linux-kernel - Re: [PATCH 7/7] sched: Track sched

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Date:	Mon, 22 Sep 2014 10:09:42 -0700
From:	bsegall@...gle.com
To:	Morten Rasmussen <morten.rasmussen@....com>
Cc:	peterz@...radead.org, mingo@...hat.com, dietmar.eggemann@....com,
	pjt@...gle.com, vincent.guittot@...aro.org,
	nicolas.pitre@...aro.org, mturquette@...aro.org, rjw@...ysocki.net,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 7/7] sched: Track sched_entity usage contributions

Morten Rasmussen <morten.rasmussen@....com> writes:

> Adds usage contribution tracking for both task and group entities.
> Maintains a non-priority scaled se->avg.usage_avg_contrib for each
> sched_entity and cfs_rq.usage_util_avg sum of all entity contributions.
> The latter provides a more accurate estimate of the true cpu utilization
> than the existing cfs_rq.runnable_load_avg (+blocked_load_avg).
>
> Unlike se->avg.load_avg_contrib, se->avg.usage_avg_contrib for group
> entities is the sum of se->avg.usage_avg_contrib for all entities on the
> group runqueue. It is _not_ influenced in any way by the task group
> h_load. Hence it is representing the actual cpu usage of the group, not
> its intended load contribution which may differ significantly from the
> usage on lightly utilized systems.
>
> The cpu usage tracking is available as cpu_rq(cpu)->cfs.usage_util_avg.
> No tracking of blocked usage has been implemented.

Isn't cfs_rq->usage_util_avg basically just
se->avg.usage_avg_sum * 1024 / se->avg.runnable_avg_period, where
se->group_cfs_rq == cfs_rq? (and for the rq as a whole, rq->avg)

The fact that usage_util_avg doesn't track blocked usage seems more
likely to be a problem than an advantage, but maybe not?
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