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

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Message-ID: <m1sl2oa1ev.fsf@ebiederm.dsl.xmission.com>
Date:	Thu, 29 Nov 2007 19:54:16 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Ben Woodard <woodard@...hat.com>
Cc:	Vivek Goyal <vgoyal@...hat.com>, Neil Horman <nhorman@...hat.com>,
	kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Andi Kleen <ak@...e.de>, hbabu@...ibm.com,
	Andi Kleen <andi@...stfloor.org>
Subject: Re: [PATCH] kexec: force x86_64 arches to boot kdump kernels on boot cpu

Ben Woodard <woodard@...hat.com> writes:

> 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.
>>
>> 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.
>>
>
> Neil whipped up a patch to try this and evidently it worked on his test boxes
> but it didn't work very well on our problem tests box. It hung after the kernel
> printed "Ready". i.e. on a normal boot I get:

Interesting can you please try an early_printk console.


I expect you made it a fair ways and it just didn't show up because you didn't
get as far as the normal serial port setup.

You don't have any output from your linux kernel.

Eric
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