Re: [PATCH RFC 0/5] hard_smp_processor_id overhaul

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On Thu, 2007-03-01 at 09:06 -0500, Benjamin LaHaise wrote:
> On Thu, Mar 01, 2007 at 04:16:13PM +0900, Fernando Luis Vázquez Cao wrote:
> > As a consequence, the hardcoding of hard_smp_processor_id() to 0 on UP
> > systems (see "linux/smp.h") is not correct.
> > 
> > This patch-set does the following:
> > 
> > 1- Remove hardcoding of hard_smp_processor_id on UP systems.
> NAK.  This has to be configurable, as many embedded systems don't even 
> have APICs.  Please rework the patch set so that there is not any overhead 
> for existing UP systems.
In i386 (with the exception of voyager) and x86_64,
hard_smp_processor_id is not used anywhere in the kernel when there are
no APICs available.

Regarding the overhead, hard_smp_processor_id is used mostly during
initialization and doesn't seem to be used in any fast path in i386,
x86_64, and ia64. All the other architectures are not affected by this
patch, because I kept the hardcoding of hard_smp_processor_id on UP
kernels, and just moved the definition to asm/smp.h because it should be
handled by architecture-speficic code.

So unless strictly necessary I would not like to make this patches
dependent on kdump.

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