Re: Stolen and degraded time and schedulers

From: Rik van Riel <riel@redhat.com>
To: Jeremy Fitzhardinge <jeremy@goop.org>
Cc: Dan Hecht <dhecht@vmware.com>,
	dwalker@mvista.com, cpufreq@lists.linux.org.uk,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Con Kolivas <kernel@kolivas.org>,
	Chris Wright <chrisw@sous-sol.org>,
	Virtualization Mailing List <virtualization@lists.osdl.org>,
	john stultz <johnstul@us.ibm.com>, Ingo Molnar <mingo@elte.hu>,
	Thomas Gleixner <tglx@linutronix.de>,
	paulus@au.ibm.com, schwidefsky@de.ibm.com
Subject: Re: Stolen and degraded time and schedulers
Date: Wed, 14 Mar 2007 15:45:03 -0400	[thread overview]
Message-ID: <45F850BF.5030702@redhat.com> (raw)
In-Reply-To: <45F84E39.7030507@goop.org>

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.

-- 
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