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    Subject[PATCH 4/5] Create rebalance_domains from rebalance_tick
    Create rebalance_domains() from rebalance_tick().

    Essentially rebalance_domains = rebalance_tick. However, we
    do the idle calculation on our own. This removes some processing
    from scheduler_tick into rebalance_domains().

    While we are at it: Take the opportunity to avoid taking
    the request queue lock in wake_priority_sleeper if
    there are no running processes.

    Signed-off-by: Christoph Lameter <clameter@sgi.com>

    Index: linux-2.6.19-rc2-mm2/kernel/sched.c
    ===================================================================
    --- linux-2.6.19-rc2-mm2.orig/kernel/sched.c 2006-10-24 10:39:13.782726627 -0500
    +++ linux-2.6.19-rc2-mm2/kernel/sched.c 2006-10-24 10:40:32.928543506 -0500
    @@ -2842,18 +2842,22 @@ static void update_load(struct rq *this_
    }

    /*
    - * rebalance_tick will get called every timer tick, on every CPU.
    + * rebalance_domains is called from the scheduler_tick.
    *
    * It checks each scheduling domain to see if it is due to be balanced,
    * and initiates a balancing operation if so.
    *
    * Balancing parameters are set up in arch_init_sched_domains.
    */
    -static void
    -rebalance_tick(int this_cpu, struct rq *this_rq, enum idle_type idle)
    +static void rebalance_domains(unsigned long dummy)
    {
    + int this_cpu = smp_processor_id();
    + struct rq *this_rq = cpu_rq(this_cpu);
    unsigned long interval;
    struct sched_domain *sd;
    + /* Idle means on the idle queue without a runnable task */
    + enum idle_type idle = (this_rq->idle && !this_rq->nr_running) ?
    + SCHED_IDLE : NOT_IDLE;

    for_each_domain(this_cpu, sd) {
    if (!(sd->flags & SD_LOAD_BALANCE))
    @@ -2885,34 +2889,26 @@ rebalance_tick(int this_cpu, struct rq *
    /*
    * on UP we do not need to balance between CPUs:
    */
    -static inline void rebalance_tick(int cpu, struct rq *rq, enum idle_type idle)
    -{
    -}
    static inline void idle_balance(int cpu, struct rq *rq)
    {
    }
    -static inline void update_load(struct rq *this_rq)
    -{
    -}
    #endif

    -static inline int wake_priority_sleeper(struct rq *rq)
    +static inline void wake_priority_sleeper(struct rq *rq)
    {
    - int ret = 0;
    -
    #ifdef CONFIG_SCHED_SMT
    + if (!rq->nr_running)
    + return;
    +
    spin_lock(&rq->lock);
    /*
    * If an SMT sibling task has been put to sleep for priority
    * reasons reschedule the idle task to see if it can now run.
    */
    - if (rq->nr_running) {
    + if (rq->nr_running)
    resched_task(rq->idle);
    - ret = 1;
    - }
    spin_unlock(&rq->lock);
    #endif
    - return ret;
    }

    DEFINE_PER_CPU(struct kernel_stat, kstat);
    @@ -3123,17 +3119,15 @@ void scheduler_tick(void)
    struct task_struct *p = current;
    int cpu = smp_processor_id();
    struct rq *rq = cpu_rq(cpu);
    - enum idle_type idle = NOT_IDLE;

    update_cpu_clock(p, rq, now);

    rq->timestamp_last_tick = now;

    - if (p == rq->idle) {
    + if (p == rq->idle)
    /* Task on the idle queue */
    - if (!wake_priority_sleeper(rq))
    - idle = SCHED_IDLE;
    - } else {
    + wake_priority_sleeper(rq);
    + else {
    /* Task on cpu queue */
    if (p->array != rq->active)
    /* Task has expired but was not scheduled yet */
    @@ -3141,8 +3135,10 @@ void scheduler_tick(void)
    else
    time_slice(rq, p);
    }
    +#ifdef CONFIG_SMP
    update_load(rq);
    - rebalance_tick(cpu, rq, idle);
    + rebalance_domains(0L);
    +#endif
    }

    #ifdef CONFIG_SCHED_SMT
    -
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