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Date: Fri, 19 Jun 2015 07:05:54 +0800 From: Yuyang Du <yuyang.du@...el.com> To: Boqun Feng <boqun.feng@...il.com> Cc: mingo@...nel.org, peterz@...radead.org, linux-kernel@...r.kernel.org, pjt@...gle.com, bsegall@...gle.com, morten.rasmussen@....com, vincent.guittot@...aro.org, dietmar.eggemann@....com, len.brown@...el.com, rafael.j.wysocki@...el.com, fengguang.wu@...el.com, srikar@...ux.vnet.ibm.com Subject: Re: [PATCH v8 2/4] sched: Rewrite runnable load and utilization average tracking 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 majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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