linux-kernel - Re: [PATCH] x86, msr: Allow read access to /dev/cpu/X/msr

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Message-ID: <20150630124426.GD12596@twins.programming.kicks-ass.net>
Date:	Tue, 30 Jun 2015 14:44:26 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Prarit Bhargava <prarit@...hat.com>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Andy Lutomirski <luto@...capital.net>,
	Ingo Molnar <mingo@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, X86 ML <x86@...nel.org>,
	Len Brown <len.brown@...el.com>,
	Dasaratharaman Chandramouli 
	<dasaratharaman.chandramouli@...el.com>,
	Borislav Petkov <bp@...en8.de>,
	Andy Lutomirski <luto@...nel.org>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Brian Gerst <brgerst@...il.com>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Henrique de Moraes Holschuh <hmh@....eng.br>,
	Matt Fleming <matt@...eblueprint.co.uk>
Subject: Re: [PATCH] x86, msr: Allow read access to /dev/cpu/X/msr

On Tue, Jun 30, 2015 at 08:20:55AM -0400, Prarit Bhargava wrote:
> it seems like visiting changes on each of these packages (and the other
> packages that I'm sure I've missed) will be moderately difficult.
> 
> Thoughts?

Start by changing the ones users want to run most and leave the rest
requiring root privs until someone has the time to convert them.

Its not like we can remove the msr driver any time soon anyway.

So I would suggest starting with the perf MSR driver thingy for all
those MSRs that count things and see if you can convert say
turbostat/cpufrequtils/powertop over to that.

I suspect there's MSR that are useful to expose but are not counting,
I'm not sure perf is the right interface for those.

Making an inventory on which MSRs are required by these tools and what
kind of data they provide might give a good idea on how to continue.

If most of these tools only use counting MSRs that can be serviced with
the perf-msr driver then that would be great.
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