non reliable nmi

[Peter Pentchev]

On Thu, Sep 04, 2003 at 09:16:23AM -0400, Don Bowman wrote:
> > From: Mike Silbersack [mailto:silby at silby.com]
> > On Thu, 28 Aug 2003, Don Bowman wrote:
> > 
> > > I have machdep.ddb_on_nmi=1.
> > > I can drop into the debugger with the magic
> > > key sequence. However, when i hit the NMI
> > > jumper, i don't always go there. Sometimes
> > > I do.
> > > The system is 4-way SMP [2xHTT xeon processors]
> > > with 4.7.
> > >
> > > Any suggestion on where my NMI might be going?
> > 
> > Is your NMI about 106K in size, and does it have the subjects 
> > "Thank you",
> > "Wicked screensaver" and others?  If so, I think I know where it's
> > going...
> 
> ?
> it was actually a serious question. The nmi header on
> my board goes into the ICH-3 of my chipset, but shorting the
> jumper out doesn't always enter the debugger. It does
> sometimes. If I set the NMI_NOW bit in the ICH-3 I always
> enter the debugger. I was curious if anyone else had seen
> this behaviour.

I haven't kept quite up to date on my x86 hardware lately (read: in
the past five to ten years), but I distinctly remember a time when
everyone referred to x86's NMI as a joke: a non-maskable interrupt that
anyone could mask using a simple CLI instruction.  Not sure if this is
still the case, others would have to say if today's processors still may
get so wedged that a NMI request would simply be ignored.

The other possibility is some kind of kernel mess-up, bad enough that an
NMI does indeed reach the processor, the processor does invoke the NMI
handler, yet the handler (DDB) is quite unable to actually do any useful
work - messed up data structures and such.

G'luck,
Peter

-- 
Peter Pentchev	roam at ringlet.net    roam at sbnd.net    roam at FreeBSD.org
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This sentence no verb.
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