Re: [PATCH 03/12] x86-64: Convert irqstacks to per-cpu

[Brian Gerst <brgerst@gmail.com>]

On Sun, Jan 18, 2009 at 11:39 AM, Tejun Heo <tj@kernel.org> wrote:
> From: Brian Gerst <brgerst@gmail.com>
>
> Move the irqstackptr variable from the PDA to per-cpu.  Make the
> stacks themselves per-cpu, removing some specific allocation code.
> Add a seperate flag (is_boot_cpu) to simplify the per-cpu boot
> adjustments.
>
> tj: * sprinkle some underbars around.
>
>    * irq_stack_ptr is not used till traps_init(), no reason to
>      initialize it early.  On SMP, just leaving it NULL till proper
>      initialization in setup_per_cpu_areas() works.  Dropped
>      is_boot_cpu and early irq_stack_ptr initialization.

And it adds more #ifdefs.  All these conditional initializations on
CONFIG_SMP are really cluttering up the code.  It also conflicts with
one of my goals with these patches: have as much state as possible
already prepared when a cpu boots.  For the boot cpu this means static
initialization.  For secondary cpus, that means setting up the values
in setup_per_cpu_areas().  This eliminates any window where the state
isn't ready yet, as you've already seen with per_cpu_offset.

And is_boot_cpu was a worthwhile optimization on its own.  I had plans
on using it in more places later.

--
Brian Gerst