linux-kernel - Re: fair clock use in CFS

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Message-ID: <20070514103120.GA23766@elte.hu>
Date:	Mon, 14 May 2007 12:31:20 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	William Lee Irwin III <wli@...omorphy.com>
Cc:	Srivatsa Vaddagiri <vatsa@...ibm.com>, efault@....de,
	tingy@...umass.edu, linux-kernel@...r.kernel.org
Subject: Re: fair clock use in CFS


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

> On Mon, May 14, 2007 at 02:03:58PM +0530, Srivatsa Vaddagiri wrote:
> > 	I have been brooding over how fair clock is computed/used in
> > CFS and thought I would ask the experts to avoid wrong guesses!
> > As I understand, fair_clock is a monotonously increasing clock which
> > advances at a pace inversely proportional to the load on the runqueue.
> > If load = 1 (task), it will advance at same pace as wall clock, as 
> > load increases it advances slower than wall clock.
> > In addition, following calculations depend on fair clock: task's wait
> > time on runqueue and sleep time outside the runqueue (both reflected in
> > p->wait_run_time).
> 
> It's not hard to see that that's a mistake. [...]

please clarify - exactly what is a mistake? Thanks,

	Ingo
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