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    SubjectRe: [PATCH] APICID: Avoid false sharing on the read mostly x86_cpu_to_apicid
    On 10/26/2011 08:21 AM, David Rientjes wrote:

    > On Tue, 25 Oct 2011, Eial Czerwacki wrote:
    >
    >> Avoid false sharing on the read mostly x86_cpu_to_apicid by moving it to
    >> __read_mostly section.
    >
    > x86_cpu_to_apicid used to be in .init.data and now it's never freed after
    > boot?
    >
    >> The per-cpu area is write and read and this symbol shows up high on ipi
    >> intensive/x86_cpu_to_apicid load.
    >>
    >> Signed-off-by: Eial Czerwacki<eial@scalemp.com>
    >> Signed-off-by: Shai Fultheim<shai@scalemp.com>
    >> Author: Ravikiran Thirumalai<kiran@scalex86.org>
    >
    > If the author isn't you, then the patch should start with a single line
    > that says "From: name <email>" of the author followed by a blank line.
    > It's also strange that the author doesn't have a sign-off line.
    >


    the author is mentioned after the last sign-off.

    > Your email client also has corrupted the inline patch, please see
    > Documentation/email-clients.txt.
    >


    thanks for the tips, I hope it is ok now.

    > And, finally, please send this to the x86 maintainers once fixed. See
    > ./scripts/get_maintainers.pl <your patch>.
    >


    sure.

    >> Index: b/arch/x86/include/asm/smp.h
    >> ===================================================================
    >> --- a/arch/x86/include/asm/smp.h 2010-06-01 09:56:03.000000000 -0700
    >> +++ b/arch/x86/include/asm/smp.h 2010-06-02 15:59:21.000000000 -0700
    >> @@ -36,7 +36,8 @@ static inline struct cpumask *cpu_core_m
    >> return per_cpu(cpu_core_map, cpu);
    >> }
    >>
    >> -DECLARE_EARLY_PER_CPU(u16, x86_cpu_to_apicid);
    >> +extern u16 x86_cpu_to_apicid[NR_CPUS];
    >> +
    >> DECLARE_EARLY_PER_CPU(u16, x86_bios_cpu_apicid);
    >>
    >> /* Static state in head.S used to set up a CPU */
    >> @@ -142,7 +143,7 @@ void native_send_call_func_ipi(const str
    >> void native_send_call_func_single_ipi(int cpu);
    >>
    >> void smp_store_cpu_info(int id);
    >> -#define cpu_physical_id(cpu) per_cpu(x86_cpu_to_apicid, cpu)
    >> +#define cpu_physical_id(cpu) x86_cpu_to_apicid[cpu]
    >>
    >> /* We don't mark CPUs online until __cpu_up(), so we need another measure */
    >> static inline int num_booting_cpus(void)
    >> Index: b/arch/x86/kernel/acpi/boot.c
    >> ===================================================================
    >> --- a/arch/x86/kernel/acpi/boot.c 2010-06-01 09:56:03.000000000 -0700
    >> +++ b/arch/x86/kernel/acpi/boot.c 2010-06-02 15:59:21.000000000 -0700
    >> @@ -568,7 +568,7 @@ EXPORT_SYMBOL(acpi_map_lsapic);
    >>
    >> int acpi_unmap_lsapic(int cpu)
    >> {
    >> - per_cpu(x86_cpu_to_apicid, cpu) = -1;
    >> + x86_cpu_to_apicid[cpu] = -1;
    >> set_cpu_present(cpu, false);
    >> num_processors--;
    >>
    >
    > Shouldn't this be BAD_APICID? Not sure where we check for -1.
    > --
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    >


    I'll check the rest of your comments.

    Thanks,

    Eial.


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