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    Subject[PATCH 09/12] sched: add notifier for cross-cpu migrations
    Date
    Add a notifier to publish when a task gets migrated from one cpu to
    another. The first intended use is to export a "migration counter"
    to usermode so that a task can tell whether its still running on the
    same cpu (for use in vgetcpu and other vsyscall code).

    Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
    Cc: Avi Kivity <avi@redhat.com>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Ingo Molnar <mingo@elte.hu>
    Cc: Andi Kleen <ak@linux.intel.com>
    ---
    include/linux/sched.h | 8 ++++++++
    kernel/sched.c | 14 ++++++++++++++
    2 files changed, 22 insertions(+), 0 deletions(-)

    diff --git a/include/linux/sched.h b/include/linux/sched.h
    index 0f1ea4a..5186dd9 100644
    --- a/include/linux/sched.h
    +++ b/include/linux/sched.h
    @@ -141,6 +141,14 @@ extern unsigned long nr_iowait(void);
    extern void calc_global_load(void);
    extern u64 cpu_nr_migrations(int cpu);

    +/* Notifier for when a task gets migrated to a new CPU */
    +struct task_migration_notifier {
    + struct task_struct *task;
    + int from_cpu;
    + int to_cpu;
    +};
    +extern void register_task_migration_notifier(struct notifier_block *n);
    +
    extern unsigned long get_parent_ip(unsigned long addr);

    struct seq_file;
    diff --git a/kernel/sched.c b/kernel/sched.c
    index 1b59e26..3982e8e 100644
    --- a/kernel/sched.c
    +++ b/kernel/sched.c
    @@ -1951,6 +1951,12 @@ task_hot(struct task_struct *p, u64 now, struct sched_domain *sd)
    return delta < (s64)sysctl_sched_migration_cost;
    }

    +static ATOMIC_NOTIFIER_HEAD(task_migration_notifier);
    +
    +void register_task_migration_notifier(struct notifier_block *n)
    +{
    + atomic_notifier_chain_register(&task_migration_notifier, n);
    +}

    void set_task_cpu(struct task_struct *p, unsigned int new_cpu)
    {
    @@ -1973,6 +1979,8 @@ void set_task_cpu(struct task_struct *p, unsigned int new_cpu)
    p->se.block_start -= clock_offset;
    #endif
    if (old_cpu != new_cpu) {
    + struct task_migration_notifier tmn;
    +
    p->se.nr_migrations++;
    new_rq->nr_migrations_in++;
    #ifdef CONFIG_SCHEDSTATS
    @@ -1981,6 +1989,12 @@ void set_task_cpu(struct task_struct *p, unsigned int new_cpu)
    #endif
    perf_swcounter_event(PERF_COUNT_SW_CPU_MIGRATIONS,
    1, 1, NULL, 0);
    +
    + tmn.task = p;
    + tmn.from_cpu = old_cpu;
    + tmn.to_cpu = new_cpu;
    +
    + atomic_notifier_call_chain(&task_migration_notifier, 0, &tmn);
    }
    p->se.vruntime -= old_cfsrq->min_vruntime -
    new_cfsrq->min_vruntime;
    --
    1.6.2.5


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