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    SubjectRe: Linux 2.6.21-rc5

    On Wed, 28 Mar 2007, Andi Kleen wrote:
    > Can you test this patch please?

    This patch is totally broken.

    > i386/x86-64: Convert nmi reservation to be global
    > It doesn't make much sense to have this per CPU, because all
    > the services using NMIs run on all CPUs. So make it global.


    If you do this, then you must make all *callers* be global too. But they
    aren't. Right now all callers do per-CPU setup!

    See for example enable_lapic_nmi_watchdog():

    on_each_cpu(setup_apic_nmi_watchdog, NULL, 0, 1);

    where "setup_apic_nmi_watchdog()" will call "setup_k7_watchdog()", which
    in turn will do a per-CPU reservation of the perfctl for the watchdog.

    So I agree in that it probably doesn't make sense to have NMI/perfctl
    reservation per-CPU, but you can't just change the reservation and ignore
    all the *users* of that reservation that assumed that it was per-CPU.

    Is that code insane? Probably. But it probably also works. After your
    patch, one CPU will be able to reserve the NMI/perfctl thing (fine so far)
    but then all the other CPU's that try to do it will fail.

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      Last update: 2007-03-28 19:59    [W:0.021 / U:8.808 seconds]
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