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

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Message-ID: <45F86C60.7060903@goop.org>
Date:	Wed, 14 Mar 2007 14:42:56 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Daniel Walker <dwalker@...sta.com>
CC:	john stultz <johnstul@...ibm.com>, Andi Kleen <ak@...e.de>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Con Kolivas <kernel@...ivas.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Zachary Amsden <zach@...are.com>,
	James Morris <jmorris@...ei.org>,
	Chris Wright <chrisw@...s-sol.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	cpufreq@...ts.linux.org.uk,
	Virtualization Mailing List <virtualization@...ts.osdl.org>,
	Peter Chubb <peterc@...ato.unsw.edu.au>
Subject: Re: Stolen and degraded time and schedulers

Daniel Walker wrote:
> It's used for measuring execution time, but timers are triggered based
> on that time, so it needs to be actual execution time. I don't know to
> what extent this is already inaccurate on some system tho.
>   

Well, "actual execution time" is a bit ambiguous: should that be "time
actually spent executing", or "time we should have spent executing"?

It looks like cpu_clock_sample() will only return accurate results on
yourself; if you get the sched_ns on a thread on another cpu, it won't
include the time accumulated since the start of its timeslice.

    J

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