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

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Message-ID: <4FD22228.2030607@zytor.com>
Date:	Fri, 08 Jun 2012 09:02:48 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Borislav Petkov <borislav.petkov@....com>
CC:	Stephane Eranian <eranian@...gle.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
	andi@...stfloor.org, mingo@...e.hu, ming.m.lin@...el.com,
	Andreas Herrmann <andreas.herrmann3@....com>,
	Dimitri Sivanich <sivanich@....com>,
	Dmitry Adamushko <dmitry.adamushko@...il.com>
Subject: Re: [PATCH] perf/x86: check ucode before disabling PEBS on SandyBridge

On 06/08/2012 07:17 AM, Borislav Petkov wrote:
> On Fri, Jun 08, 2012 at 04:03:38PM +0200, Stephane Eranian wrote:
>> On Fri, Jun 8, 2012 at 3:59 PM, Peter Zijlstra <peterz@...radead.org> wrote:
>>> On Fri, 2012-06-08 at 15:51 +0200, Borislav Petkov wrote:
>>>> Provided, of course, newer microcode versions means a
>>>> higher version number.
>>>
>>> Fair enough, I assumed this.. is this true?
>>>
>> I would think so, otherwise it gets even messier!
> 
> Need to get Intel folk to say something here, hpa?
> 

There are some exceptions; but it's good enough for this purpose.

The main exception is that not every revision may be installable on
every CPU; so you might have 0x20, 0x24, 0x28 on one CPU and 0x22, 0x26,
0x2a on another; this only requires caution when you set your bracket
values.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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