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    SubjectRe: [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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