[RFC] [PATCH] x86: avoid per_cpu for APIC id tables

[Andrew Hunter]

Hi, I have a patch (following) that modifies handling of APIC id tables,
trading a small amount of space in the (NR_CPUS - nr_cpu_ids) >> 0 case for
faster accesses and slightly better cache layout (as APIC ids are mostly used
cross-cpu.)  I'm not an APIC expert so I'd appreciate some eyes on this, but
it shouldn't change any behavior whatsoever.  Thoughts? (We're likely to merge
this internally even if upstream judges the space loss too much of a cost, so
I'd like to know if there's some other problem I've missed that this causes.)

I've tested this cursorily in most of our internal configurations but not in
any particularly exotic hardware/config.