sched: Prevent buddy interactions with throttled entities
Buddies allow us to select "on-rq" entities without actually selecting them from a cfs_rq's rb_tree. As a result we must ensure that throttled entities are not falsely nominated as buddies. The fact that entities are dequeued within throttle_entity is not sufficient for clearing buddy status as the nomination may occur after throttling. Signed-off-by: Paul Turner <pjt@google.com> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Link: http://lkml.kernel.org/r/20110721184757.886850167@google.com Signed-off-by: Ingo Molnar <mingo@elte.hu>
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@ -2348,6 +2348,15 @@ static void check_preempt_wakeup(struct rq *rq, struct task_struct *p, int wake_
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if (unlikely(se == pse))
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if (unlikely(se == pse))
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return;
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return;
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/*
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* This is possible from callers such as pull_task(), in which we
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* unconditionally check_prempt_curr() after an enqueue (which may have
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* lead to a throttle). This both saves work and prevents false
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* next-buddy nomination below.
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*/
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if (unlikely(throttled_hierarchy(cfs_rq_of(pse))))
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return;
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if (sched_feat(NEXT_BUDDY) && scale && !(wake_flags & WF_FORK)) {
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if (sched_feat(NEXT_BUDDY) && scale && !(wake_flags & WF_FORK)) {
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set_next_buddy(pse);
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set_next_buddy(pse);
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next_buddy_marked = 1;
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next_buddy_marked = 1;
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@ -2356,6 +2365,12 @@ static void check_preempt_wakeup(struct rq *rq, struct task_struct *p, int wake_
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/*
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/*
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* We can come here with TIF_NEED_RESCHED already set from new task
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* We can come here with TIF_NEED_RESCHED already set from new task
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* wake up path.
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* wake up path.
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*
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* Note: this also catches the edge-case of curr being in a throttled
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* group (e.g. via set_curr_task), since update_curr() (in the
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* enqueue of curr) will have resulted in resched being set. This
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* prevents us from potentially nominating it as a false LAST_BUDDY
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* below.
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*/
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*/
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if (test_tsk_need_resched(curr))
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if (test_tsk_need_resched(curr))
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return;
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return;
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@ -2474,7 +2489,8 @@ static bool yield_to_task_fair(struct rq *rq, struct task_struct *p, bool preemp
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{
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{
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struct sched_entity *se = &p->se;
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struct sched_entity *se = &p->se;
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if (!se->on_rq)
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/* throttled hierarchies are not runnable */
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if (!se->on_rq || throttled_hierarchy(cfs_rq_of(se)))
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return false;
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return false;
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/* Tell the scheduler that we'd really like pse to run next. */
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/* Tell the scheduler that we'd really like pse to run next. */
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