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

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Message-ID: <4FD7AD6F.6010008@zytor.com>
Date:	Tue, 12 Jun 2012 13:58:23 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Borislav Petkov <bp@...64.org>
CC:	Peter Zijlstra <peterz@...radead.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 06/12/2012 01:56 PM, Borislav Petkov wrote:
> On Tue, Jun 12, 2012 at 01:42:07PM -0700, H. Peter Anvin wrote:
>> I personally don't know of any valid use case for per-core loads, and
>> it sounds like a horrid idea.
> 
> Vehemently agreed.
> 
> However, last time we talked about Ingo mentioned some possibility
> of having different microcode versions on different CPUs:
> http://lkml.indiana.edu/hypermail/linux/kernel/1105.3/00749.html
> 
> Hmm...
> 
>> And yes, I would prefer a single sysfs file, or better yet a plain old
>> device node.
> 
> Also agreed.
> 

There is a difference here.  Mixed steppings or even mixed CPUs are,
indeed, supported (even things like Nehalem + Westmere in the same
system).  However, the notion is that we should upload the *entire set*
of microcodes to the kernel, and let it flash the appropriate one into
each CPU.

This may result in different version number on different CPUs.

	-hpa
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