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

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Date:	Fri, 8 Jun 2012 16:19:21 +0200
From:	Borislav Petkov <borislav.petkov@....com>
To:	Stephane Eranian <eranian@...gle.com>
CC:	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>,
	Borislav Petkov <borislav.petkov@....com>,
	Dimitri Sivanich <sivanich@....com>,
	Dmitry Adamushko <dmitry.adamushko@...il.com>
Subject: Re: [PATCH] perf/x86: check ucode before disabling PEBS on
 SandyBridge

On Fri, Jun 08, 2012 at 04:07:43PM +0200, Stephane Eranian wrote:
> > The very worst is that it does per-cpu micro-code updates, not machine
> > wide. This results in it being able to have different revisions on
> > different cpus. This in turn makes the below O(n^2) :/
> >
> But it's not like this is a frequent operation either...

Yep, you're only doing it when there's new version from the hw vendor or
when rebooting...

[ … ]

> > +extern struct blocking_notifier_head microcode_notifier;
> > +
> That is a problem because microcode can be compiled as a module.
> When I tried compiling your patch I got undefined for this notifier because
> I have microcode update as a module...

Yes, because it uses request_firmware() and it needs userspace.

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Boris.

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