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

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Date:	Fri, 30 Mar 2007 14:44:39 -0400
From:	Martin Cracauer <cracauer@...s.org>
To:	Stephane Eranian <eranian@....hp.com>
Cc:	linux-kernel@...r.kernel.org, perfmon@...ali.hpl.hp.com
Subject: Re: [perfmon] exposing FSB clock speed in /sys

Stephane Eranian wrote on Fri, Mar 30, 2007 at 07:39:37AM -0800: 
> Hello,
> 
> It seems that the kernel does not expose the Front-Side Bus (FSN) Clock
> speed to user applications. I found code in the kernel dealing with
> frequency scaling that extracts the information for x86 processors but
> the value is never exposed.
> 
> Knowledge the the FSB speed is very useful to monitoring tools. It is used
> to compute certain bus-related metrics.
> 
> Looking at the code, it seems that there is no standard way of extracting
> the FSB speed. For each processor model, you have different MSRs. I would
> think that the routines in the cpufreq code could be moved out and used
> as the basis to expose the information somewhere in /sys.

That is still problematic as finding out the FSB might not be
trivial.  For example, for the NForce4 chipsets we have a too to
manipulate FSB and multipliers, but it's not in the kernel and never
will be.  I don't think that K8 has a way to find the FSB from the CPU
only, so you are bound to tangle with "nice" chipsets from NVidia et al.

I like the idea, but I expect there will be reservations against
presenting a /proc file that cannot be supported for almost all
machines. 

In general, I would like the cpufreq code split up, as I need to reuse
parts of it for other clock manipulation projects.  Currently, cpufreq
is a blob of code to manipulate frequencies, and to deal with the
fallout.  These two should be split up.

Martin
-- 
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
Martin Cracauer <cracauer@...s.org>   http://www.cons.org/cracauer/
FreeBSD - where you want to go, today.      http://www.freebsd.org/
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