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Subject: Re: [RFC PATCH 2/5] sched/events: Introduce cfs_rq load tracking
 trace event
To: Peter Zijlstra <peterz@infradead.org>
References: <20170328063541.12912-1-dietmar.eggemann@arm.com>
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Cc: Ingo Molnar <mingo@kernel.org>, LKML <linux-kernel@vger.kernel.org>,
        Matt Fleming <matt@codeblueprint.co.uk>,
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        Morten Rasmussen <morten.rasmussen@arm.com>,
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From: Dietmar Eggemann <dietmar.eggemann@arm.com>
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Date: Tue, 28 Mar 2017 15:30:41 +0200
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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.