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

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Message-ID: <55929834.8090800@redhat.com>
Date:	Tue, 30 Jun 2015 09:23:00 -0400
From:	Prarit Bhargava <prarit@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
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 06/30/2015 08:44 AM, Peter Zijlstra wrote:
> 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.
> 

Yes, I agree.

> 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.

Yep, that was my plan -- I'm going to do the in-tree utilities first then look
at the external programs.

> 
> 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.
> 

Thanks Peter!

P.
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