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    Subject[PATCH 4/7] SMP: Implement on_one_cpu()
    Date
    This defines on_one_cpu() which is similar to smp_call_function_single()
    except that it works if cpu happens to be the current cpu. Can also be
    seen as a complement to on_each_cpu() (which also doesn't treat the
    current cpu specially).

    Signed-off-by: Avi Kivity <avi@qumranet.com>
    ---
    include/linux/smp.h | 15 +++++++++++++++
    kernel/softirq.c | 24 ++++++++++++++++++++++++
    2 files changed, 39 insertions(+), 0 deletions(-)

    diff --git a/include/linux/smp.h b/include/linux/smp.h
    index 3f70149..4ff8d68 100644
    --- a/include/linux/smp.h
    +++ b/include/linux/smp.h
    @@ -60,6 +60,11 @@ int smp_call_function_single(int cpuid, void (*func) (void *info), void *info,
    * Call a function on all processors
    */
    int on_each_cpu(void (*func) (void *info), void *info, int retry, int wait);
    +/*
    + * Call a function on one processor
    + */
    +int on_one_cpu(int cpu, void (*func)(void *info), void *info,
    + int retry, int wait);

    #define MSG_ALL_BUT_SELF 0x8000 /* Assume <32768 CPU's */
    #define MSG_ALL 0x8001
    @@ -95,6 +100,16 @@ static inline int up_smp_call_function(void)
    local_irq_enable(); \
    0; \
    })
    +
    +static inline int on_one_cpu(int cpu, void (*func)(void *info), void *info,
    + int retry, int wait)
    +{
    + local_irq_disable();
    + func(info);
    + local_irq_enable();
    + return 0;
    +}
    +
    static inline void smp_send_reschedule(int cpu) { }
    #define num_booting_cpus() 1
    #define smp_prepare_boot_cpu() do {} while (0)
    diff --git a/kernel/softirq.c b/kernel/softirq.c
    index 0b9886a..b1a3284 100644
    --- a/kernel/softirq.c
    +++ b/kernel/softirq.c
    @@ -658,4 +658,28 @@ int on_each_cpu(void (*func) (void *info), void *info, int retry, int wait)
    return ret;
    }
    EXPORT_SYMBOL(on_each_cpu);
    +
    +/*
    + * Call a function on one processor, which might be the currently executing
    + * processor.
    + */
    +int on_one_cpu(int cpu, void (*func) (void *info), void *info,
    + int retry, int wait)
    +{
    + int ret;
    + int this_cpu;
    +
    + this_cpu = get_cpu();
    + if (this_cpu == cpu) {
    + local_irq_disable();
    + func(info);
    + local_irq_enable();
    + ret = 0;
    + } else
    + ret = smp_call_function_single(cpu, func, info, retry, wait);
    + put_cpu();
    + return ret;
    +}
    +EXPORT_SYMBOL(on_one_cpu);
    +
    #endif
    --
    1.5.0.6
    -
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