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

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Date:	Fri, 3 Jul 2015 09:42:08 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	"Brown, Len" <len.brown@...el.com>
Cc:	Andy Lutomirski <luto@...capital.net>,
	Prarit Bhargava <prarit@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, X86 ML <x86@...nel.org>,
	"Chandramouli, Dasaratharaman" 
	<dasaratharaman.chandramouli@...el.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	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>
Subject: Re: [PATCH] x86, msr: Allow read access to /dev/cpu/X/msr


* Brown, Len <len.brown@...el.com> wrote:

> > This driver only knows how to handle counters, though.  I'm not sure
> > whether all of the MSRs that turbostat needs are counters.
> 
> turbostat --debug
> dumps a lot of configuration MSRs that are not counters.
>
> "--debug" is not an obscure option, it is the only way that the turbostat is 
> used by advanced users, since it shows not just how fast a system is running, 
> but explains why.

I see no problems there: the main property for perf is read-only access - so it 
will work fine with non-counting MSRs as well.

Really, for system-wide statistics perf is the way to go, it has rich kernel side 
and user side support. We already kind of expose MSRs via the RAPL energy PMU 
bits. All we need is to extend it to an enumerated list of MSRs.

Thanks,

	Ingo
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