linux-kernel - Re: clocksource tsc unstable

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Message-ID: <Pine.LNX.4.64.0707101121110.11053@fbirervta.pbzchgretzou.qr>
Date:	Tue, 10 Jul 2007 11:22:21 +0200 (CEST)
From:	Jan Engelhardt <jengelh@...putergmbh.de>
To:	Pawel Dziepak <hryssta@...il.com>
cc:	"Renato S. Yamane" <renatoyamane@...dic.com.br>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: clocksource tsc unstable

On Jul 9 2007 22:54, Pawel Dziepak wrote:

> As far as i know Pentium M processors have dynamically changed clock
> speed (ofc to save power). That's why kernel notice that TSC is
> unstable (it is indeed). On my Athlon 64 I have similar situation,
> because CPU frequency is dynamically changed.
> I don't think that there is an easy way to fix it (it is not even a
> bug), time-stamp counter is not perfect...

Also see http://lkml.org/lkml/2007/5/6/29

The TSC is supposed to tick at the CPU rate (unless it's a constant_tsc, 
see /proc/cpuinfo flags:), so on frequency change, this ought to happen. 
The kernel will automatically switch to something else. There's acpi_pm 
and, IIRC, pit.


	Jan
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