Re: [PATCH v4 0/3] x86, apic, kexec: Add disable_cpu_apic kernel parameter

Vivek Goyal
2013-10-23T15:53:27Z

On Wed, Oct 23, 2013 at 09:05:06AM +0900, HATAYAMA Daisuke wrote:

[..]
> >Do you literally mean a human at each boot will have to configure
> >the kdump configuration files for passing disable_cpu_apic?
> >Or do you envision the setting of disable_cpu_apic being put into
> >the kdump initialization scripts?
> >
> >thanks
> >
> >Jerry
>
> Nearer to the former case, but this is not what a human should do. It's
> a cumbersome task. I think, on fedora/RHEL system for example, kdump
> service should check at each boot automatically.

Hi Hatayama,

So what information should I look for to prepare disable_cpu_apic=X in
kdump script?

Is BSP processor info exported to user space somewhere? Or assuming that
processor 0 is BSP and corresponding apicid should be disabled in kdump
kernel is good enough?

I am looking at /proc/cpuinfo and following 3 fields seem interesting.

processor: 0
apicid : 0
initial apicid : 0

What's the difference between apicid and "initial apicid". I guess
initial apicid reflects the apicid number as set by firmware and then
kernel can overwrite it and new number would be reflected in "apicid"?

If that's the case, then I guess we should be looking at "apicid" of
processor "0" and set that in disable_cpu_apic? Because that's the
number kdump kernel boot should see in apic upon boot.

Thanks
Vivek