Re: [rfc] fix Kconfig, hotplug_cpu is needed for swsusp

[Andrew Morton <akpm@osdl.org>]

Ashok Raj <ashok.raj@intel.com> wrote:
>
> On Wed, Mar 29, 2006 at 02:47:46PM -0800, Andrew Morton wrote:
>  > Pavel Machek <pavel@ucw.cz> wrote:
>  > >
>  > > HOTPLUG_CPU is needed on normal PCs, too -- it is neccessary for
>  > > software suspend.
>  > > 
>  > 
>  > OK, this will get ugly.  APICs are involved.
> 
>  I guess you need only on systems that support >1 cpu right? I doubt you will need
>  it on a system that cannot run with the config-generic-arch on. although we use bigsmp 
>  when hotplug is turned on, all we really end up is using flat physical mode instead
>  of using logical mode.
> 
>  I still havent understood why this wont work. Choosing CONFIG_X86_GENERICARCH shouldnt
>  break anything AFAICT.
> 
>  Pavel, you could use CONFIG_HOTPLUG_CPU, just need to enable X86_GENERICARCH now. 
>  Is there a reason you think that wont work? I wish we would revert it for a strong 
>  reason that we know will not make hotplug work on certain systems because of this choise
>  not that we currently have X86_PC now, and are unwiling to change the config.
> 
>  (PS: the word bigsmp although sounds like some large NR_CPUS, its just using a mode that
>  permits the system to work from 1 .. >8 cpus. So there is really nothing determental 
>  to selecting this.)

Something which remains to be beaten into my head: *why* does HOTPLUG_CPU
require flat pyhsical mode?  What necessitated that change, and cannot we
make it work OK in logical mode as well as flat mode?
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