From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ingo Molnar <mingo@elte.hu>
Subject: Re: [PATCH] raise tsc clocksource rating
Date: Mon, 29 Oct 2007 23:55:28 +0100
Message-ID: <20071029225528.GA31293@elte.hu>
References: <11936994092607-git-send-email-gcosta@redhat.com> <1193697734.9793.86.camel@bodhitayantram.eng.vmware.com> <20071029224852.GA27547@elte.hu> <47266431.1010500@goop.org>
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Cc: Zachary Amsden <zach@vmware.com>,
	Glauber de Oliveira Costa <gcosta@redhat.com>,
	linux-kernel@vger.kernel.org, tglx@linutronix.de,
	rusty@rustcorp.com.au, --cc@redhat.com, avi@quramnet.com,
	kvm-devel@lists.sourceforge.net,
	Glauber de Oliveira Costa <glauber@t60.localdomain>,
	Dan Hecht <dhecht@vmware.com>,
	Garrett Smith <garrett@vmware.com>
To: Jeremy Fitzhardinge <jeremy@goop.org>
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* Jeremy Fitzhardinge <jeremy@goop.org> wrote:

> > if it's inaccurate why are you exposing it to the guest then? Native 
> > only uses the TSC if it's safe and accurate to do so.
> 
> It is used as part of the Xen clocksource as a short term 
> extrapolator, with correction parameters supplied by the hypervisor.  
> It should never be used directly.

that's totally broken then. You cannot create an SMP-safe monotonic 
clocksource via interpolation - native does not do it either. Good thing 
this problem got exposed, it needs to be fixed.

	Ingo