linux-kernel - Re: RFC: cgroups aware proc

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Date:	Tue, 14 Jan 2014 11:05:41 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Marian Marinov <mm@...u.biz>
Cc:	lxc-devel@...ts.linuxcontainers.org, cgroups@...r.kernel.org,
	"Daniel P. Berrange" <berrange@...hat.com>,
	Serge Hallyn <serge.hallyn@...ntu.com>,
	Li Zefan <lizefan@...wei.com>, Ingo Molnar <mingo@...nel.org>,
	linux-kernel@...r.kernel.org
Subject: Re: RFC: cgroups aware proc

On Tue, Jan 14, 2014 at 02:58:14AM +0200, Marian Marinov wrote:
> On 01/13/2014 07:12 PM, Peter Zijlstra wrote:
> >On Mon, Jan 13, 2014 at 06:23:50PM +0200, Marian Marinov wrote:
> >>Hello Peter,
> >>
> >>I need help with the scheduler.
> >>
> >>I'm currently trying to patch the /proc/loadavg to show the load that is
> >>only related to the processes from the current cgroup.
> >>
> >>I looked trough the code and I was hoping that tsk->sched_task_group->cfs_rq
> >>struct will give me the needed information, but unfortunately for me, it did
> >>not.
> >>
> >>Can you advise me, how to approach this problem?
> >
> >Yeah, don't :-) Really, loadavg is a stupid metric.
> 
> Yes... stupid, but unfortunately everyone is looking at it :(
> 
> >
> >>I'm totally new to the scheduler code.
> >
> >Luckily you won't actually have to touch much of it. Most of the actual
> >loadavg code lives in the first ~400 lines of kernel/sched/proc.c, read
> >and weep. Its one of the best documented bits around.
> 
> I looked trough it but I don't understand how to introduce the per cgroup calculation.
> 
> I looked trough the headers and found the following, which is already implemented.
> 
>   task->sched_task_group->load_avg
>   task->sched_task_group->cfs_rq->load_avg
>   task->sched_task_group->cfs_rq->load.weight
>   task->sched_task_group->cfs_rq->runnable_load_avg
> 
> Unfortunately there is almost no documentation for these elements of the cfs_rq and task_group structs.
> 
> It seams to me that part of the per task group loadavg code is already present.

No, those are actual load metrics and completely unrelated to loadavg.

Loadavg requires per-cgroup-per-cpu variants of nr_running and
nr_uninterruptible.

Those are the only metrics used in kernel/sched/proc.c for loadavg.
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