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

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Message-ID: <45F8663D.5050102@goop.org>
Date:	Wed, 14 Mar 2007 14:16:45 -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>,
	Peter Chubb <peterc@...ato.unsw.edu.au>
Subject: Re: Stolen and degraded time and schedulers

Daniel Walker wrote:
> For interactive tasks (basic scheduling) the execution time, and sleep
> time need to be measured.

Sleep time is interesting.  It doesn't make much sense to talk about
time that was stolen while a process was sleeping (it was either stolen
from another running process, or the VCPU was just plain idle).  Also,
the definition of sched_clock I'm talking about is inherently per-cpu,
and sleeping has nothing to do with any cpu by definition.

So something other than sched_clock should be used to measure sleep
time, but it needs to produce interval measurements which are in the
same units as sched_clock.

>  It's also used for some posix cpu timers
> (sched_ns) , and it used for migration thread initialization.

sched_ns doesn't use it directly except for the case where the process
is currently running.  Anyway, it's compatible with what I'm talking about.

>  I'm sure
> it's used for a variety of out-of-tree random timing as well..
>   

Yeah, well...

    J
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