linux-kernel - Re: Stolen and degraded time and schedulers

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Date:	Wed, 14 Mar 2007 09:37:18 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Daniel Walker <dwalker@...sta.com>
CC:	john stultz <johnstul@...ibm.com>, Andi Kleen <ak@...e.de>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Con Kolivas <kernel@...ivas.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Zachary Amsden <zach@...are.com>,
	James Morris <jmorris@...ei.org>,
	Chris Wright <chrisw@...s-sol.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	cpufreq@...ts.linux.org.uk,
	Virtualization Mailing List <virtualization@...ts.osdl.org>
Subject: Re: Stolen and degraded time and schedulers

Daniel Walker wrote:
> Then your direction is wrong, sched_clock() should be constant ideally
> (1millisecond should really be 1millisecond). 

Rather than repeating myself, I suggest you read my original post
again.  But my point is that "I was runnable on a cpu for 1ms of real
time" is a meaningless measurement: you want to measure "I ran for 1
cpu-ms", which is a unit which depends on how work a particular CPU does
in relationship to other CPUs on the system, or even itself at some
previous time.

> Like I said in the last
> email, change the scheduler to make it aware of the variable quantum
> values.

I suppose you could, but that seems more complex.  I think you could
encode the same information in the measurement of how much work a cpu
actually got done while a process was scheduled on it.

    J
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