; + int i, levels = 0; + unsigned int idx; - /* - * Cascade timers: - */ - if (!index && - (!cascade(base, &base->tv2, INDEX(0))) && - (!cascade(base, &base->tv3, INDEX(1))) && - !cascade(base, &base->tv4, INDEX(2))) - cascade(base, &base->tv5, INDEX(3)); - ++base->timer_jiffies; - hlist_move_list(base->tv1.vec + index, head); - while (!hlist_empty(head)) { - void (*fn)(unsigned long); - unsigned long data; - bool irqsafe; - - timer = hlist_entry(head->first, struct timer_list, entry); - fn = timer->function; - data = timer->data; - irqsafe = timer->flags & TIMER_IRQSAFE; - - timer_stats_account_timer(timer); - - base->running_timer = timer; - detach_expired_timer(timer, base); - - if (irqsafe) { - spin_unlock(&base->lock); - call_timer_fn(timer, fn, data); - spin_lock(&base->lock); - } else { - spin_unlock_irq(&base->lock); - call_timer_fn(timer, fn, data); - spin_lock_irq(&base->lock); - } + for (i = 0; i < LVL_DEPTH; i++) { + idx = (clk & LVL_MASK) + i * LVL_SIZE; + + if (__test_and_clear_bit(idx, base->pending_map)) { + vec = base->vectors + idx; + hlist_move_list(vec, heads++); + levels++; } + /* Is it time to look at the next level? */ + if (clk & LVL_CLK_MASK) + break; + /* Shift clock for the next level granularity */ + clk >>= LVL_CLK_SHIFT; } - base->running_timer = NULL; - spin_unlock_irq(&base->lock); + return levels; } #ifdef CONFIG_NO_HZ_COMMON /* - * Find out when the next timer event is due to happen. This - * is used on S/390 to stop all activity when a CPU is idle. - * This function needs to be called with interrupts disabled. + * Find the next pending bucket of a level. Search from level start (@offset) + * + @clk upwards and if nothing there, search from start of the level + * (@offset) up to @offset + clk. + */ +static int next_pending_bucket(struct timer_base *base, unsigned offset, + unsigned clk) +{ + unsigned pos, start = offset + clk; + unsigned end = offset + LVL_SIZE; + + pos = find_next_bit(base->pending_map, end, start); + if (pos < end) + return pos - start; + + pos = find_next_bit(base->pending_map, start, offset); + return pos < start ? pos + LVL_SIZE - start : -1; +} + +/* + * Search the first expiring timer in the various clock levels. Caller must + * hold base->lock. */ -static unsigned long __next_timer_interrupt(struct tvec_base *base) -{ - unsigned long timer_jiffies = base->timer_jiffies; - unsigned long expires = timer_jiffies + NEXT_TIMER_MAX_DELTA; - int index, slot, array, found = 0; - struct timer_list *nte; - struct tvec *varray[4]; - - /* Look for timer events in tv1. */ - index = slot = timer_jiffies & TVR_MASK; - do { - hlist_for_each_entry(nte, base->tv1.vec + slot, entry) { - if (nte->flags & TIMER_DEFERRABLE) - continue; - - found = 1; - expires = nte->expires; - /* Look at the cascade bucket(s)? */ - if (!index || slot < index) - goto cascade; - return expires; +static unsigned long __next_timer_interrupt(struct timer_base *base) +{ + unsigned long clk, next, adj; + unsigned lvl, offset = 0; + + next = base->clk + NEXT_TIMER_MAX_DELTA; + clk = base->clk; + for (lvl = 0; lvl < LVL_DEPTH; lvl++, offset += LVL_SIZE) { + int pos = next_pending_bucket(base, offset, clk & LVL_MASK); + + if (pos >= 0) { + unsigned long tmp = clk + (unsigned long) pos; + + tmp <<= LVL_SHIFT(lvl); + if (time_before(tmp, next)) + next = tmp; } - slot = (slot + 1) & TVR_MASK; - } while (slot != index); - -cascade: - /* Calculate the next cascade event */ - if (index) - timer_jiffies += TVR_SIZE - index; - timer_jiffies >>= TVR_BITS; - - /* Check tv2-tv5. */ - varray[0] = &base->tv2; - varray[1] = &base->tv3; - varray[2] = &base->tv4; - varray[3] = &base->tv5; - - for (array = 0; array < 4; array++) { - struct tvec *varp = varray[array]; - - index = slot = timer_jiffies & TVN_MASK; - do { - hlist_for_each_entry(nte, varp->vec + slot, entry) { - if (nte->flags & TIMER_DEFERRABLE) - continue; - - found = 1; - if (time_before(nte->expires, expires)) - expires = nte->expires; - } - /* - * Do we still search for the first timer or are - * we looking up the cascade buckets ? - */ - if (found) { - /* Look at the cascade bucket(s)? */ - if (!index || slot < index) - break; - return expires; - } - slot = (slot + 1) & TVN_MASK; - } while (slot != index); - - if (index) - timer_jiffies += TVN_SIZE - index; - timer_jiffies >>= TVN_BITS; + /* + * Clock for the next level. If the current level clock lower + * bits are zero, we look at the next level as is. If not we + * need to advance it by one because that's going to be the + * next expiring bucket in that level. base->clk is the next + * expiring jiffie. So in case of: + * + * LVL5 LVL4 LVL3 LVL2 LVL1 LVL0 + * 0 0 0 0 0 0 + * + * we have to look at all levels @index 0. With + * + * LVL5 LVL4 LVL3 LVL2 LVL1 LVL0 + * 0 0 0 0 0 2 + * + * LVL0 has the next expiring bucket @index 2. The upper + * levels have the next expiring bucket @index 1. + * + * In case that the propagation wraps the next level the same + * rules apply: + * + * LVL5 LVL4 LVL3 LVL2 LVL1 LVL0 + * 0 0 0 0 F 2 + * + * So after looking at LVL0 we get: + * + * LVL5 LVL4 LVL3 LVL2 LVL1 + * 0 0 0 1 0 + * + * So no propagation from LVL1 to LVL2 because that happened + * with the add already, but then we need to propagate further + * from LVL2 to LVL3. + * + * So the simple check whether the lower bits of the current + * level are 0 or not is sufficient for all cases. + */ + adj = clk & LVL_CLK_MASK ? 1 : 0; + clk >>= LVL_CLK_SHIFT; + clk += adj; } - return expires; + return next; } /* @@ -1364,9 +1493,10 @@ static u64 cmp_next_hrtimer_event(u64 basem, u64 expires) */ u64 get_next_timer_interrupt(unsigned long basej, u64 basem) { - struct tvec_base *base = this_cpu_ptr(&tvec_bases); + struct timer_base *base = this_cpu_ptr(&timer_bases[BASE_STD]); u64 expires = KTIME_MAX; unsigned long nextevt; + bool is_max_delta; /* * Pretend that there is no timer pending if the cpu is offline. @@ -1376,19 +1506,82 @@ u64 get_next_timer_interrupt(unsigned long basej, u64 basem) return expires; spin_lock(&base->lock); - if (base->active_timers) { - if (time_before_eq(base->next_timer, base->timer_jiffies)) - base->next_timer = __next_timer_interrupt(base); - nextevt = base->next_timer; - if (time_before_eq(nextevt, basej)) - expires = basem; - else + nextevt = __next_timer_interrupt(base); + is_max_delta = (nextevt == base->clk + NEXT_TIMER_MAX_DELTA); + 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)) { + expires = basem; + base->is_idle = false; + } else { + if (!is_max_delta) 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) +{ + /* + * NOHZ optimization. After a long idle sleep we need to forward the + * base to current jiffies. Avoid a loop by searching the bitfield for + * the next expiring timer. + */ + if ((long)(jiffies - base->clk) > 2) { + unsigned long next = __next_timer_interrupt(base); + + /* + * If the next timer is ahead of time forward to current + * jiffies, otherwise forward to the next expiry time: + */ + if (time_after(next, jiffies)) { + /* The call site will increment clock! */ + base->clk = jiffies - 1; + return 0; + } + base->clk = next; + } + return __collect_expired_timers(base, heads); +} +#else +static inline int collect_expired_timers(struct timer_base *base, + struct hlist_head *heads) +{ + return __collect_expired_timers(base, heads); +} #endif /* @@ -1411,15 +1604,42 @@ void update_process_times(int user_tick) run_posix_cpu_timers(p); } +/** + * __run_timers - run all expired timers (if any) on this CPU. + * @base: the timer vector to be processed. + */ +static inline void __run_timers(struct timer_base *base) +{ + struct hlist_head heads[LVL_DEPTH]; + int levels; + + if (!time_after_eq(jiffies, base->clk)) + return; + + spin_lock_irq(&base->lock); + + while (time_after_eq(jiffies, base->clk)) { + + levels = collect_expired_timers(base, heads); + base->clk++; + + while (levels--) + expire_timers(base, heads + levels); + } + base->running_timer = NULL; + spin_unlock_irq(&base->lock); +} + /* * This function runs timers and the timer-tq in bottom half context. */ static void run_timer_softirq(struct softirq_action *h) { - struct tvec_base *base = this_cpu_ptr(&tvec_bases); + struct timer_base *base = this_cpu_ptr(&timer_bases[BASE_STD]); - if (time_after_eq(jiffies, base->timer_jiffies)) - __run_timers(base); + __run_timers(base); + if (IS_ENABLED(CONFIG_NO_HZ_COMMON) && base->nohz_active) + __run_timers(this_cpu_ptr(&timer_bases[BASE_DEF])); } /* @@ -1427,7 +1647,18 @@ static void run_timer_softirq(struct softirq_action *h) */ void run_local_timers(void) { + struct timer_base *base = this_cpu_ptr(&timer_bases[BASE_STD]); + hrtimer_run_queues(); + /* Raise the softirq only if required. */ + if (time_before(jiffies, base->clk)) { + if (!IS_ENABLED(CONFIG_NO_HZ_COMMON) || !base->nohz_active) + return; + /* CPU is awake, so check the deferrable base. */ + base++; + if (time_before(jiffies, base->clk)) + return; + } raise_softirq(TIMER_SOFTIRQ); } @@ -1512,7 +1743,7 @@ signed long __sched schedule_timeout(signed long timeout) expire = timeout + jiffies; setup_timer_on_stack(&timer, process_timeout, (unsigned long)current); - __mod_timer(&timer, expire, false, TIMER_NOT_PINNED); + __mod_timer(&timer, expire, false); schedule(); del_singleshot_timer_sync(&timer); @@ -1563,87 +1794,62 @@ signed long __sched schedule_timeout_idle(signed long timeout) EXPORT_SYMBOL(schedule_timeout_idle); #ifdef CONFIG_HOTPLUG_CPU -static void migrate_timer_list(struct tvec_base *new_base, struct hlist_head *head) +static void migrate_timer_list(struct timer_base *new_base, struct hlist_head *head) { struct timer_list *timer; int cpu = new_base->cpu; while (!hlist_empty(head)) { timer = hlist_entry(head->first, struct timer_list, entry); - /* We ignore the accounting on the dying cpu */ detach_timer(timer, false); timer->flags = (timer->flags & ~TIMER_BASEMASK) | cpu; internal_add_timer(new_base, timer); } } -static void migrate_timers(int cpu) +int timers_dead_cpu(unsigned int cpu) { - struct tvec_base *old_base; - struct tvec_base *new_base; - int i; + struct timer_base *old_base; + struct timer_base *new_base; + int b, i; BUG_ON(cpu_online(cpu)); - old_base = per_cpu_ptr(&tvec_bases, cpu); - new_base = get_cpu_ptr(&tvec_bases); - /* - * The caller is globally serialized and nobody else - * takes two locks at once, deadlock is not possible. - */ - spin_lock_irq(&new_base->lock); - spin_lock_nested(&old_base->lock, SINGLE_DEPTH_NESTING); - - BUG_ON(old_base->running_timer); - - for (i = 0; i < TVR_SIZE; i++) - migrate_timer_list(new_base, old_base->tv1.vec + i); - for (i = 0; i < TVN_SIZE; i++) { - migrate_timer_list(new_base, old_base->tv2.vec + i); - migrate_timer_list(new_base, old_base->tv3.vec + i); - migrate_timer_list(new_base, old_base->tv4.vec + i); - migrate_timer_list(new_base, old_base->tv5.vec + i); - } - old_base->active_timers = 0; - old_base->all_timers = 0; + for (b = 0; b < NR_BASES; b++) { + old_base = per_cpu_ptr(&timer_bases[b], cpu); + new_base = get_cpu_ptr(&timer_bases[b]); + /* + * The caller is globally serialized and nobody else + * takes two locks at once, deadlock is not possible. + */ + spin_lock_irq(&new_base->lock); + spin_lock_nested(&old_base->lock, SINGLE_DEPTH_NESTING); - spin_unlock(&old_base->lock); - spin_unlock_irq(&new_base->lock); - put_cpu_ptr(&tvec_bases); -} + BUG_ON(old_base->running_timer); -static int timer_cpu_notify(struct notifier_block *self, - unsigned long action, void *hcpu) -{ - switch (action) { - case CPU_DEAD: - case CPU_DEAD_FROZEN: - migrate_timers((long)hcpu); - break; - default: - break; - } + for (i = 0; i < WHEEL_SIZE; i++) + migrate_timer_list(new_base, old_base->vectors + i); - return NOTIFY_OK; + spin_unlock(&old_base->lock); + spin_unlock_irq(&new_base->lock); + put_cpu_ptr(&timer_bases); + } + return 0; } -static inline void timer_register_cpu_notifier(void) -{ - cpu_notifier(timer_cpu_notify, 0); -} -#else -static inline void timer_register_cpu_notifier(void) { } #endif /* CONFIG_HOTPLUG_CPU */ static void __init init_timer_cpu(int cpu) { - struct tvec_base *base = per_cpu_ptr(&tvec_bases, cpu); - - base->cpu = cpu; - spin_lock_init(&base->lock); + struct timer_base *base; + int i; - base->timer_jiffies = jiffies; - base->next_timer = base->timer_jiffies; + for (i = 0; i < NR_BASES; i++) { + base = per_cpu_ptr(&timer_bases[i], cpu); + base->cpu = cpu; + spin_lock_init(&base->lock); + base->clk = jiffies; + } } static void __init init_timer_cpus(void) @@ -1658,7 +1864,6 @@ void __init init_timers(void) { init_timer_cpus(); init_timer_stats(); - timer_register_cpu_notifier(); open_softirq(TIMER_SOFTIRQ, run_timer_softirq); } @@ -1702,9 +1907,15 @@ static void __sched do_usleep_range(unsigned long min, unsigned long max) } /** - * usleep_range - Drop in replacement for udelay where wakeup is flexible + * usleep_range - Sleep for an approximate time * @min: Minimum time in usecs to sleep * @max: Maximum time in usecs to sleep + * + * In non-atomic context where the exact wakeup time is flexible, use + * usleep_range() instead of udelay(). The sleep improves responsiveness + * by avoiding the CPU-hogging busy-wait of udelay(), and the range reduces + * power usage by allowing hrtimers to take advantage of an already- + * scheduled interrupt instead of scheduling a new one just for this sleep. */ void __sched usleep_range(unsigned long min, unsigned long max) { |