linux-kernel - Re: Drop WARN on AMD lack of perfctrs

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Message-ID: <20130517090451.GQ19669@dyad.programming.kicks-ass.net>
Date:	Fri, 17 May 2013 11:04:51 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Borislav Petkov <bp@...en8.de>
Cc:	Robert Richter <rric@...nel.org>, Josh Boyer <jwboyer@...hat.com>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	x86@...nel.org, linux-kernel@...r.kernel.org, gleb@...hat.com
Subject: Re: Drop WARN on AMD lack of perfctrs

On Thu, May 16, 2013 at 11:34:20PM +0200, Borislav Petkov wrote:
> On Thu, May 16, 2013 at 10:55:58PM +0200, Robert Richter wrote:
> > iirc the reason was the different msr range that is switched on fam15h
> > with a different counter to counter msr offset of 2 instead of 1. The
> > code relies on the assumption that the msrs exist on that cpu. Thus
> > the warning if not. Also note that code may have changed in 3.10 in
> > that area.
> 
> Stupid question: why is check_hw_exists() *after* the vendor-specific
> counter detection code in init_hw_perf_events() even though it is
> supposed to check whether hardware is emulated?

Mostly so that check_hw_exists() doesn't need to know about the vendor
specifics like where the MSRs live, how many there are etc..


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