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

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Message-ID: <45F850BF.5030702@redhat.com>
Date:	Wed, 14 Mar 2007 15:45:03 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
CC:	Dan Hecht <dhecht@...are.com>, dwalker@...sta.com,
	cpufreq@...ts.linux.org.uk,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Con Kolivas <kernel@...ivas.org>,
	Chris Wright <chrisw@...s-sol.org>,
	Virtualization Mailing List <virtualization@...ts.osdl.org>,
	john stultz <johnstul@...ibm.com>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>, paulus@...ibm.com,
	schwidefsky@...ibm.com
Subject: Re: Stolen and degraded time and schedulers

Jeremy Fitzhardinge wrote:

>> How is time quantum getting stolen less important?  Time quantum
>> getting stolen results directly in more unnecessary context switches
>> since we might steal the entire timeslice before the process even ran.
> 
> It doesn't matter why you didn't get the time; 

Oh, but it does.

System administrators can use steal time the same way they
use iowait time: to spot bottlenecks on their systems.

If you have a lot of iowait time, you know you want either
faster IO or more memory.

If you have a lot of steal time, you know you need to spread
your virtual machines over more CPUs.

Steal time allows you to see the difference between a busy
system and an overloaded system.

-- 
Politics is the struggle between those who want to make their country
the best in the world, and those who believe it already is.  Each group
calls the other unpatriotic.
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