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    SubjectRe: [patch] disable NMI watchdog by default
    From
    Date
     > --- linux.orig/include/asm-x86_64/nmi.h
    > +++ linux/include/asm-x86_64/nmi.h
    > @@ -63,7 +63,7 @@ extern int setup_nmi_watchdog(char *);
    >
    > extern atomic_t nmi_active;
    > extern unsigned int nmi_watchdog;
    > -#define NMI_DEFAULT -1
    > +#define NMI_DEFAULT 0

    Maybe I'm missing something obvious, but this patch doesn't seem
    correct to me. The sentiment of disabling the NMI watchdog by default
    is fine, and I agree with it, but I don't think this patch does what
    it says. First of all, I have a system running a kernel with this
    patch applied (v2.6.21-rc2-gc3442e2), and I see NMIs in
    /proc/interrupts and "testing NMI watchdog ... OK." in the log.

    And second, looking at the NMI code, it seems that this change
    actually makes it impossible to turn off the NMI watchdog! In
    arch/x86_64/kernel/nmi.c, we have:

    void nmi_watchdog_default(void)
    {
    if (nmi_watchdog != NMI_DEFAULT)
    return;
    if (nmi_known_cpu())
    nmi_watchdog = NMI_LOCAL_APIC;
    else
    nmi_watchdog = NMI_IO_APIC;
    }

    so it seems changing the value of NMI_DEFAULT has no effect on this
    logic, really: if nmi_watchdog is left at the default, then the kernel
    chooses LAPIC or IO-APIC. And if someone passes "nmi_watchdog=0" on
    the command line, nmi_watchdog is still NMI_DEFAULT and so the same
    logic triggers.

    Ingo, I assume you tested this, so what am I missing?

    - R.
    -
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