linux-kernel - Re: [PATCH] kexec: force x86_64 arches to boot kdump kernels on boot cpu

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Date:	Wed, 28 Nov 2007 12:42:22 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	Neil Horman <nhorman@...hat.com>, Ben Woodard <woodard@...hat.com>,
	Andi Kleen <andi@...stfloor.org>, kexec@...ts.infradead.org,
	linux-kernel@...r.kernel.org, Andi Kleen <ak@...e.de>,
	hbabu@...ibm.com
Subject: Re: [PATCH] kexec: force x86_64 arches to boot kdump kernels on boot cpu

Vivek Goyal <vgoyal@...hat.com> writes:

> Ok. Got it. So in this case we route the interrupts directly through LAPIC
> and put LVT0 in ExtInt mode and IOAPIC is bypassed.
>
> I am looking at Intel Multiprocessor specification v1.4 and as per figure
> 3-3 on page 3-9, 8259 is connected to LINTIN0 line, which in turn is 
> connected to LINTIN0 pin on all processors. If that is the case, even in
> this mode, all the CPU should see the timer interrupts (which is coming
> from 8259)?

However things are implemented completely differently now.  I don't think
the coherent hypertransport domain of AMD processors actually routes
ExtINT interrupts to all cpus but instead one (the default route?) is
picked.

So I think for the kdump case we pretty much need to use an IOAPIC
in virtual wire mode for recent AMD systems.

For current Intel systems I believe either scenario still works.

> Can you print the LAPIC registers (print_local_APIC) during normal boot
> and during kdump boot and paste here?

It's worth a look.

I still think we need to just use apic mode at kernel startup, and
be done with it.

Eric
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