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

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Message-ID: <20130517103600.GG8356@rric.localhost>
Date:	Fri, 17 May 2013 12:36:00 +0200
From:	Robert Richter <rric@...nel.org>
To:	Borislav Petkov <bp@...en8.de>
Cc:	Peter Zijlstra <peterz@...radead.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 17.05.13 11:45:51, Borislav Petkov wrote:
> On Fri, May 17, 2013 at 11:27:41AM +0200, Peter Zijlstra wrote:
> > But not all x86 hardware even has the stuff enumerated in CPUID, and
> > afaict Intel and AMD use a different CPUID bit as well, so what's
> > init_hw_perf_events() to do?
> 
> Yeah, I think the best solution would be if we force-enable the CPUID
> bit on F10h very early and teach amd_pmu_init() to look at it. I even
> had a patch which does something like that. I could dust it off and give
> it a try... I just hope we can actually enable a reserved bit in CPUID.

The cpuid bit indicates perfctrs that do not exist, this will setup a
wrong msr range on f10h. I guess the warning is harmless and the code
works properly, but I can't tell for sure now and need to look at it.

Also, the problem occurs on f15h there *no* core perfctrs exist but
are expected, not on a f10h system.

-Robert
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