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sched/fair: Fix the dealing with decay_count in __synchronize_entity_decay()

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In __synchronize_entity_decay(), if "decays" happens to be zero,
se->avg.decay_count will not be zeroed, holding the positive value
assigned when dequeued last time.

This is problematic in the following case:
If this runnable task is CFS-balanced to other CPUs soon afterwards,
migrate_task_rq_fair() will treat it as a blocked task due to its
non-zero decay_count, thereby adding its load to cfs_rq->removed_load
wrongly.

Thus, we must zero se->avg.decay_count in this case as well.

Signed-off-by: Xunlei Pang <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Reviewed-by: Ben Segall <[email protected]>
Cc: Linus Torvalds <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>
This commit is contained in:
Xunlei Pang 2014-12-16 23:58:29 +08:00 • committed by Ingo Molnar
commit 638476007d
1 changed files with 1 additions and 1 deletions
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2
kernel/sched/fair.c
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@ -2574,11 +2574,11 @@ static inline u64 __synchronize_entity_decay(struct sched_entity *se)
u64 decays = atomic64_read(&cfs_rq->decay_counter);
decays -= se->avg.decay_count;
se->avg.decay_count = 0;
if (!decays)
return 0;
se->avg.load_avg_contrib = decay_load(se->avg.load_avg_contrib, decays);
se->avg.decay_count = 0;
return decays;
}