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    Subject[tip:x86/mm] x86: Add read_mostly declaration/ definition to variables from smp.h
    Commit-ID:  0816b0f0365539c8f6280634d2c1778d0108d8f5
    Gitweb: http://git.kernel.org/tip/0816b0f0365539c8f6280634d2c1778d0108d8f5
    Author: Vlad Zolotarov <vlad@scalemp.com>
    AuthorDate: Mon, 11 Jun 2012 12:56:52 +0300
    Committer: Ingo Molnar <mingo@kernel.org>
    CommitDate: Thu, 14 Jun 2012 12:42:11 +0200

    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 <vlad@scalemp.com>
    Acked-by: Shai 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@vlad
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    ---
    arch/x86/include/asm/apic.h | 2 +-
    arch/x86/include/asm/smp.h | 16 ++++++++--------
    arch/x86/kernel/apic/apic.c | 6 +++---
    arch/x86/kernel/setup_percpu.c | 2 +-
    arch/x86/kernel/smpboot.c | 8 ++++----
    5 files changed, 17 insertions(+), 17 deletions(-)

    diff --git a/arch/x86/include/asm/apic.h b/arch/x86/include/asm/apic.h
    index eaff479..a907d4d 100644
    --- a/arch/x86/include/asm/apic.h
    +++ b/arch/x86/include/asm/apic.h
    @@ -537,7 +537,7 @@ static inline const struct cpumask *default_target_cpus(void)
    #endif
    }

    -DECLARE_EARLY_PER_CPU(u16, x86_bios_cpu_apicid);
    +DECLARE_EARLY_PER_CPU_READ_MOSTLY(u16, x86_bios_cpu_apicid);


    static inline unsigned int read_apic_id(void)
    diff --git a/arch/x86/include/asm/smp.h b/arch/x86/include/asm/smp.h
    index f483945..cc1df2b 100644
    --- a/arch/x86/include/asm/smp.h
    +++ b/arch/x86/include/asm/smp.h
    @@ -31,12 +31,12 @@ static inline bool cpu_has_ht_siblings(void)
    return has_siblings;
    }

    -DECLARE_PER_CPU(cpumask_var_t, cpu_sibling_map);
    -DECLARE_PER_CPU(cpumask_var_t, cpu_core_map);
    +DECLARE_PER_CPU_READ_MOSTLY(cpumask_var_t, cpu_sibling_map);
    +DECLARE_PER_CPU_READ_MOSTLY(cpumask_var_t, cpu_core_map);
    /* cpus sharing the last level cache: */
    -DECLARE_PER_CPU(cpumask_var_t, cpu_llc_shared_map);
    -DECLARE_PER_CPU(u16, cpu_llc_id);
    -DECLARE_PER_CPU(int, cpu_number);
    +DECLARE_PER_CPU_READ_MOSTLY(cpumask_var_t, cpu_llc_shared_map);
    +DECLARE_PER_CPU_READ_MOSTLY(u16, cpu_llc_id);
    +DECLARE_PER_CPU_READ_MOSTLY(int, cpu_number);

    static inline struct cpumask *cpu_sibling_mask(int cpu)
    {
    @@ -53,10 +53,10 @@ static inline struct cpumask *cpu_llc_shared_mask(int cpu)
    return per_cpu(cpu_llc_shared_map, cpu);
    }

    -DECLARE_EARLY_PER_CPU(u16, x86_cpu_to_apicid);
    -DECLARE_EARLY_PER_CPU(u16, x86_bios_cpu_apicid);
    +DECLARE_EARLY_PER_CPU_READ_MOSTLY(u16, x86_cpu_to_apicid);
    +DECLARE_EARLY_PER_CPU_READ_MOSTLY(u16, x86_bios_cpu_apicid);
    #if defined(CONFIG_X86_LOCAL_APIC) && defined(CONFIG_X86_32)
    -DECLARE_EARLY_PER_CPU(int, x86_cpu_to_logical_apicid);
    +DECLARE_EARLY_PER_CPU_READ_MOSTLY(int, x86_cpu_to_logical_apicid);
    #endif

    /* Static state in head.S used to set up a CPU */
    diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
    index 39a222e..0443b64 100644
    --- a/arch/x86/kernel/apic/apic.c
    +++ b/arch/x86/kernel/apic/apic.c
    @@ -75,8 +75,8 @@ physid_mask_t phys_cpu_present_map;
    /*
    * Map cpu index to physical APIC ID
    */
    -DEFINE_EARLY_PER_CPU(u16, x86_cpu_to_apicid, BAD_APICID);
    -DEFINE_EARLY_PER_CPU(u16, x86_bios_cpu_apicid, BAD_APICID);
    +DEFINE_EARLY_PER_CPU_READ_MOSTLY(u16, x86_cpu_to_apicid, BAD_APICID);
    +DEFINE_EARLY_PER_CPU_READ_MOSTLY(u16, x86_bios_cpu_apicid, BAD_APICID);
    EXPORT_EARLY_PER_CPU_SYMBOL(x86_cpu_to_apicid);
    EXPORT_EARLY_PER_CPU_SYMBOL(x86_bios_cpu_apicid);

    @@ -88,7 +88,7 @@ EXPORT_EARLY_PER_CPU_SYMBOL(x86_bios_cpu_apicid);
    * used for the mapping. This is where the behaviors of x86_64 and 32
    * actually diverge. Let's keep it ugly for now.
    */
    -DEFINE_EARLY_PER_CPU(int, x86_cpu_to_logical_apicid, BAD_APICID);
    +DEFINE_EARLY_PER_CPU_READ_MOSTLY(int, x86_cpu_to_logical_apicid, BAD_APICID);

    /*
    * Knob to control our willingness to enable the local APIC.
    diff --git a/arch/x86/kernel/setup_percpu.c b/arch/x86/kernel/setup_percpu.c
    index 5a98aa2..5cdff03 100644
    --- a/arch/x86/kernel/setup_percpu.c
    +++ b/arch/x86/kernel/setup_percpu.c
    @@ -21,7 +21,7 @@
    #include <asm/cpu.h>
    #include <asm/stackprotector.h>

    -DEFINE_PER_CPU(int, cpu_number);
    +DEFINE_PER_CPU_READ_MOSTLY(int, cpu_number);
    EXPORT_PER_CPU_SYMBOL(cpu_number);

    #ifdef CONFIG_X86_64
    diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
    index 3fab55b..e61110e 100644
    --- a/arch/x86/kernel/smpboot.c
    +++ b/arch/x86/kernel/smpboot.c
    @@ -104,17 +104,17 @@ int smp_num_siblings = 1;
    EXPORT_SYMBOL(smp_num_siblings);

    /* Last level cache ID of each logical CPU */
    -DEFINE_PER_CPU(u16, cpu_llc_id) = BAD_APICID;
    +DEFINE_PER_CPU_READ_MOSTLY(u16, cpu_llc_id) = BAD_APICID;

    /* representing HT siblings of each logical CPU */
    -DEFINE_PER_CPU(cpumask_var_t, cpu_sibling_map);
    +DEFINE_PER_CPU_READ_MOSTLY(cpumask_var_t, cpu_sibling_map);
    EXPORT_PER_CPU_SYMBOL(cpu_sibling_map);

    /* representing HT and core siblings of each logical CPU */
    -DEFINE_PER_CPU(cpumask_var_t, cpu_core_map);
    +DEFINE_PER_CPU_READ_MOSTLY(cpumask_var_t, cpu_core_map);
    EXPORT_PER_CPU_SYMBOL(cpu_core_map);

    -DEFINE_PER_CPU(cpumask_var_t, cpu_llc_shared_map);
    +DEFINE_PER_CPU_READ_MOSTLY(cpumask_var_t, cpu_llc_shared_map);

    /* Per CPU bogomips and other parameters */
    DEFINE_PER_CPU_SHARED_ALIGNED(struct cpuinfo_x86, cpu_info);

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