Re: Stolen and degraded time and schedulers

From: Daniel Walker <dwalker@mvista.com>
To: Jeremy Fitzhardinge <jeremy@goop.org>
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>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	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
Date: Wed, 14 Mar 2007 13:33:58 -0700	[thread overview]
Message-ID: <1173904438.3101.92.camel@imap.mvista.com> (raw)
In-Reply-To: <45F8508F.3070109@goop.org>

On Wed, 2007-03-14 at 12:44 -0700, Jeremy Fitzhardinge wrote:
> Daniel Walker wrote:
> > sched_clock is used to bank real time against some specific states
> > inside the scheduler, and no it doesn't _just_ measure a processes
> > executing time.
> >   
> 
> Could you point these places out?  All uses of sched_clock() that I
> could see in kernel/sched.c seemed to be related to working out how
> long
> something spent executing, either in the scheduler proper, or
> benchmarking cache characteristics. 

For interactive tasks (basic scheduling) the execution time, and sleep
time need to be measured. It's also used for some posix cpu timers
(sched_ns) , and it used for migration thread initialization. I'm sure
it's used for a variety of out-of-tree random timing as well..

Daniel