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    SubjectRe: [PATCH 2/2] x86: introduce NMI_AUTO as nmi_watchdog option

    * Aristeu Rozanski <> wrote:

    > > > NMI_AUTO is a new nmi_watchdog option that makes LAPIC be tried first
    > > > and if the CPU isn't supported, IOAPIC will be used. It's useful in
    > > > cases where NMI watchdog is enabled by default in a kernel built for
    > > > different machines. It can be configured by default or selected with
    > > > nmi_watchdog=3 or nmi_watchdog=auto parameters.
    > >
    > > What i'd like to see for the NMI watchdog is much more ambitious than
    > > this: the use of perf events to run a periodic NMI callback.
    > >
    > > The NMI watchdog would cause the creation of a per-cpu perf_event
    > > structure (in-kernel). All x86 CPUs that have perf event support (the
    > > majority of them) will thus be able to have an NMI watchdog using a
    > > nice, generic piece of code and we'd be able to phase out the open-coded
    > > NMI watchdog code.
    > >
    > > The user would not notice much from this: we'd still have the
    > > /proc/sys/kernel/nmi_watchdog toggle to turn it on/off, and we'd still
    > > have the nmi_watchog= boot parameter as well. But the underlying
    > > implementation would be far more generic and far more usable than the
    > > current code.
    > >
    > > Would you be interested in moving the NMI watchdog code in this
    > > direction? Most of the perf events changes (callbacks, helpers for
    > > in-kernel event allocations, etc.) are in latest -tip already, so you
    > > could use that as a base.
    > but that would work only for LAPIC. You're suggesting killing IOAPIC
    > mode too?

    Would it be a big loss, with all modern systems expected to have a
    working lapic based NMI source? I wrote the IOAPIC mode originally but i
    dont feel too attached to it ;-)


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