linux-kernel - Re: TSC as clocksource

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Message-ID: <alpine.LFD.2.00.1101101452290.12146@localhost6.localdomain6>
Date:	Mon, 10 Jan 2011 14:54:45 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Peter Zijlstra <peterz@...radead.org>
cc:	Rob <roblinux@...il.com>, linux-kernel@...r.kernel.org,
	"Brown, Len" <lenb@...nel.org>
Subject: Re: TSC as clocksource

On Mon, 10 Jan 2011, Peter Zijlstra wrote:

> On Mon, 2011-01-10 at 09:54 +1100, Rob wrote:
> > Want to use TSC as clocksource
> > have a Intel Core2 Duo with constant_tsc flag
> > TSC should be stable at C1 + C2, it is debatable whether C3 is stable
> > 
> > Using processor.max_cstate=2 to use only C1 + C2 changes nothing, still get
> > Monitor-Mwait will be used to enter C-3 state
> > there should be checks before this is forced

We unconditinally set TSC unstable for anything > C1. The reason is
that we had a lot of troubles with BIOSes which advertise C2, but in
fact implement C3. Unfortunately we can't verify that.

Thanks,

	tglx
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