Subject: Re: Linux 2.6.21-rc1
From: Daniel Walker <dwalker@mvista.com>
To: tglx@linutronix.de
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, mingo@elte.hu
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Date: Wed, 21 Feb 2007 11:24:56 -0800
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On Wed, 2007-02-21 at 20:23 +0100, Thomas Gleixner wrote:
> On Wed, 2007-02-21 at 10:23 -0800, Daniel Walker wrote:
> > Right, but eventually there isn't a regular timer interrupt through the
> > io-apic. I don't think in the past IRQ0 stops without the system
> > crashing, so check_timer() could assume the timer (IRQ0) is _always_
> > regular.
> > 
> > do you know what the requirement are for routing the NMI through the
> > io-apic? 
> 
> Sorry. I checked. switching PIT off really breaks nmi_watchdog=1, as
> this just mirrors IRQ#0 to the NMI. No IRQ#0 from PIT, no NMI

That's what I suspected ..

> We could keep PIT running with an empty interrupt handler when
> nmi_watchdog=1 is set, but this interferes nicely with broadcasting.
> 
> Does nmi_watchdog=2 work ? We might switch to that, when a local APIC is
> available. 

Oddly, nmi_watchdog=2 doesn't work in 2.6.21-rc1, but it works in
2.6.20-rt8 however I'm not sure of the config could have been PREEMPT_RT
was on.

Daniel

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