From 9ee474f55664ff63111c843099d365e7ecffb56f Mon Sep 17 00:00:00 2001 From: Paul Turner Date: Thu, 4 Oct 2012 13:18:30 +0200 Subject: [PATCH] sched: Maintain the load contribution of blocked entities We are currently maintaining: runnable_load(cfs_rq) = \Sum task_load(t) For all running children t of cfs_rq. While this can be naturally updated for tasks in a runnable state (as they are scheduled); this does not account for the load contributed by blocked task entities. This can be solved by introducing a separate accounting for blocked load: blocked_load(cfs_rq) = \Sum runnable(b) * weight(b) Obviously we do not want to iterate over all blocked entities to account for their decay, we instead observe that: runnable_load(t) = \Sum p_i*y^i and that to account for an additional idle period we only need to compute: y*runnable_load(t). This means that we can compute all blocked entities at once by evaluating: blocked_load(cfs_rq)` = y * blocked_load(cfs_rq) Finally we maintain a decay counter so that when a sleeping entity re-awakens we can determine how much of its load should be removed from the blocked sum. Signed-off-by: Paul Turner Reviewed-by: Ben Segall Signed-off-by: Peter Zijlstra Link: http://lkml.kernel.org/r/20120823141506.585389902@google.com Signed-off-by: Ingo Molnar --- include/linux/sched.h | 1 + kernel/sched/core.c | 1 - kernel/sched/debug.c | 3 + kernel/sched/fair.c | 128 +++++++++++++++++++++++++++++++++++++----- kernel/sched/sched.h | 4 +- 5 files changed, 122 insertions(+), 15 deletions(-) diff --git a/include/linux/sched.h b/include/linux/sched.h index 81d8b1ba4100..b1831accfd89 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1103,6 +1103,7 @@ struct sched_avg { */ u32 runnable_avg_sum, runnable_avg_period; u64 last_runnable_update; + s64 decay_count; unsigned long load_avg_contrib; }; diff --git a/kernel/sched/core.c b/kernel/sched/core.c index fd9d0859350a..00898f1fb69e 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -1528,7 +1528,6 @@ static void __sched_fork(struct task_struct *p) p->se.avg.runnable_avg_period = 0; p->se.avg.runnable_avg_sum = 0; #endif - #ifdef CONFIG_SCHEDSTATS memset(&p->se.statistics, 0, sizeof(p->se.statistics)); #endif diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c index c953a89f94aa..2d2e2b3c1bef 100644 --- a/kernel/sched/debug.c +++ b/kernel/sched/debug.c @@ -95,6 +95,7 @@ static void print_cfs_group_stats(struct seq_file *m, int cpu, struct task_group P(se->avg.runnable_avg_sum); P(se->avg.runnable_avg_period); P(se->avg.load_avg_contrib); + P(se->avg.decay_count); #endif #undef PN #undef P @@ -227,6 +228,8 @@ void print_cfs_rq(struct seq_file *m, int cpu, struct cfs_rq *cfs_rq) atomic_read(&cfs_rq->tg->load_weight)); SEQ_printf(m, " .%-30s: %lld\n", "runnable_load_avg", cfs_rq->runnable_load_avg); + SEQ_printf(m, " .%-30s: %lld\n", "blocked_load_avg", + cfs_rq->blocked_load_avg); #endif print_cfs_group_stats(m, cpu, cfs_rq->tg); diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 77af759e5675..83194175e841 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -259,6 +259,8 @@ static inline struct cfs_rq *group_cfs_rq(struct sched_entity *grp) return grp->my_q; } +static void update_cfs_rq_blocked_load(struct cfs_rq *cfs_rq); + static inline void list_add_leaf_cfs_rq(struct cfs_rq *cfs_rq) { if (!cfs_rq->on_list) { @@ -278,6 +280,8 @@ static inline void list_add_leaf_cfs_rq(struct cfs_rq *cfs_rq) } cfs_rq->on_list = 1; + /* We should have no load, but we need to update last_decay. */ + update_cfs_rq_blocked_load(cfs_rq); } } @@ -1081,6 +1085,20 @@ static __always_inline int __update_entity_runnable_avg(u64 now, return decayed; } +/* Synchronize an entity's decay with its parenting cfs_rq.*/ +static inline void __synchronize_entity_decay(struct sched_entity *se) +{ + struct cfs_rq *cfs_rq = cfs_rq_of(se); + u64 decays = atomic64_read(&cfs_rq->decay_counter); + + decays -= se->avg.decay_count; + if (!decays) + return; + + se->avg.load_avg_contrib = decay_load(se->avg.load_avg_contrib, decays); + se->avg.decay_count = 0; +} + /* Compute the current contribution to load_avg by se, return any delta */ static long __update_entity_load_avg_contrib(struct sched_entity *se) { @@ -1096,8 +1114,18 @@ static long __update_entity_load_avg_contrib(struct sched_entity *se) return se->avg.load_avg_contrib - old_contrib; } +static inline void subtract_blocked_load_contrib(struct cfs_rq *cfs_rq, + long load_contrib) +{ + if (likely(load_contrib < cfs_rq->blocked_load_avg)) + cfs_rq->blocked_load_avg -= load_contrib; + else + cfs_rq->blocked_load_avg = 0; +} + /* Update a sched_entity's runnable average */ -static inline void update_entity_load_avg(struct sched_entity *se) +static inline void update_entity_load_avg(struct sched_entity *se, + int update_cfs_rq) { struct cfs_rq *cfs_rq = cfs_rq_of(se); long contrib_delta; @@ -1107,8 +1135,34 @@ static inline void update_entity_load_avg(struct sched_entity *se) return; contrib_delta = __update_entity_load_avg_contrib(se); + + if (!update_cfs_rq) + return; + if (se->on_rq) cfs_rq->runnable_load_avg += contrib_delta; + else + subtract_blocked_load_contrib(cfs_rq, -contrib_delta); +} + +/* + * Decay the load contributed by all blocked children and account this so that + * their contribution may appropriately discounted when they wake up. + */ +static void update_cfs_rq_blocked_load(struct cfs_rq *cfs_rq) +{ + u64 now = rq_of(cfs_rq)->clock_task >> 20; + u64 decays; + + decays = now - cfs_rq->last_decay; + if (!decays) + return; + + cfs_rq->blocked_load_avg = decay_load(cfs_rq->blocked_load_avg, + decays); + atomic64_add(decays, &cfs_rq->decay_counter); + + cfs_rq->last_decay = now; } static inline void update_rq_runnable_avg(struct rq *rq, int runnable) @@ -1118,26 +1172,53 @@ static inline void update_rq_runnable_avg(struct rq *rq, int runnable) /* Add the load generated by se into cfs_rq's child load-average */ static inline void enqueue_entity_load_avg(struct cfs_rq *cfs_rq, - struct sched_entity *se) + struct sched_entity *se, + int wakeup) { - update_entity_load_avg(se); + /* we track migrations using entity decay_count == 0 */ + if (unlikely(!se->avg.decay_count)) { + se->avg.last_runnable_update = rq_of(cfs_rq)->clock_task; + wakeup = 0; + } else { + __synchronize_entity_decay(se); + } + + if (wakeup) + subtract_blocked_load_contrib(cfs_rq, se->avg.load_avg_contrib); + + update_entity_load_avg(se, 0); cfs_rq->runnable_load_avg += se->avg.load_avg_contrib; + update_cfs_rq_blocked_load(cfs_rq); } -/* Remove se's load from this cfs_rq child load-average */ +/* + * Remove se's load from this cfs_rq child load-average, if the entity is + * transitioning to a blocked state we track its projected decay using + * blocked_load_avg. + */ static inline void dequeue_entity_load_avg(struct cfs_rq *cfs_rq, - struct sched_entity *se) + struct sched_entity *se, + int sleep) { - update_entity_load_avg(se); + update_entity_load_avg(se, 1); + cfs_rq->runnable_load_avg -= se->avg.load_avg_contrib; + if (sleep) { + cfs_rq->blocked_load_avg += se->avg.load_avg_contrib; + se->avg.decay_count = atomic64_read(&cfs_rq->decay_counter); + } /* migrations, e.g. sleep=0 leave decay_count == 0 */ } #else -static inline void update_entity_load_avg(struct sched_entity *se) {} +static inline void update_entity_load_avg(struct sched_entity *se, + int update_cfs_rq) {} static inline void update_rq_runnable_avg(struct rq *rq, int runnable) {} static inline void enqueue_entity_load_avg(struct cfs_rq *cfs_rq, - struct sched_entity *se) {} + struct sched_entity *se, + int wakeup) {} static inline void dequeue_entity_load_avg(struct cfs_rq *cfs_rq, - struct sched_entity *se) {} + struct sched_entity *se, + int sleep) {} +static inline void update_cfs_rq_blocked_load(struct cfs_rq *cfs_rq) {} #endif static void enqueue_sleeper(struct cfs_rq *cfs_rq, struct sched_entity *se) @@ -1266,7 +1347,7 @@ enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags) */ update_curr(cfs_rq); update_cfs_load(cfs_rq, 0); - enqueue_entity_load_avg(cfs_rq, se); + enqueue_entity_load_avg(cfs_rq, se, flags & ENQUEUE_WAKEUP); account_entity_enqueue(cfs_rq, se); update_cfs_shares(cfs_rq); @@ -1341,7 +1422,7 @@ dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags) * Update run-time statistics of the 'current'. */ update_curr(cfs_rq); - dequeue_entity_load_avg(cfs_rq, se); + dequeue_entity_load_avg(cfs_rq, se, flags & DEQUEUE_SLEEP); update_stats_dequeue(cfs_rq, se); if (flags & DEQUEUE_SLEEP) { @@ -1512,7 +1593,7 @@ static void put_prev_entity(struct cfs_rq *cfs_rq, struct sched_entity *prev) /* Put 'current' back into the tree. */ __enqueue_entity(cfs_rq, prev); /* in !on_rq case, update occurred at dequeue */ - update_entity_load_avg(prev); + update_entity_load_avg(prev, 1); } cfs_rq->curr = NULL; } @@ -1528,7 +1609,8 @@ entity_tick(struct cfs_rq *cfs_rq, struct sched_entity *curr, int queued) /* * Ensure that runnable average is periodically updated. */ - update_entity_load_avg(curr); + update_entity_load_avg(curr, 1); + update_cfs_rq_blocked_load(cfs_rq); /* * Update share accounting for long-running entities. @@ -2387,6 +2469,7 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags) update_cfs_load(cfs_rq, 0); update_cfs_shares(cfs_rq); + update_entity_load_avg(se, 1); } if (!se) { @@ -2448,6 +2531,7 @@ static void dequeue_task_fair(struct rq *rq, struct task_struct *p, int flags) update_cfs_load(cfs_rq, 0); update_cfs_shares(cfs_rq); + update_entity_load_avg(se, 1); } if (!se) { @@ -3498,6 +3582,7 @@ static int update_shares_cpu(struct task_group *tg, int cpu) update_rq_clock(rq); update_cfs_load(cfs_rq, 1); + update_cfs_rq_blocked_load(cfs_rq); /* * We need to update shares after updating tg->load_weight in @@ -5232,6 +5317,20 @@ static void switched_from_fair(struct rq *rq, struct task_struct *p) place_entity(cfs_rq, se, 0); se->vruntime -= cfs_rq->min_vruntime; } + +#if defined(CONFIG_FAIR_GROUP_SCHED) && defined(CONFIG_SMP) + /* + * Remove our load from contribution when we leave sched_fair + * and ensure we don't carry in an old decay_count if we + * switch back. + */ + if (p->se.avg.decay_count) { + struct cfs_rq *cfs_rq = cfs_rq_of(&p->se); + __synchronize_entity_decay(&p->se); + subtract_blocked_load_contrib(cfs_rq, + p->se.avg.load_avg_contrib); + } +#endif } /* @@ -5278,6 +5377,9 @@ void init_cfs_rq(struct cfs_rq *cfs_rq) #ifndef CONFIG_64BIT cfs_rq->min_vruntime_copy = cfs_rq->min_vruntime; #endif +#if defined(CONFIG_FAIR_GROUP_SCHED) && defined(CONFIG_SMP) + atomic64_set(&cfs_rq->decay_counter, 1); +#endif } #ifdef CONFIG_FAIR_GROUP_SCHED diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index e6539736af58..664ff39195f7 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -229,7 +229,9 @@ struct cfs_rq { * This allows for the description of both thread and group usage (in * the FAIR_GROUP_SCHED case). */ - u64 runnable_load_avg; + u64 runnable_load_avg, blocked_load_avg; + atomic64_t decay_counter; + u64 last_decay; #endif #ifdef CONFIG_FAIR_GROUP_SCHED struct rq *rq; /* cpu runqueue to which this cfs_rq is attached */