Subject: Re: [Fastboot] [PATCH] Fix interrupt distribution in ppc970

From: Vivek Goyal <[email-masked]>
Date: Wed, 7 Mar 2007 11:36:23 +0530

On Tue, Mar 06, 2007 at 03:16:55PM +0100, Michael Ellerman wrote:
> On Tue, 2007-03-06 at 19:27 +0530, Mohan Kumar M wrote:
> > Hi,
> > 
> > Here comes the revised version of patch to fix the interrupt missing
> > problem when a kdump kernel is booted with "maxcpus=1" kernel parameter.
> > 
> > In the xics initialization code a check is made to detemine whether
> > maxcpus kernel parameter is present and if its present then
> > default_distrib_server variable is initialized to the current boot cpu
> > id (by default_server variable). So that when ever a kernel is booted
> > with maxcpus kernel parameter all interrupts are routed to the boot cpu
> > only.
> > 
> > Tested on POWER5 and JS20 systems.
> 
> First, I don't know why we keep telling people to use maxcpus=1 for
> kexec/kdump - it's causing bugs, and I don't know of any that it fixes?
> 

Logically speaking, there is no need to bring up all the cpus in the
system to capture the dump. A single cpu can do the job, may be in
relatively lesser memory. Just because we see bugs with maxcpus=1, does
not mean we should try to bring up all the cpus in second kernel. I think
we should try to clean maxcpus=1 path instead.

Thanks
Vivek