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

From: Aristeu Rozanski
Date: Wed Nov 04 2009 - 10:19:38 EST

> > 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?


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