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    Subject[patch 4/8] RT overloaded runqueues accounting
    This patch adds an RT overload accounting system. When a runqueue has
    more than one RT task queued, it is marked as overloaded. That is that it
    is a candidate to have RT tasks pulled from it.

    Along with the rt_overload counter (number of overloaded runqueues) a
    bit mask of overloaded runqueues with RT tasks is set.

    Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
    ---
    kernel/sched_rt.c | 19 +++++++++++++++++++
    1 file changed, 19 insertions(+)

    Index: linux-test.git/kernel/sched_rt.c
    ===================================================================
    --- linux-test.git.orig/kernel/sched_rt.c 2007-10-19 12:34:46.000000000 -0400
    +++ linux-test.git/kernel/sched_rt.c 2007-10-19 12:35:58.000000000 -0400
    @@ -25,10 +25,23 @@ static void update_curr_rt(struct rq *rq
    curr->se.exec_start = rq->clock;
    }

    +#ifdef CONFIG_SMP
    +static __cacheline_aligned_in_smp atomic_t rt_overload;
    +static cpumask_t rto_cpumask;
    +#endif /* CONFIG_SMP*/
    +
    static inline void inc_rt_tasks(struct task_struct *p, struct rq *rq)
    {
    if (rt_task(p))
    rq->rt_nr_running++;
    +#ifdef CONFIG_SMP
    + if (rq->rt_nr_running == 2) {
    + cpu_set(rq->cpu, rto_cpumask);
    + /* Make sure this cpu is visible on rt_overloads */
    + smp_wmb();
    + atomic_inc(&rt_overload);
    + }
    +#endif
    }

    static inline void dec_rt_tasks(struct task_struct *p, struct rq *rq)
    @@ -37,6 +50,12 @@ static inline void dec_rt_tasks(struct t
    WARN_ON(!rq->rt_nr_running);
    rq->rt_nr_running--;
    }
    +#ifdef CONFIG_SMP
    + if (rq->rt_nr_running == 1) {
    + atomic_dec(&rt_overload);
    + cpu_clear(rq->cpu, rto_cpumask);
    + }
    +#endif
    }

    static void enqueue_task_rt(struct rq *rq, struct task_struct *p, int wakeup)
    --
    -
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