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

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Message-ID: <20071128210944.GA28236@hmsendeavour.rdu.redhat.com>
Date:	Wed, 28 Nov 2007 16:09:44 -0500
From:	Neil Horman <nhorman@...hat.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Vivek Goyal <vgoyal@...hat.com>, 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

On Wed, Nov 28, 2007 at 12:42:22PM -0700, Eric W. Biederman wrote:
> 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.
> 

http://www.hypertransport.org/docs/tech/HTC20051222-0046-0008-Final-4-21-06.pdf
Table 143 suggest to me that legacy interrupts should be routed to all cpus,
which certainly doesn't seem to be the case in this situation.  Perhaps Nvidia
goofed on that part of the specification?


> 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.
> 
Certainly, this seems like the best solution long term.

So I'm looking at the implementation for 64 bit system, and it seems a little
cleaner than 32 bit setup.  I'm wondering if we can just call setup_IO_APIC
immediately after init_IRQ in start_kernel?  Could it be that straightforward?

Neil

> Eric

-- 
/***************************************************
 *Neil Horman
 *Software Engineer
 *Red Hat, Inc.
 *nhorman@...hat.com
 *gpg keyid: 1024D / 0x92A74FA1
 *http://pgp.mit.edu
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