linux-kernel - Re: [RFC PATCH 2/5] sched/events: Introduce cfs

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Message-ID: <cdf8bc6b-5ee8-0d15-1e50-a7cdbe9210a1@arm.com>
Date:   Tue, 28 Mar 2017 15:30:41 +0200
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Ingo Molnar <mingo@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Juri Lelli <juri.lelli@....com>,
        Patrick Bellasi <patrick.bellasi@....com>
Subject: Re: [RFC PATCH 2/5] sched/events: Introduce cfs_rq load tracking
 trace event

On 03/28/2017 09:56 AM, Peter Zijlstra wrote:
> On Tue, Mar 28, 2017 at 07:35:38AM +0100, Dietmar Eggemann wrote:

[...]

>>  (1) a root task_group:
>>
>>      cpu=4 path=/ id=1 load=6 util=331
>
> What's @id and why do we care?

It's a per cgroup/subsystem unique id for every task_group (cpu controller):

struct task_group {
	struct cgroup_subsys_state css {
		...
		int id;
                 ...
	}
	...
}

The root task group path=/ has id=1 and all autogroups have id=0.

I agree, this id is redundant in case we have the task_group path.