Re: [PATCH] perf/x86: check ucode before disabling PEBS onSandyBridge

[Borislav Petkov]

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...

[ â ]

> > +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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