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sched: Fix sleep time double accounting in enqueue entity

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The woken migrated task will __synchronize_entity_decay(se); in
migrate_task_rq_fair, then it needs to set
`se->avg.last_runnable_update -= (-se->avg.decay_count) << 20' before
update_entity_load_avg, in order to avoid sleep time is updated twice
for se.avg.load_avg_contrib in both __syncchronize and
update_entity_load_avg.

However if the sleeping task is woken up from the same cpu, it miss
the last_runnable_update before update_entity_load_avg(se, 0, 1), then
the sleep time was used twice in both functions.  So we need to remove
the double sleep time accounting.

Paul also contributed some code comments in this commit.

Signed-off-by: Alex Shi <[email protected]>
Reviewed-by: Paul Turner <[email protected]>
Signed-off-by: Peter Zijlstra <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>
This commit is contained in:
Alex Shi 2013-06-20 10:18:48 +08:00 • committed by Ingo Molnar
commit 282cf499f0
1 changed files with 7 additions and 1 deletions
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8
kernel/sched/fair.c
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@ -1571,7 +1571,13 @@ static inline void enqueue_entity_load_avg(struct cfs_rq *cfs_rq,
}
wakeup = 0;
} else {
__synchronize_entity_decay(se);
/*
* Task re-woke on same cpu (or else migrate_task_rq_fair()
* would have made count negative); we must be careful to avoid
* double-accounting blocked time after synchronizing decays.
*/
se->avg.last_runnable_update += __synchronize_entity_decay(se)
<< 20;
}
/* migrated tasks did not contribute to our blocked load */