linux-kernel - Re: [patch] CFS scheduler, -v8

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Message-ID: <20070502181533.GA19479@elte.hu>
Date:	Wed, 2 May 2007 20:15:33 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	William Lee Irwin III <wli@...omorphy.com>
Cc:	Srivatsa Vaddagiri <vatsa@...ibm.com>,
	Ting Yang <tingy@...umass.edu>, linux-kernel@...r.kernel.org
Subject: Re: [patch] CFS scheduler, -v8


* William Lee Irwin III <wli@...omorphy.com> wrote:

> > There is also p->wait_runtime which is taken into account when 
> > calculating p->fair_key. So if p3 had waiting in runqueue for long 
> > before, it can get to run quicker than 10ms later.
> 
> Virtual time is time from the task's point of view, which it has spent 
> executing. ->wait_runtime is a device to subtract out time spent on 
> the runqueue but not running from what would otherwise be virtual time 
> to express lag, whether deliberately or coincidentally. [...]

CFS is in fact _built around_ the ->wait_runtime metric (which, as its 
name suggests already, expresses the precise lag a task observes 
relative to 'ideal' fair execution), so what exactly makes you suspect 
that this property of the ->wait_runtime metric might be 'coincidental'? 
;-)

	Ingo
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