Re: Stolen and degraded time and schedulers

From: Jeremy Fitzhardinge <jeremy@goop.org>
To: Lennart Sorensen <lsorense@csclub.uwaterloo.ca>
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>
Subject: Re: Stolen and degraded time and schedulers
Date: Wed, 14 Mar 2007 08:08:17 -0700	[thread overview]
Message-ID: <45F80FE1.3030603@goop.org> (raw)
In-Reply-To: <20070314135845.GG22466@csclub.uwaterloo.ca>

Lennart Sorensen wrote:
> How would you deal with something like a pentium 4 HT processor where
> you may run slower just because you got scheduled on the sibling of a
> cpu that happens to run something else needing the same execution units
> you do, causing you to get delayed more, even though the cpu is running
> full speed and nothing else is trying to use your "cpu"?  I don't think
> there is any way to know what the real impact of two processes on a HT
> cpu have on each other.
>
> Interesting goal.  Not sure it can be done.

You're right.  That's a very tough case.  I don't know if there's any
way to do a reasonable estimate of the slowdown.  You could handwave it
and say "if both threads are running a process, then apply an X scaling
factor to their rate of progress".  That might be enough.

    J