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Date: Fri, 8 Jun 2012 16:19:21 +0200
From: Borislav Petkov <borislav.petkov@amd.com>
To: Stephane Eranian <eranian@google.com>
CC: Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@kernel.org>,
        <linux-kernel@vger.kernel.org>, <andi@firstfloor.org>, <mingo@elte.hu>,
        <ming.m.lin@intel.com>, Andreas Herrmann <andreas.herrmann3@amd.com>,
        Borislav Petkov <borislav.petkov@amd.com>,
        Dimitri Sivanich <sivanich@sgi.com>,
        Dmitry Adamushko <dmitry.adamushko@gmail.com>
Subject: Re: [PATCH] perf/x86: check ucode before disabling PEBS on
 SandyBridge
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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.

-- 
Regards/Gruss,
Boris.

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