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Date: Tue, 10 Nov 2009 06:20:51 +0100 From: Ingo Molnar <mingo@...e.hu> To: Aristeu Rozanski <aris@...hat.com> Cc: Thomas Gleixner <tglx@...utronix.de>, "H. Peter Anvin" <hpa@...or.com>, Peter Zijlstra <a.p.zijlstra@...llo.nl>, Fr?d?ric Weisbecker <fweisbec@...il.com>, linux-kernel@...r.kernel.org Subject: Re: [PATCH 2/2] x86: introduce NMI_AUTO as nmi_watchdog option * Aristeu Rozanski <aris@...hat.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 ;-) > > ok, fair enough. but since it'll be another implementation, do you > mind applying the patches I submitted so they can be used until the > new implementation is in place? For that i need to see at least an RFC v1 version series of the new implementation - otherwise we might end up sitting on this interim version with no-one doing the better variant. Thanks, Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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