linux-kernel - Re: [PATCH] perf,x86,p6: Add userspace RDPMC quirk for P6

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Message-ID: <alpine.DEB.2.02.1402051427210.16596@pianoman.cluster.toy>
Date:	Wed, 5 Feb 2014 14:29:36 -0500 (EST)
From:	Vince Weaver <vince@...ter.net>
To:	Peter Zijlstra <peterz@...radead.org>
cc:	junk@...af.co.uk, alan@...rguk.ukuu.org.uk,
	Ingo Molnar <mingo@...nel.org>,
	Stephane Eranian <eranian@...gle.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf,x86,p6: Add userspace RDPMC quirk for P6

On Wed, 5 Feb 2014, Peter Zijlstra wrote:

> On Wed, Feb 05, 2014 at 02:16:43PM -0500, Vince Weaver wrote:
> > On Wed, 5 Feb 2014, Peter Zijlstra wrote:
> > 
> > > P6 class machines can die hard when PCE gets enabled due to CPU
> > > errata. The safe way it so disable it by default and keep it disabled.
> > > 
> > > See errata 26:
> > 
> > so you take an errata applicable to a subset of Pentium Pro steppings and 
> > apply it to the whole p6 line (which includes the whole way up to Pentium 
> > III)?
> > 
> > Or am I missing something in the documentation you link to?
> 
> I forgot it went all the way to P-III, let me try and find the other
> erratas.

from the document you linked it looks like it was fixed by the Pentium 
Pro stepping sB1 (6.1.9).

Has someone actually hit this bug?  People used PAPI/perfctr on these 
machines for years, and it uses rdpmc by default so I would think it would 
show up if it were an issue.  I should check the perfctr code to see if it 
had some sort of check.

Vince
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