• Vlad Zolotarov's avatar
    x86: Add read_mostly declaration/definition to variables from smp.h · 0816b0f0
    Vlad Zolotarov authored
    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: default avatarVlad Zolotarov <vlad@scalemp.com>
    Acked-by: default avatarShai Fultheim <shai@scalemp.com>
    Cc: Shai Fultheim (Shai@ScaleMP.com) <Shai@scalemp.com>
    Cc: ido@wizery.com
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Andrew Morton <akpm@linux-foundation.org>
    Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
    Link: http://lkml.kernel.org/r/1719258.EYKzE4Zbq5@vladSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
    0816b0f0
setup_percpu.c 7.93 KB