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Date: Thu, 14 Oct 2010 18:50:02 +0900
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: bharata@linux.vnet.ibm.com, linux-kernel@vger.kernel.org,
        Dhaval Giani <dhaval.giani@gmail.com>,
        Balbir Singh <balbir@linux.vnet.ibm.com>,
        Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>,
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        Mike Waychison <mikew@google.com>, Paul Turner <pjt@google.com>,
        Nikhil Rao <ncrao@google.com>
Subject: Re: [PATCH v3 3/7] sched: throttle cfs_rq entities which exceed
 their local quota
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On Thu, 14 Oct 2010 11:12:22 +0200
Peter Zijlstra <peterz@infradead.org> wrote:

> 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.
> 

What is the user-visible difference of the problem between
  1) limit share to be very small.
  2) use throttole.

If share is used, lock-hodler's priority is boosted ?

Thanks,
-Kame