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 10:23:20 -0800
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On Wed, 2007-02-21 at 19:18 +0100, Thomas Gleixner wrote:
> On Wed, 2007-02-21 at 09:38 -0800, Daniel Walker wrote:
> > > > 
> > > > Could be the switch over then which confuses the NMI . 
> > > 
> > > Why? The switch just stops the PIT/HPET. It does not fiddle with IO_APIC
> > > and friends at all.
> > 
> > I'm not an expert on the io-apic, but the check_timer() function seemed
> > to assume IRQ0 was happening regularly ..
> 
> Again: 
> 
> check_timer() is called _BEFORE_ we even touch the local APIC timers. At
> this point PIT/HPET _IS_ firing IRQ0 with HZ frequency.

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? 

> > Well, I'm pretty sure it's HRT, cause in prior versions this only
> > happened when HRT is enabled. Then you guys went to the lapic all the
> > time, and now this is happening all the time ..
> 
> The NMI is stuck:
> 
>                 if (nmi_count(cpu) - prev_nmi_count[cpu] <= 5) {
>                         printk("CPU#%d: NMI appears to be stuck (%d->%d)!\n",
>                                 cpu,
>                                 prev_nmi_count[cpu],
>                                 nmi_count(cpu));
> 
> This has nothing to do with jiffies.

I think it has to do with IRQ0 . Did I mention this doesn't happen in
2.6.20 .

> There have been a bunch of changes in arch/i386/kernel/nmi.c as well. 
> 
> > You can't reproduce this?
> 
> Nope.

Do you use nmi_watchdog=1 ?

Daniel

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