linux-kernel - Re: [PATCH] raise tsc clocksource rating

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Message-ID: <47266DCE.1070309@goop.org>
Date:	Mon, 29 Oct 2007 16:33:34 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Zachary Amsden <zach@...are.com>,
	Glauber de Oliveira Costa <gcosta@...hat.com>,
	linux-kernel@...r.kernel.org, tglx@...utronix.de,
	rusty@...tcorp.com.au, Avi Kivity <avi@...ranet.com>,
	kvm-devel@...ts.sourceforge.net,
	Glauber de Oliveira Costa <glauber@....localdomain>,
	Dan Hecht <dhecht@...are.com>,
	Garrett Smith <garrett@...are.com>
Subject: Re: [PATCH] raise tsc clocksource rating

Ingo Molnar wrote:
> i dont remember us having discussed this before, ever. If there's any 
> "fight" about monotonicity and SMP then it would be a pretty onesided 
> affair, with you being beaten up seriously ;-)
>   

This is part of Xen's ABI, so it isn't easily changed.  You're right
that getting monotonicity is a pretty ugly affair of doing something
like "if (now < previous_return) return ++previous_return;", but its
better than using the tsc.

(Last time around, it was "Xen can't use the tsc because it can't ever
be used as a stable timebase" - though I don't think that was you
specifically.)

    J
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