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

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Message-ID: <alpine.DEB.2.02.1402051501240.17670@pianoman.cluster.toy>
Date:	Wed, 5 Feb 2014 15:04:03 -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 02:37:29PM -0500, Vince Weaver wrote:
> > On Wed, 5 Feb 2014, Vince Weaver wrote:
> > 
> > > 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.
> > 
> > I can verify the perfctr code does have a case for PPRO errata 26, but it 
> > only disables things on pentium pros with stepping less than 9.
> 
> The doc said 0xB1, right? Should we keep it at that? Its not like
> there's a lot of PPro machines left out there, so better safe than
> sorry.

mfg steping "sB1" which means processor stepping 9.  See page 15 of the 
document linked in the original patch.

I used to have a Pentium Pro that was apparently affected by this erratum
but not any more.  The oldest machine I test perf stuff on is a 
Pentium II.

Vince
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