[RESEND PATCH v10] x86, apic, kexec, Documentation: Add disable_cpu_apicid kernel parameter

H. Peter Anvin hpa at zytor.com
Wed Jan 15 12:54:31 EST 2014

On 01/15/2014 09:47 AM, Vivek Goyal wrote:
> On Wed, Jan 15, 2014 at 09:26:14AM -0800, H. Peter Anvin wrote:
>> On 01/15/2014 09:05 AM, Vivek Goyal wrote:
>>> I think this is a reasonable approach to solve the issue. Use a command
>>> line to not bring up specific cpu in second kernel which can create
>>> problems.
>>> Acked-by: Vivek Goyal <vgoyal at redhat.com>
>>> hpa, I know you are not excited about this approach. If you made up your
>>> mind that this appoarch is not worth pursuing, please do suggest what
>>> would you like to see and we can give that a try.
>>> We want to solve this problem as on large memory machines saving dump can
>>> take lot of time and we want to bring up multiple cpus and speed up
>>> compression and save on dump time.
>> I'm not excited about kdump's reliance on the command line, since it
>> seems to be a neverending source of trouble, simply because the command
>> line is fundamentally intended as a human interface.
> So in general, what are the alternatives? Either we figure out that kernel
> is booting as kdump kernel and do things differently. That seems even
> worse as what do we want in kdump kernel will change over a period of
> time.
> Other thing is that pass more information in bootparams. But that does
> not seem much different than command line to me.

It is the commingling of semantics that is the problem.  Command line
options are generally imperative, "do this".  What you want in the kdump
situation, as you yourself state above, is get a description of the
current situation and let the kdump side choose the action to take.

As a transport mechanism the command line suffers from limited size and
that you have to share it with an arbitrary amount of user-provided
options that may or may not be essential.

>>  However, this
>> seems relatively harmless in comparison with everything else and I am
>> much happier with saving the ID in the first kernel rather than trying
>> to guess if a currently-downed CPU is the BSP.
> So looks like you are alright with this patch. Can you please queue it
> up in your tree.

In process.


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