linux-kernel - Re: [PATCH] sched: select 'idle' cfs_rq per task-group to prevent tg-internal imbalance

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Message-ID: <20140701085658.GM6758@twins.programming.kicks-ass.net>
Date:	Tue, 1 Jul 2014 10:56:58 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Michael wang <wangyun@...ux.vnet.ibm.com>
Cc:	Mike Galbraith <umgwanakikbuti@...il.com>,
	Rik van Riel <riel@...hat.com>,
	Ingo Molnar <mingo@...nel.org>, Alex Shi <alex.shi@...aro.org>,
	Paul Turner <pjt@...gle.com>, Mel Gorman <mgorman@...e.de>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] sched: select 'idle' cfs_rq per task-group to prevent
 tg-internal imbalance

On Tue, Jul 01, 2014 at 04:38:58PM +0800, Michael wang wrote:
> On 07/01/2014 04:20 PM, Peter Zijlstra wrote:
> [snip]
> >>
> >> Just wondering could we make this another scheduler feature?
> > 
> > No; sched_feat() is for debugging, BIG CLUE: its guarded by
> > CONFIG_SCHED_DEBUG, anybody using it in production or anywhere else is
> > broken.
> > 
> > If people are using it, I should remove or at least randomize the
> > interface.
> 
> Fair enough... but is there any suggestions on how to handle this issue?
> 
> Currently when dbench running with stress, it could only gain one CPU,
> and cpu-cgroup cpu.shares is meaningless, is there any good methods to
> address that?

So as far as I understood this is because of 'other' tasks; these other
tasks have never been fully qualified, but I suspect they're workqueue
thingies. One solution would be to have work run in the same cgroup as
the task creating it.

The thing is, this is not a scheduler problem, so we should not fix it
in the scheduler.

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