Re: [RFC tg_shares_up improvements - v1 05/12] sched: fix update_cfs_load synchronization

Bharata B Rao
2010-10-21T09:52:41Z

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);
> }
>