x86: Add read_mostly declaration/definition to variables from smp.h

Add "read-mostly" qualifier to the following variables in
smp.h:

 - cpu_sibling_map
 - cpu_core_map
 - cpu_llc_shared_map
 - cpu_llc_id
 - cpu_number
 - x86_cpu_to_apicid
 - x86_bios_cpu_apicid
 - x86_cpu_to_logical_apicid

As long as all the variables above are only written during the
initialization, this change is meant to prevent the false
sharing. More specifically, on vSMP Foundation platform
x86_cpu_to_apicid shared the same internode_cache_line with
frequently written lapic_events.

From the analysis of the first 33 per_cpu variables out of 219
(memories they describe, to be more specific) the 8 have read_mostly
nature (tlb_vector_offset, cpu_loops_per_jiffy, xen_debug_irq, etc.)
and 25 are frequently written (irq_stack_union, gdt_page,
exception_stacks, idt_desc, etc.).

Assuming that the spread of the rest of the per_cpu variables is
similar, identifying the read mostly memories will make more sense
in terms of long-term code maintenance comparing to identifying
frequently written memories.

Signed-off-by: Vlad Zolotarov <[email protected]>
Acked-by: Shai Fultheim <[email protected]>
Cc: Shai Fultheim ([email protected]) <[email protected]>
Cc: [email protected]
Cc: Linus Torvalds <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Link: http://lkml.kernel.org/r/1719258.EYKzE4Zbq5@vlad
Signed-off-by: Ingo Molnar <[email protected]>

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