Messages in this thread | | | Date | Fri, 19 Jun 2015 15:57:24 +0800 | From | Boqun Feng <> | Subject | Re: [PATCH v8 2/4] sched: Rewrite runnable load and utilization average tracking |
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Hi Yuyang,
On Fri, Jun 19, 2015 at 07:05:54AM +0800, Yuyang Du wrote: > 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.
Actually, I'm not sure whether we NEED to aggregate or NOT.
> > So simply updating the top cfs_rq is already equivalent to the stock. >
The stock does have a bottom up update, so simply updating the top cfs_rq is not equivalent to it. Simply updateing the top cfs_rq is equivalent to the rewrite patch, because the rewrite patch lacks of the aggregation.
> 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?
You get me right for most part ;-)
My points are:
1. We *may not* need to aggregate entity's load to cfs_rq in update_blocked_averages(), simply updating the top cfs_rq may be just fine, but I'm not sure, so scheduler experts' insights are needed here.
2. Whether we need to aggregate or not, the update_blocked_averages() in the rewrite patch could be improved. If we need to aggregate, we have to add something like update_cfs_shares(). If we don't need, we can just replace the loop with one update_cfs_rq_load_avg() on root cfs_rq.
I think we'd better to figure out the "may not" part in point 1 first to get a reasonable implemenation of update_blocked_averages().
Is that clear now?
Thanks and Best Regards, Boqun [unhandled content-type:application/pgp-signature] | |