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    SubjectRe: [patch 05/15] sched: add a timer to handle CFS bandwidth refresh
    On Mon, May 16, 2011 at 3:18 AM, Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:
    > On Tue, 2011-05-03 at 02:28 -0700, Paul Turner wrote:
    >> @@ -1003,6 +1003,8 @@ enqueue_entity(struct cfs_rq *cfs_rq, st
    >>
    >>         if (cfs_rq->nr_running == 1)
    >>                 list_add_leaf_cfs_rq(cfs_rq);
    >> +
    >> +       start_cfs_bandwidth(cfs_rq);
    >>  }
    >>
    >>  static void __clear_buddies_last(struct sched_entity *se)
    >> @@ -1220,6 +1222,8 @@ static void put_prev_entity(struct cfs_r
    >>                 update_stats_wait_start(cfs_rq, prev);
    >>                 /* Put 'current' back into the tree. */
    >>                 __enqueue_entity(cfs_rq, prev);
    >> +
    >> +               start_cfs_bandwidth(cfs_rq);
    >>         }
    >>         cfs_rq->curr = NULL;
    >>  }
    >
    > OK, so while the first made sense the second had me go wtf?!, now I
    > _think_ you do that because do_sched_cfs_period_timer() can return idle
    > and stop the timer when no bandwidth consumption is seen for a while,
    > and thus we need to re-start the timer when we put the entity to sleep,
    > since that could have been a throttle.
    >
    > If that's so then neither really do make sense and a big fat comment is
    > missing.
    >
    > So why not start on the same (but inverse) condition that makes it stop?
    >

    This was originally to guard the case that an entity was running on
    stale (from a previous period) quota resulting in cfs_bandwidth->idle
    and the timer not being re-instantiated.

    Now that expiration is properly integrated I think the two cases are
    analogous and that this can be dropped (and the start moved into the
    (nr_running == 1) entity case on enqueue).

    I think this is correct but my brain's a little fuzzy right now, will
    confirm in the morning.
    --
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