diff options
Diffstat (limited to 'kernel/sched_fair.c')
| -rw-r--r-- | kernel/sched_fair.c | 216 |
1 files changed, 180 insertions, 36 deletions
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c index fedbb51..67c67a8 100644 --- a/kernel/sched_fair.c +++ b/kernel/sched_fair.c @@ -15,34 +15,50 @@ * * Scaled math optimizations by Thomas Gleixner * Copyright (C) 2007, Thomas Gleixner <tglx@linutronix.de> + * + * Adaptive scheduling granularity, math enhancements by Peter Zijlstra + * Copyright (C) 2007 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com> */ /* - * Preemption granularity: - * (default: 2 msec, units: nanoseconds) + * Targeted preemption latency for CPU-bound tasks: + * (default: 20ms, units: nanoseconds) * - * NOTE: this granularity value is not the same as the concept of - * 'timeslice length' - timeslices in CFS will typically be somewhat - * larger than this value. (to see the precise effective timeslice - * length of your workload, run vmstat and monitor the context-switches - * field) + * NOTE: this latency value is not the same as the concept of + * 'timeslice length' - timeslices in CFS are of variable length. + * (to see the precise effective timeslice length of your workload, + * run vmstat and monitor the context-switches field) * * On SMP systems the value of this is multiplied by the log2 of the * number of CPUs. (i.e. factor 2x on 2-way systems, 3x on 4-way * systems, 4x on 8-way systems, 5x on 16-way systems, etc.) + * Targeted preemption latency for CPU-bound tasks: + */ +unsigned int sysctl_sched_latency __read_mostly = 20000000ULL; + +/* + * Minimal preemption granularity for CPU-bound tasks: + * (default: 2 msec, units: nanoseconds) */ -unsigned int sysctl_sched_granularity __read_mostly = 2000000000ULL/HZ; +unsigned int sysctl_sched_min_granularity __read_mostly = 2000000ULL; + +/* + * sys_sched_yield() compat mode + * + * This option switches the agressive yield implementation of the + * old scheduler back on. + */ +unsigned int __read_mostly sysctl_sched_compat_yield; /* * SCHED_BATCH wake-up granularity. - * (default: 10 msec, units: nanoseconds) + * (default: 25 msec, units: nanoseconds) * * This option delays the preemption effects of decoupled workloads * and reduces their over-scheduling. Synchronous workloads will still * have immediate wakeup/sleep latencies. */ -unsigned int sysctl_sched_batch_wakeup_granularity __read_mostly = - 10000000000ULL/HZ; +unsigned int sysctl_sched_batch_wakeup_granularity __read_mostly = 25000000UL; /* * SCHED_OTHER wake-up granularity. @@ -52,12 +68,12 @@ unsigned int sysctl_sched_batch_wakeup_granularity __read_mostly = * and reduces their over-scheduling. Synchronous workloads will still * have immediate wakeup/sleep latencies. */ -unsigned int sysctl_sched_wakeup_granularity __read_mostly = 1000000000ULL/HZ; +unsigned int sysctl_sched_wakeup_granularity __read_mostly = 1000000UL; unsigned int sysctl_sched_stat_granularity __read_mostly; /* - * Initialized in sched_init_granularity(): + * Initialized in sched_init_granularity() [to 5 times the base granularity]: */ unsigned int sysctl_sched_runtime_limit __read_mostly; @@ -186,6 +202,8 @@ __enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se) update_load_add(&cfs_rq->load, se->load.weight); cfs_rq->nr_running++; se->on_rq = 1; + + schedstat_add(cfs_rq, wait_runtime, se->wait_runtime); } static inline void @@ -197,6 +215,8 @@ __dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se) update_load_sub(&cfs_rq->load, se->load.weight); cfs_rq->nr_running--; se->on_rq = 0; + + schedstat_add(cfs_rq, wait_runtime, -se->wait_runtime); } static inline struct rb_node *first_fair(struct cfs_rq *cfs_rq) @@ -214,6 +234,49 @@ static struct sched_entity *__pick_next_entity(struct cfs_rq *cfs_rq) */ /* + * Calculate the preemption granularity needed to schedule every + * runnable task once per sysctl_sched_latency amount of time. + * (down to a sensible low limit on granularity) + * + * For example, if there are 2 tasks running and latency is 10 msecs, + * we switch tasks every 5 msecs. If we have 3 tasks running, we have + * to switch tasks every 3.33 msecs to get a 10 msecs observed latency + * for each task. We do finer and finer scheduling up to until we + * reach the minimum granularity value. + * + * To achieve this we use the following dynamic-granularity rule: + * + * gran = lat/nr - lat/nr/nr + * + * This comes out of the following equations: + * + * kA1 + gran = kB1 + * kB2 + gran = kA2 + * kA2 = kA1 + * kB2 = kB1 - d + d/nr + * lat = d * nr + * + * Where 'k' is key, 'A' is task A (waiting), 'B' is task B (running), + * '1' is start of time, '2' is end of time, 'd' is delay between + * 1 and 2 (during which task B was running), 'nr' is number of tasks + * running, 'lat' is the the period of each task. ('lat' is the + * sched_latency that we aim for.) + */ +static long +sched_granularity(struct cfs_rq *cfs_rq) +{ + unsigned int gran = sysctl_sched_latency; + unsigned int nr = cfs_rq->nr_running; + + if (nr > 1) { + gran = gran/nr - gran/nr/nr; + gran = max(gran, sysctl_sched_min_granularity); + } + + return gran; +} + +/* * We rescale the rescheduling granularity of tasks according to their * nice level, but only linearly, not exponentially: */ @@ -240,7 +303,7 @@ niced_granularity(struct sched_entity *curr, unsigned long granularity) /* * It will always fit into 'long': */ - return (long) (tmp >> WMULT_SHIFT); + return (long) (tmp >> (WMULT_SHIFT-NICE_0_SHIFT)); } static inline void @@ -303,10 +366,10 @@ __update_curr(struct cfs_rq *cfs_rq, struct sched_entity *curr) delta_fair = calc_delta_fair(delta_exec, lw); delta_mine = calc_delta_mine(delta_exec, curr->load.weight, lw); - if (cfs_rq->sleeper_bonus > sysctl_sched_granularity) { - delta = min(cfs_rq->sleeper_bonus, (u64)delta_exec); - delta = calc_delta_mine(delta, curr->load.weight, lw); - delta = min((u64)delta, cfs_rq->sleeper_bonus); + if (cfs_rq->sleeper_bonus > sysctl_sched_min_granularity) { + delta = min((u64)delta_mine, cfs_rq->sleeper_bonus); + delta = min(delta, (unsigned long)( + (long)sysctl_sched_runtime_limit - curr->wait_runtime)); cfs_rq->sleeper_bonus -= delta; delta_mine -= delta; } @@ -438,6 +501,9 @@ update_stats_wait_end(struct cfs_rq *cfs_rq, struct sched_entity *se) { unsigned long delta_fair; + if (unlikely(!se->wait_start_fair)) + return; + delta_fair = (unsigned long)min((u64)(2*sysctl_sched_runtime_limit), (u64)(cfs_rq->fair_clock - se->wait_start_fair)); @@ -494,6 +560,13 @@ static void __enqueue_sleeper(struct cfs_rq *cfs_rq, struct sched_entity *se) unsigned long load = cfs_rq->load.weight, delta_fair; long prev_runtime; + /* + * Do not boost sleepers if there's too much bonus 'in flight' + * already: + */ + if (unlikely(cfs_rq->sleeper_bonus > sysctl_sched_runtime_limit)) + return; + if (sysctl_sched_features & SCHED_FEAT_SLEEPER_LOAD_AVG) load = rq_of(cfs_rq)->cpu_load[2]; @@ -519,10 +592,6 @@ static void __enqueue_sleeper(struct cfs_rq *cfs_rq, struct sched_entity *se) * Track the amount of bonus we've given to sleepers: */ cfs_rq->sleeper_bonus += delta_fair; - if (unlikely(cfs_rq->sleeper_bonus > sysctl_sched_runtime_limit)) - cfs_rq->sleeper_bonus = sysctl_sched_runtime_limit; - - schedstat_add(cfs_rq, wait_runtime, se->wait_runtime); } static void enqueue_sleeper(struct cfs_rq *cfs_rq, struct sched_entity *se) @@ -570,6 +639,16 @@ static void enqueue_sleeper(struct cfs_rq *cfs_rq, struct sched_entity *se) se->block_start = 0; se->sum_sleep_runtime += delta; + + /* + * Blocking time is in units of nanosecs, so shift by 20 to + * get a milliseconds-range estimation of the amount of + * time that the task spent sleeping: + */ + if (unlikely(prof_on == SLEEP_PROFILING)) { + profile_hits(SLEEP_PROFILING, (void *)get_wchan(tsk), + delta >> 20); + } } #endif } @@ -604,7 +683,6 @@ dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int sleep) if (tsk->state & TASK_UNINTERRUPTIBLE) se->block_start = rq_of(cfs_rq)->clock; } - cfs_rq->wait_runtime -= se->wait_runtime; #endif } __dequeue_entity(cfs_rq, se); @@ -618,11 +696,31 @@ __check_preempt_curr_fair(struct cfs_rq *cfs_rq, struct sched_entity *se, struct sched_entity *curr, unsigned long granularity) { s64 __delta = curr->fair_key - se->fair_key; + unsigned long ideal_runtime, delta_exec; + + /* + * ideal_runtime is compared against sum_exec_runtime, which is + * walltime, hence do not scale. + */ + ideal_runtime = max(sysctl_sched_latency / cfs_rq->nr_running, + (unsigned long)sysctl_sched_min_granularity); + + /* + * If we executed more than what the latency constraint suggests, + * reduce the rescheduling granularity. This way the total latency + * of how much a task is not scheduled converges to + * sysctl_sched_latency: + */ + delta_exec = curr->sum_exec_runtime - curr->prev_sum_exec_runtime; + if (delta_exec > ideal_runtime) + granularity = 0; /* * Take scheduling granularity into account - do not * preempt the current task unless the best task has * a larger than sched_granularity fairness advantage: + * + * scale granularity as key space is in fair_clock. */ if (__delta > niced_granularity(curr, granularity)) resched_task(rq_of(cfs_rq)->curr); @@ -641,6 +739,7 @@ set_next_entity(struct cfs_rq *cfs_rq, struct sched_entity *se) update_stats_wait_end(cfs_rq, se); update_stats_curr_start(cfs_rq, se); set_cfs_rq_curr(cfs_rq, se); + se->prev_sum_exec_runtime = se->sum_exec_runtime; } static struct sched_entity *pick_next_entity(struct cfs_rq *cfs_rq) @@ -686,7 +785,8 @@ static void entity_tick(struct cfs_rq *cfs_rq, struct sched_entity *curr) if (next == curr) return; - __check_preempt_curr_fair(cfs_rq, next, curr, sysctl_sched_granularity); + __check_preempt_curr_fair(cfs_rq, next, curr, + sched_granularity(cfs_rq)); } /************************************************** @@ -815,19 +915,62 @@ static void dequeue_task_fair(struct rq *rq, struct task_struct *p, int sleep) } /* - * sched_yield() support is very simple - we dequeue and enqueue + * sched_yield() support is very simple - we dequeue and enqueue. + * + * If compat_yield is turned on then we requeue to the end of the tree. */ static void yield_task_fair(struct rq *rq, struct task_struct *p) { struct cfs_rq *cfs_rq = task_cfs_rq(p); + struct rb_node **link = &cfs_rq->tasks_timeline.rb_node; + struct sched_entity *rightmost, *se = &p->se; + struct rb_node *parent; - __update_rq_clock(rq); /* - * Dequeue and enqueue the task to update its - * position within the tree: + * Are we the only task in the tree? + */ + if (unlikely(cfs_rq->nr_running == 1)) + return; + + if (likely(!sysctl_sched_compat_yield)) { + __update_rq_clock(rq); + /* + * Dequeue and enqueue the task to update its + * position within the tree: + */ + dequeue_entity(cfs_rq, &p->se, 0); + enqueue_entity(cfs_rq, &p->se, 0); + + return; + } + /* + * Find the rightmost entry in the rbtree: + */ + do { + parent = *link; + link = &parent->rb_right; + } while (*link); + + rightmost = rb_entry(parent, struct sched_entity, run_node); + /* + * Already in the rightmost position? + */ + if (unlikely(rightmost == se)) + return; + + /* + * Minimally necessary key value to be last in the tree: */ - dequeue_entity(cfs_rq, &p->se, 0); - enqueue_entity(cfs_rq, &p->se, 0); + se->fair_key = rightmost->fair_key + 1; + + if (cfs_rq->rb_leftmost == &se->run_node) + cfs_rq->rb_leftmost = rb_next(&se->run_node); + /* + * Relink the task to the rightmost position: + */ + rb_erase(&se->run_node, &cfs_rq->tasks_timeline); + rb_link_node(&se->run_node, parent, link); + rb_insert_color(&se->run_node, &cfs_rq->tasks_timeline); } /* @@ -1020,31 +1163,32 @@ static void task_tick_fair(struct rq *rq, struct task_struct *curr) static void task_new_fair(struct rq *rq, struct task_struct *p) { struct cfs_rq *cfs_rq = task_cfs_rq(p); - struct sched_entity *se = &p->se; + struct sched_entity *se = &p->se, *curr = cfs_rq_curr(cfs_rq); sched_info_queued(p); + update_curr(cfs_rq); update_stats_enqueue(cfs_rq, se); /* * Child runs first: we let it run before the parent * until it reschedules once. We set up the key so that * it will preempt the parent: */ - p->se.fair_key = current->se.fair_key - - niced_granularity(&rq->curr->se, sysctl_sched_granularity) - 1; + se->fair_key = curr->fair_key - + niced_granularity(curr, sched_granularity(cfs_rq)) - 1; /* * The first wait is dominated by the child-runs-first logic, * so do not credit it with that waiting time yet: */ if (sysctl_sched_features & SCHED_FEAT_SKIP_INITIAL) - p->se.wait_start_fair = 0; + se->wait_start_fair = 0; /* * The statistical average of wait_runtime is about * -granularity/2, so initialize the task with that: */ if (sysctl_sched_features & SCHED_FEAT_START_DEBIT) - p->se.wait_runtime = -(sysctl_sched_granularity / 2); + se->wait_runtime = -(sched_granularity(cfs_rq) / 2); __enqueue_entity(cfs_rq, se); } @@ -1057,7 +1201,7 @@ static void task_new_fair(struct rq *rq, struct task_struct *p) */ static void set_curr_task_fair(struct rq *rq) { - struct sched_entity *se = &rq->curr.se; + struct sched_entity *se = &rq->curr->se; for_each_sched_entity(se) set_next_entity(cfs_rq_of(se), se); |