linux-kernel - Re: [PATCH v9 1/4] sched: Remove rq's runnable avg

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Date:	Tue, 23 Jun 2015 17:49:44 +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>,
	"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 v9 1/4] sched: Remove rq's runnable avg

On 23/06/15 01:08, Yuyang Du wrote:
> The per-rq runnable averages (rq->avg) was introduced by Ben with this commit:
> 
> commit 18bf2805d9b30cb823d4919b42cd230f59c7ce1f
> Author: Ben Segall <bsegall@...gle.com>
> Date:   Thu Oct 4 12:51:20 2012 +0200
> 
>     sched: Maintain per-rq runnable averages
> 
>     Since runqueues do not have a corresponding sched_entity we instead embed a
>     sched_avg structure directly.
> 
>     Signed-off-by: Ben Segall <bsegall@...gle.com>
>     Reviewed-by: Paul Turner <pjt@...gle.com>
>     Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
>     Link: http://lkml.kernel.org/r/20120823141506.442637130@google.com
>     Signed-off-by: Ingo Molnar <mingo@...nel.org>
> 
> With CONFIG_FAIR_GROUP_SCHED=y, the rq->avg (runnable_avg_sum, avg_period) is
> used to calc the contrib in __update_tg_runnable_avg() for the root group.
> 
> But the root group's load data is never consumed since its merge into kernel
> in 2012. The basic reason is we have just one root group, and it is
> meaningless to give it weight. As the extra code is in the scheduler's
> hot path, so it is better to remove it.
> 
> Signed-off-by: Yuyang Du <yuyang.du@...el.com>

Reviewed-by: Dietmar Eggemann <dietmar.eggemann@....com>
Tested-by: Dietmar Eggemann <dietmar.eggemann@....com>

There is an additional clean-up possible since idle_[enter|exit]_fair()
are empty now.

[...]

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