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

* Aristeu Rozanski <aris@redhat.com> 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 ;-)

Ingo


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