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Date: Wed, 14 Mar 2007 14:16:45 -0700
From: Jeremy Fitzhardinge <jeremy@goop.org>
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To: Daniel Walker <dwalker@mvista.com>
CC: john stultz <johnstul@us.ibm.com>, Andi Kleen <ak@suse.de>,
       Ingo Molnar <mingo@elte.hu>, Thomas Gleixner <tglx@linutronix.de>,
       Con Kolivas <kernel@kolivas.org>, Rusty Russell <rusty@rustcorp.com.au>,
       Zachary Amsden <zach@vmware.com>, James Morris <jmorris@namei.org>,
       Chris Wright <chrisw@sous-sol.org>,
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       cpufreq@lists.linux.org.uk,
       Virtualization Mailing List <virtualization@lists.osdl.org>,
       Peter Chubb <peterc@gelato.unsw.edu.au>
Subject: Re: Stolen and degraded time and schedulers
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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