linux-kernel - Re: fair clock use in CFS

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Message-ID: <20070514112016.GW19966@holomorphy.com>
Date:	Mon, 14 May 2007 04:20:16 -0700
From:	William Lee Irwin III <wli@...omorphy.com>
To:	Srivatsa Vaddagiri <vatsa@...ibm.com>
Cc:	Ingo Molnar <mingo@...e.hu>, efault@....de, tingy@...umass.edu,
	linux-kernel@...r.kernel.org
Subject: Re: fair clock use in CFS

On Mon, May 14, 2007 at 04:05:00AM -0700, William Lee Irwin III wrote:
>> The variability in ->fair_clock advancement rate was the mistake, at
>> least according to my way of thinking. The queue's virtual time clock
>> effectively stops under sufficiently high load, possibly literally in
>> the event of fixpoint underflow. 

On Mon, May 14, 2007 at 04:52:59PM +0530, Srivatsa Vaddagiri wrote:
> [snip]

On Mon, May 14, 2007 at 04:05:00AM -0700, William Lee Irwin III wrote:
>> Basically it needs to move closer to EEVDF in these respects.

On Mon, May 14, 2007 at 04:52:59PM +0530, Srivatsa Vaddagiri wrote:
> Doesn't EEVDF have the same issue? From the paper:
> 	V(t) = 1/(w1 + w2 + ...wn)

Who knows what I was smoking, then. I misremembered the scale factor
as being on the other side of comparisons with the queue's clock. I'm
suspicious of EEVDF's timekeeping now as well.


-- wli
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