linux-kernel - Re: [PATCH v8 1/4] sched: Remove rq's runnable avg

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Date:	Fri, 19 Jun 2015 19:27:24 +0100
From:	Dietmar Eggemann <dietmar.eggemann@....com>
To:	Yuyang Du <yuyang.du@...el.com>,
	"mingo@...nel.org" <mingo@...nel.org>,
	"peterz@...radead.org" <peterz@...radead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:	"pjt@...gle.com" <pjt@...gle.com>,
	"bsegall@...gle.com" <bsegall@...gle.com>,
	Morten Rasmussen <Morten.Rasmussen@....com>,
	"vincent.guittot@...aro.org" <vincent.guittot@...aro.org>,
	"arjan.van.de.ven@...el.com" <arjan.van.de.ven@...el.com>,
	"len.brown@...el.com" <len.brown@...el.com>,
	"rafael.j.wysocki@...el.com" <rafael.j.wysocki@...el.com>,
	"fengguang.wu@...el.com" <fengguang.wu@...el.com>,
	"boqun.feng@...il.com" <boqun.feng@...il.com>,
	"srikar@...ux.vnet.ibm.com" <srikar@...ux.vnet.ibm.com>
Subject: Re: [PATCH v8 1/4] sched: Remove rq's runnable avg

Hi Yuyang,

On 15/06/15 20:26, Yuyang Du wrote:
> The current rq->avg is not used at all since its merge into kernel,
> and the code is in the scheduler's hot path, so remove it.

are you sure that this is the case? I was always under the impression
that w/ CONFIG_FAIR_GROUP_SCHED=y rq->avg (runnable_avg_sum, avg_period)
is used to calculate contrib in __update_tg_runnable_avg() for the root
group (cfs_rq->tg->css.id = 1).

On tg's w/ cfs_rq->tg->css.id > 1, se->avg (runnable_avg_sum,
avg_period) is used instead but we simply don't have a tg related se for
the root group. IMHO, that's why we have this rq::avg.

I understand that w/ the second patch in your series you don't need
rq::avg any more.

[...]

-- Dietmar

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