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

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Date:	Fri, 8 Jun 2012 12:03:49 +0200
From:	Stephane Eranian <eranian@...gle.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
	andi@...stfloor.org, mingo@...e.hu, ming.m.lin@...el.com
Subject: Re: [PATCH] perf/x86: check ucode before disabling PEBS on SandyBridge

On Fri, Jun 8, 2012 at 12:00 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Fri, 2012-06-08 at 11:35 +0200, Ingo Molnar wrote:
>> * Peter Zijlstra <peterz@...radead.org> wrote:
>>
>> > On Thu, 2012-06-07 at 12:48 +0200, Stephane Eranian wrote:
>> > > >> The warning could also be done on boot. But the check has to be done
>> > > >>  when the event is created.
>> > > >
>> > > > Is this because of the ucode loader not having done its thing yet etc..?
>> >
>> > Ah, its because you can update ucode at runtime of course.
>> >
>> > A quick look at the ucode loader doesn't show it having a
>> > notifier either, so then yeah we need to check on every event
>> > creation :/
>> >
>> > Or we could put a hook in the ucode loader.
>>
>> I'd really suggest the latter - I doubt this will be our only
>> ucode dependent quirk, going forward ...
>
> Yeah, am in the middle of writing that..

I am fine with that. As I found out yesterday, the reality is that the
ucode version for SNB vs. SNB-EP differ, so with this mechanism
we could customize the callback per CPU model number more easily.
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