linux-kernel - Re: [PATCH 2/2] x86: introduce NMI_AUTO as nmi

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Message-ID: <20091104151929.GH18613@redhat.com>
Date:	Wed, 4 Nov 2009 10:19:29 -0500
From:	Aristeu Rozanski <aris@...hat.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] x86: introduce NMI_AUTO as nmi_watchdog option

> > 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?

-- 
Aristeu

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