linux-kernel - Re: [PATCH v4 0/3] x86, apic, kexec: Add disable_cpu

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Date:	Wed, 23 Oct 2013 11:51:27 -0400
From:	Vivek Goyal <vgoyal@...hat.com>
To:	HATAYAMA Daisuke <d.hatayama@...fujitsu.com>
Cc:	jerry.hoemann@...com, hpa@...ux.intel.com, ebiederm@...ssion.com,
	kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
	bp@...en8.de, akpm@...ux-foundation.org, fengguang.wu@...el.com,
	jingbai.ma@...com
Subject: Re: [PATCH v4 0/3] x86, apic, kexec: Add disable_cpu_apic kernel
 parameter

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
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