linux-kernel - Re: exposing FSB clock speed in /sys

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Message-ID: <20070331100209.GA17761@one.firstfloor.org>
Date:	Sat, 31 Mar 2007 12:02:09 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Stephane Eranian <eranian@....hp.com>
Cc:	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org,
	perfmon@...ali.hpl.hp.com
Subject: Re: exposing FSB clock speed in /sys


> I am not interested in older processors, but I think for all recent Intel
> processors, there is a fairly simple algorithm to get the frequency using
> a couple of MSRs (including MSR_IA32_EBL_CR_POWERON or MSR_FSB_FREQ).

Hmm, maybe make it an own driver that creates the sysfs entries somewhere.
I don't think it's useful enough for the main kernel.

But what happens during power saving that may lower the frequency? 
Wouldn't you need update events for that? That might complicate it.

> 
> Don't we already have /sys entries that exits only for certain processors
> or platforms?

Yes.

> I think the Opteron have HYPERTRANSPORT-related events which could be used
> to obtain similar metrics.

Yes, but you usually don't need the frequency.

-Andi
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