From 104cb16d9eb684f071d5bf3aa87c0d01af259b7c Mon Sep 17 00:00:00 2001 From: Morten Rasmussen Date: Fri, 14 Oct 2016 14:41:07 +0100 Subject: sched/fair: Compute task/cpu utilization at wake-up correctly At task wake-up load-tracking isn't updated until the task is enqueued. The task's own view of its utilization contribution may therefore not be aligned with its contribution to the cfs_rq load-tracking which may have been updated in the meantime. Basically, the task's own utilization hasn't yet accounted for the sleep decay, while the cfs_rq may have (partially). Estimating the cfs_rq utilization in case the task is migrated at wake-up as task_rq(p)->cfs.avg.util_avg - p->se.avg.util_avg is therefore incorrect as the two load-tracking signals aren't time synchronized (different last update). To solve this problem, this patch synchronizes the task utilization with its previous rq before the task utilization is used in the wake-up path. Currently the update/synchronization is done _after_ the task has been placed by select_task_rq_fair(). The synchronization is done without having to take the rq lock using the existing mechanism used in remove_entity_load_avg(). Signed-off-by: Morten Rasmussen Signed-off-by: Peter Zijlstra (Intel) Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: dietmar.eggemann@arm.com Cc: freedom.tan@mediatek.com Cc: keita.kobayashi.ym@renesas.com Cc: mgalbraith@suse.de Cc: sgurrappadi@nvidia.com Cc: vincent.guittot@linaro.org Cc: yuyang.du@intel.com Link: http://lkml.kernel.org/r/1476452472-24740-2-git-send-email-morten.rasmussen@arm.com Signed-off-by: Ingo Molnar --- kernel/sched/fair.c | 39 +++++++++++++++++++++++++++++++++++---- 1 file changed, 35 insertions(+), 4 deletions(-) (limited to 'kernel/sched/fair.c') diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 3cf446c53043..b05d691bbda8 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -3198,6 +3198,19 @@ static inline u64 cfs_rq_last_update_time(struct cfs_rq *cfs_rq) } #endif +/* + * Synchronize entity load avg of dequeued entity without locking + * the previous rq. + */ +void sync_entity_load_avg(struct sched_entity *se) +{ + struct cfs_rq *cfs_rq = cfs_rq_of(se); + u64 last_update_time; + + last_update_time = cfs_rq_last_update_time(cfs_rq); + __update_load_avg(last_update_time, cpu_of(rq_of(cfs_rq)), &se->avg, 0, 0, NULL); +} + /* * Task first catches up with cfs_rq, and then subtract * itself from the cfs_rq (task must be off the queue now). @@ -3205,7 +3218,6 @@ static inline u64 cfs_rq_last_update_time(struct cfs_rq *cfs_rq) void remove_entity_load_avg(struct sched_entity *se) { struct cfs_rq *cfs_rq = cfs_rq_of(se); - u64 last_update_time; /* * tasks cannot exit without having gone through wake_up_new_task() -> @@ -3217,9 +3229,7 @@ void remove_entity_load_avg(struct sched_entity *se) * calls this. */ - last_update_time = cfs_rq_last_update_time(cfs_rq); - - __update_load_avg(last_update_time, cpu_of(rq_of(cfs_rq)), &se->avg, 0, 0, NULL); + sync_entity_load_avg(se); atomic_long_add(se->avg.load_avg, &cfs_rq->removed_load_avg); atomic_long_add(se->avg.util_avg, &cfs_rq->removed_util_avg); } @@ -5582,6 +5592,24 @@ static inline int task_util(struct task_struct *p) return p->se.avg.util_avg; } +/* + * cpu_util_wake: Compute cpu utilization with any contributions from + * the waking task p removed. + */ +static int cpu_util_wake(int cpu, struct task_struct *p) +{ + unsigned long util, capacity; + + /* Task has no contribution or is new */ + if (cpu != task_cpu(p) || !p->se.avg.last_update_time) + return cpu_util(cpu); + + capacity = capacity_orig_of(cpu); + util = max_t(long, cpu_rq(cpu)->cfs.avg.util_avg - task_util(p), 0); + + return (util >= capacity) ? capacity : util; +} + /* * Disable WAKE_AFFINE in the case where task @p doesn't fit in the * capacity of either the waking CPU @cpu or the previous CPU @prev_cpu. @@ -5600,6 +5628,9 @@ static int wake_cap(struct task_struct *p, int cpu, int prev_cpu) if (max_cap - min_cap < max_cap >> 3) return 0; + /* Bring task utilization in sync with prev_cpu */ + sync_entity_load_avg(&p->se); + return min_cap * 1024 < task_util(p) * capacity_margin; } -- cgit v1.2.3