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

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Message-ID: <20090930100059.GG29634@8bytes.org>
Date:	Wed, 30 Sep 2009 12:00:59 +0200
From:	Joerg Roedel <joro@...tes.org>
To:	Mark Langsdorf <mark.langsdorf@....com>
Cc:	linux-kernel@...r.kernel.org, bhavna.sarathy@....com,
	davej@...hat.com
Subject: Re: [PATCH] Option to synchronize P-states for  AMD family 0xf

On Tue, Sep 29, 2009 at 04:23:55PM -0500, Mark Langsdorf wrote:

> 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)?

	Joerg

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