linux-kernel - Re: [PATCH v3 3/7] sched: throttle cfs_rq entities which exceed their local quota

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Date:	Thu, 14 Oct 2010 11:12:22 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	bharata@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org,
	Dhaval Giani <dhaval.giani@...il.com>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
	Srivatsa Vaddagiri <vatsa@...ibm.com>,
	Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	Pavel Emelyanov <xemul@...nvz.org>,
	Herbert Poetzl <herbert@...hfloor.at>,
	Avi Kivity <avi@...hat.com>,
	Chris Friesen <cfriesen@...tel.com>,
	Paul Menage <menage@...gle.com>,
	Mike Waychison <mikew@...gle.com>,
	Paul Turner <pjt@...gle.com>, Nikhil Rao <ncrao@...gle.com>
Subject: Re: [PATCH v3 3/7] sched: throttle cfs_rq entities which exceed
 their local quota

On Wed, 2010-10-13 at 15:34 +0900, KAMEZAWA Hiroyuki wrote:
> cpu.share and bandwidth control can't be used simultaneously or...
> is this fair ? I'm not familiar with scheduler but this allows boost this tg.
> Could you add a brief documentaion of a spec/feature. in the next post ?

Like explained, shares control the proportional distribution of time
between groups, bandwidth puts a limit on how much time a group can
take. It can cause a group to receive less than its fair share, but
never more.

There is, however, a problem with all this, and that is that all this
explicit idling of tasks can lead to a form of priority inversion.
Regular preemptive scheduling already suffers from this, but explicitly
idling tasks exacerbates the situation.

You basically get to add the longest induced idle time to all your lock
hold times.


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