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

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Message-ID: <45F9A788.1010008@vmware.com>
Date:	Thu, 15 Mar 2007 13:07:36 -0700
From:	Dan Hecht <dhecht@...are.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	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, Rik van Riel <riel@...hat.com>,
	Zachary Amsden <zach@...are.com>
Subject: Re: Stolen and degraded time and schedulers

On 03/15/2007 12:53 PM, Jeremy Fitzhardinge wrote:
> Dan Hecht wrote:
>> Available time is defined to be (real_time - stolen_time).  i.e. time
>> in which the vcpu is either running or not ready to run [because it is
>> halted, and nothing is pending]).
> 
> Hm, the Xen definition of stolen time is "time VCPU spent in runnable
> (vs running) or offline state".  If the VCPU was blocked anyway, then
> its never considered to be stolen.  Offline means the VCPU was paused by
> the administrator, or during suspend/resume.
> 
>

Yes, the part in the "i.e." above is describing available time.  So, it 
is essentially is the same definition of stolen time VMI uses:

stolen time     == ready to run but not running
available time  == running or not ready to run

Basically, a vcpu starts off running (and this time is counted as 
available time).  Eventually, it will either be preempted by the 
hypervisor and descheduled (then this time becomes stolen since the vcpu 
is still ready), or it will decide to halt (then the time remains 
accounted towards available time).  Once the vcpu is halted, then 
eventually something happens and we should deliver a virtual interrupt 
to the vcpu.  The time between that something happening (e.g. host I/O 
completing, an alarm expiring) and the vcpu actually starting to run 
again is accounted as stolen.

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