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    SubjectRe: [RFC tg_shares_up improvements - v1 05/12] sched: fix update_cfs_load synchronization
    On Fri, Oct 15, 2010 at 09:43:54PM -0700, pjt@google.com wrote:
    > Using cfs_rq->nr_running is not sufficient to synchronize update_cfs_load with
    > the put path since nr_running accounting occurs at deactivation.
    >
    > It's also not safe to make the removal decision based on load_avg as this fails
    > with both high periods and low shares. Resolve this by clipping history at 8
    > foldings.
    >

    Did you mean 4 foldings (and not 8) above since I see you are truncating
    the load history at 4 idle periods ?


    > @@ -685,9 +686,19 @@ static void update_cfs_load(struct cfs_r
    > now = rq_of(cfs_rq)->clock;
    > delta = now - cfs_rq->load_stamp;
    >
    > + /* truncate load history at 4 idle periods */
    > + if (cfs_rq->load_stamp > cfs_rq->load_last &&
    > + now - cfs_rq->load_last > 4 * period) {
    > + cfs_rq->load_period = 0;
    > + cfs_rq->load_avg = 0;
    > + }
    > +
    > cfs_rq->load_stamp = now;
    > cfs_rq->load_period += delta;
    > - cfs_rq->load_avg += delta * cfs_rq->load.weight;
    > + if (load) {
    > + cfs_rq->load_last = now;
    > + cfs_rq->load_avg += delta * load;
    > + }
    >
    > while (cfs_rq->load_period > period) {
    > /*
    > @@ -700,10 +711,8 @@ static void update_cfs_load(struct cfs_r
    > cfs_rq->load_avg /= 2;
    > }
    >
    > - if (lb && !cfs_rq->nr_running) {
    > - if (cfs_rq->load_avg < (period / 8))
    > - list_del_leaf_cfs_rq(cfs_rq);
    > - }
    > + if (!cfs_rq->curr && !cfs_rq->nr_running && !cfs_rq->load_avg)
    > + list_del_leaf_cfs_rq(cfs_rq);
    > }
    >


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