linux-kernel - Re: [PATCH] perf/x86: check ucode before disabling PEBS on SandyBridge

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Message-ID: <1339601872.8980.52.camel@twins>
Date:	Wed, 13 Jun 2012 17:37:52 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Borislav Petkov <bp@...64.org>,
	Stephane Eranian <eranian@...gle.com>,
	linux-kernel@...r.kernel.org, andi@...stfloor.org, mingo@...e.hu,
	ming.m.lin@...el.com, "Yu, Fenghua" <fenghua.yu@...el.com>
Subject: Re: [PATCH] perf/x86: check ucode before disabling PEBS on
 SandyBridge

On Wed, 2012-06-13 at 07:00 -0700, H. Peter Anvin wrote:
> On 06/13/2012 01:38 AM, Peter Zijlstra wrote:
> > On Tue, 2012-06-12 at 13:58 -0700, H. Peter Anvin wrote:
> >>  even things like Nehalem + Westmere in the same system
> > 
> > Uhm,.. how well do you expect Linux to run on a franken-system like
> > that? I'm pretty sure perf will malfunction in such a setup.
> > 
> 
> perf might, but I have seen such frankensystems in the field and they
> work (although I haven't seen that particular combo, I have to admit.)

Thing is, if we boot on the wsm, perf could fault the system with
nonexistent MSR accesses, if we boot on the nhm worst is wrong numbers I
think.

I'm not really inclined to 'fix' this.. the best I'm willing to accept
is a patch that would detect this situation and simply disable all
hardware perf support for the platform.
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