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    SubjectRe: [PATCH 3/3 v2] nmi_watchdog: config option to enable new nmi_watchdog

    * Don Zickus <dzickus@redhat.com> wrote:

    > +config NMI_WATCHDOG
    > + bool "Detect Hard Lockups with an NMI Watchdog"
    > + depends on DEBUG_KERNEL && PERF_EVENTS
    > + default y
    > + help
    > + Say Y here to enable the kernel to use the NMI as a watchdog
    > + to detect hard lockups. This is useful when a cpu hangs for no
    > + reason but can still respond to NMIs. A backtrace is displayed
    > + for reviewing and reporting.
    > +
    > + The overhead should be minimal, just an extra NMI every few
    > + seconds.

    Thought for later patches: I think an architecture should be able to express
    via a Kconfig switch that it actually _has_ NMI events. There's architectures
    which dont have a PMU driver and only have software events. There's also
    architectures that have a PMU driver but no NMIs.

    Something like ARCH_HAS_NMI_PERF_EVENTS?

    Also, i havent checked, but what is the practical effect of the new generic
    watchdog on x86 CPUs that does not have a native PMU driver yet - such as
    P4s?

    Anyway, i'll create a tip:perf/nmi topic branch for these patches, it
    certainly looks like a useful generalization and a new architecture that has
    perf could easily enable it, without having to write its own NMI watchdog
    implementation. It's also useful for any new watchdog features that people
    might want to add. Plus it makes the x86 PMU code cleaner in the long run as
    well.

    Thanks,

    Ingo


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