linux-kernel - RE: [PATCH] Option to synchronize P-states for AMD family 0xf

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Message-ID: <DDE95BDD51FB774B804A9C029E735EE10379BEDA68@sausexmbp02.amd.com>
Date:	Wed, 30 Sep 2009 09:30:57 -0500
From:	"Langsdorf, Mark" <mark.langsdorf@....com>
To:	"'Joerg Roedel'" <joro@...tes.org>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Sarathy, Bhavna" <Bhavna.Sarathy@....com>,
	"davej@...hat.com" <davej@...hat.com>
Subject: RE: [PATCH] Option to synchronize P-states for  AMD family 0xf

> > AMD Family 0xf processors (Athlon 64s and Opterons) do not
> > have P-State or C-State invariant TSCs.  Instead, the TSC
> > increments at the current processor frequency, which makes
> > it unstable and unreliable if cpufreq is enabled.
> > 
> > This patch introduces a new command parameter for the
> > PowerNow! driver called "tscsync".  When tscsync is
> > set to 1, the driver forces all processors in the system
> > to change frequency as the same time to the same frequency.
> > This unified change means that all the TSCs in the system
> > increment at the same rate.
> 
> Cool feature. Does Linux consider the TSC as stable on these machines
> even after a longer uptime (say after a week)?

Ask me in a week.  Linux time-keeping code has evolved
quite a bit since I last looked at this code.

-Mark Langsdorf
Operating System Research Center
AMD
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