@@ -2689,15 +2689,18 @@ static void reweight_entity(struct cfs_rq *cfs_rq, struct sched_entity *se,
static inline int throttled_hierarchy(struct cfs_rq *cfs_rq);
-static void update_cfs_shares(struct cfs_rq *cfs_rq)
+static void update_cfs_shares(struct sched_entity *se)
{
struct task_group *tg;
- struct sched_entity *se;
+ struct cfs_rq *cfs_rq = group_cfs_rq(se);
long shares;
+ if (entity_is_task(se))
+ return;
+
tg = cfs_rq->tg;
- se = tg->se[cpu_of(rq_of(cfs_rq))];
- if (!se || throttled_hierarchy(cfs_rq))
+
+ if (throttled_hierarchy(cfs_rq))
return;
#ifndef CONFIG_SMP
if (likely(se->load.weight == tg->shares))
@@ -2707,8 +2710,10 @@ static void update_cfs_shares(struct cfs_rq *cfs_rq)
reweight_entity(cfs_rq_of(se), se, shares);
}
+
+
#else /* CONFIG_FAIR_GROUP_SCHED */
-static inline void update_cfs_shares(struct cfs_rq *cfs_rq)
+static inline void update_cfs_shares(struct sched_entity *se)
{
}
#endif /* CONFIG_FAIR_GROUP_SCHED */
@@ -3583,9 +3588,9 @@ enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
se->vruntime += cfs_rq->min_vruntime;
update_load_avg(se, UPDATE_TG);
+ update_cfs_shares(se);
enqueue_entity_load_avg(cfs_rq, se);
account_entity_enqueue(cfs_rq, se);
- update_cfs_shares(cfs_rq);
if (flags & ENQUEUE_WAKEUP)
place_entity(cfs_rq, se, 0);
@@ -3681,7 +3686,7 @@ dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
/* return excess runtime on last dequeue */
return_cfs_rq_runtime(cfs_rq);
- update_cfs_shares(cfs_rq);
+ update_cfs_shares(se);
/*
* Now advance min_vruntime if @se was the entity holding it back,
@@ -3864,7 +3869,7 @@ entity_tick(struct cfs_rq *cfs_rq, struct sched_entity *curr, int queued)
* Ensure that runnable average is periodically updated.
*/
update_load_avg(curr, UPDATE_TG);
- update_cfs_shares(cfs_rq);
+ update_cfs_shares(curr);
#ifdef CONFIG_SCHED_HRTICK
/*
@@ -4761,7 +4766,7 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
break;
update_load_avg(se, UPDATE_TG);
- update_cfs_shares(cfs_rq);
+ update_cfs_shares(se);
}
if (!se)
@@ -4820,7 +4825,7 @@ static void dequeue_task_fair(struct rq *rq, struct task_struct *p, int flags)
break;
update_load_avg(se, UPDATE_TG);
- update_cfs_shares(cfs_rq);
+ update_cfs_shares(se);
}
if (!se)
@@ -9316,7 +9321,7 @@ int sched_group_set_shares(struct task_group *tg, unsigned long shares)
/* Possible calls to update_curr() need rq clock */
update_rq_clock(rq);
for_each_sched_entity(se)
- update_cfs_shares(group_cfs_rq(se));
+ update_cfs_shares(se);
raw_spin_unlock_irqrestore(&rq->lock, flags);
}
The update of the share of a cfs_rq is done when its load_avg is updated but before the group_entity's load_avg has been updated for the past time slot. This generates wrong load_avg accounting which can be significant when small tasks are involved in the scheduling. Let take the example of a task TA that is dequeued of its task group TG1. TA was the only task in TG1 which becomes idle. We have the sequence: - dequeue_entity TA->se - update_load_avg(TA->se) - dequeue_entity_load_avg(TG1->cfs_rq, TA->se) - account_entity_dequeue(TG1->cfs_rq, TA->se) TG1->cfs_rq->load.weight = 0 - update_cfs_shares(TG1->cfs_rq) TG1->se->load.weight is updated with the new share of cfs_rq. TG1->se->load.weight = 0. - dequeue_entity TG1->se - update_load_avg(TG1->se) but its weight is now null so the last time slot (up to a tick) will be accounted with its new weight (0 in our case) instead of its real weight. The last time slot is accounted as an idle one whereas it was a running one. If the running time of TA is short enough that no tick happens when it runs, all running time of TG1->se will be accounted as idle time. Instead, we should update the share of a cfs_rq (in fact the weight of its group entity) only after having updated the load_avg of the group_entity. update_cfs_shares() now takes the sched_entity as parameter instead of the cfs_rq and the weight of the group_entity is updated only once its load_avg has been synced with current time. Cc: <stable@vger.kernel.org> Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org> --- I have seen the problem on tip/sched/core, v4.8 and v4.7. Previous versions might also have the problem but I haven't not been able to test them yet. kernel/sched/fair.c | 27 ++++++++++++++++----------- 1 file changed, 16 insertions(+), 11 deletions(-) -- 2.7.4