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    SubjectRe: [PATCH] perf/x86: check ucode before disabling PEBS on SandyBridge
    On Tue, 2012-06-12 at 19:09 +0200, Stephane Eranian wrote:
    > > Instead of registering a microcode notifier, why not checking the
    > > availability of pebs dynamically with each syscall in
    > > intel_pmu_hw_config()? It looks like intel_snb_verify_ucode() is not
    > > that much expensive. We can perform the check only if the event
    > could
    > > be for pebs and if pebs is broken. The check could be repeated when
    > > setting up a new event after ucode could potentially has been
    > updated
    > > (e.g. after bringing a cpu online or so).

    Because you then end up with a for_each_online_cpu() loop in there,
    that's not pretty and quite horrible on large systems when you need to
    create nr_cpus events.

    Furthermore, ucode update is the rare thing, creating events happens
    much more frequently.

    > That's what I had in my original version.

    Right, but you really need to check all cpus, not just the one you
    happen to run on or the boot cpu.

     \ /
      Last update: 2012-06-13 00:03    [W:0.026 / U:18.944 seconds]
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