Re: [PATCH 3/6] x86: Convert cpu_sibling_map to be a per cpu variable (v2) (fwd)

[Mike Travis <travis@sgi.com>]

[Sorry, I did not see this message until Christoph forwarded it to me.  I'm
guessing we (SGI) still have a problem with our external spam filter?]

> 
> ---------- Forwarded message ----------
> Date: Fri, 31 Aug 2007 19:49:03 -0700
> From: Andrew Morton <akpm@linux-foundation.org>
> To: travis@sgi.com
> Cc: Andi Kleen <ak@suse.de>, linux-mm@kvack.org, linux-kernel@vger.kernel.org,
>     Christoph Lameter <clameter@sgi.com>
> Subject: Re: [PATCH 3/6] x86: Convert cpu_sibling_map to be a per cpu variable
>     (v2)
> 
> On Fri, 24 Aug 2007 15:26:57 -0700 travis@sgi.com wrote:
> 
>> Convert cpu_sibling_map from a static array sized by NR_CPUS to a
>> per_cpu variable.  This saves sizeof(cpumask_t) * NR unused cpus.
>> Access is mostly from startup and CPU HOTPLUG functions.
> 
> ia64 allmodconfig:
> 
> kernel/sched.c: In function `cpu_to_phys_group':                                                                             kernel/sched.c:5937: error: `per_cpu__cpu_sibling_map' undeclared (first use in this function)                               kernel/sched.c:5937: error: (Each undeclared identifier is reported only once
> kernel/sched.c:5937: error: for each function it appears in.)                                                                kernel/sched.c:5937: warning: type defaults to `int' in declaration of `type name'
> kernel/sched.c:5937: error: invalid type argument of `unary *'                                                               kernel/sched.c: In function `build_sched_domains':                                                                           kernel/sched.c:6172: error: `per_cpu__cpu_sibling_map' undeclared (first use in this function)                               kernel/sched.c:6172: warning: type defaults to `int' in declaration of `type name'                                           kernel/sched.c:6172: error: invalid type argument of `unary *'                                                               kernel/sched.c:6183: warning: type defaults to `int' in declaration of `type name'                                           kernel/sched.c:6183: error: invalid type argument of `unary *'                                                               

I'm thinking that the best approach would be to define a cpu_sibling_map() macro
to handle the cases where cpu_sibling_map is not a per_cpu variable?  Perhaps
something like:

#ifdef CONFIG_SCHED_SMT
#ifndef cpu_sibling_map
#define cpu_sibling_map(cpu)    cpu_sibling_map[cpu]
#endif
#endif

My question though, would include/linux/smp.h be the appropriate place for
the above define?  (That is, if the above approach is the correct one... ;-)

Thanks,
Mike
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