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    SubjectRe: [patch v8 4/9] sched: fix slept time double counting in enqueue entity
    On Fri, Jun 7, 2013 at 12:20 AM, Alex Shi <alex.shi@intel.com> wrote:
    > The wakeuped migrated task will __synchronize_entity_decay(se); in
    > migrate_task_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 slept time is updated
    > twice for se.avg.load_avg_contrib in both __syncchronize and
    > update_entity_load_avg.
    >
    > but if the slept task is waked up from self cpu, it miss the
    > last_runnable_update before update_entity_load_avg(se, 0, 1), then the
    > slept time was used twice in both functions.
    > So we need to remove the double slept time counting.

    Good catch.

    >
    > Signed-off-by: Alex Shi <alex.shi@intel.com>
    > ---
    > kernel/sched/fair.c | 3 ++-
    > 1 file changed, 2 insertions(+), 1 deletion(-)
    >
    > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
    > index 1fc30b9..42c7be0 100644
    > --- a/kernel/sched/fair.c
    > +++ b/kernel/sched/fair.c
    > @@ -1570,7 +1570,8 @@ static inline void enqueue_entity_load_avg(struct cfs_rq *cfs_rq,
    > }
    > wakeup = 0;
    > } else {
    > - __synchronize_entity_decay(se);
    > + se->avg.last_runnable_update += __synchronize_entity_decay(se)
    > + << 20;

    Can you add something like:

    + /*
    + * 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.
    + */


    Reviewed-by: Paul Turner <pjt@google.com>


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