On Fri, Jun 19, 2015 at 02:00:38PM +0800, Boqun Feng wrote:
> However, update_cfs_rq_load_avg() only updates cfs_rq->avg, the change
> won't be contributed or aggregated to cfs_rq's parent in the
> for_each_leaf_cfs_rq loop, therefore that's actually not a bottom-up
> update.
>
> To fix this, I think we can add a update_cfs_shares(cfs_rq) after
> update_cfs_rq_load_avg(). Like:
>
> for_each_leaf_cfs_rq(rq, cfs_rq) {
> - /*
> - * Note: We may want to consider periodically releasing
> - * rq->lock about these updates so that creating many task
> - * groups does not result in continually extending hold time.
> - */
> - __update_blocked_averages_cpu(cfs_rq->tg, rq->cpu);
> + /* throttled entities do not contribute to load */
> + if (throttled_hierarchy(cfs_rq))
> + continue;
> +
> + update_cfs_rq_load_avg(cfs_rq_clock_task(cfs_rq), cfs_rq);
> + update_cfs_share(cfs_rq);
> }
>
> However, I think update_cfs_share isn't cheap, because it may do a
> bottom-up update once called. So how about just update the root cfs_rq?
> Like:
>
> - /*
> - * Iterates the task_group tree in a bottom up fashion, see
> - * list_add_leaf_cfs_rq() for details.
> - */
> - for_each_leaf_cfs_rq(rq, cfs_rq) {
> - /*
> - * Note: We may want to consider periodically releasing
> - * rq->lock about these updates so that creating many task
> - * groups does not result in continually extending hold time.
> - */
> - __update_blocked_averages_cpu(cfs_rq->tg, rq->cpu);
> - }
> + update_cfs_rq_load_avg(rq_clock_task(rq), rq->cfs_rq);
Hi Boqun,
Did I get you right:
This rewrite patch does not NEED to aggregate entity's load to cfs_rq,
but rather directly update the cfs_rq's load (both runnable and blocked),
so there is NO NEED to iterate all of the cfs_rqs.
So simply updating the top cfs_rq is already equivalent to the stock.
It is better if we iterate the cfs_rq to update the actually weight
(update_cfs_share), because the weight may have already changed, which
would in turn change the load. But update_cfs_share is not cheap.
Right?
Thanks,
Yuyang
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
