Index: linux-2.6/kernel/sched.c =================================================================== --- linux-2.6.orig/kernel/sched.c 2006-06-02 18:51:25.000000000 +1000 +++ linux-2.6/kernel/sched.c 2006-06-02 18:54:38.000000000 +1000 @@ -239,7 +239,6 @@ struct runqueue { task_t *migration_thread; struct list_head migration_queue; - int cpu; #endif #ifdef CONFIG_SCHEDSTATS @@ -1687,7 +1686,7 @@ unsigned long nr_active(void) * double_rq_lock - safely lock two runqueues * * We must take them in cpu order to match code in - * dependent_sleeper and wake_dependent_sleeper. + * wake_dependent_sleeper. * * Note this does not disable interrupts like task_rq_lock, * you need to do so manually before calling. @@ -1700,7 +1699,7 @@ static void double_rq_lock(runqueue_t *r spin_lock(&rq1->lock); __acquire(rq2->lock); /* Fake it out ;) */ } else { - if (rq1->cpu < rq2->cpu) { + if (rq1 < rq2) { spin_lock(&rq1->lock); spin_lock(&rq2->lock); } else { @@ -1736,7 +1735,7 @@ static void double_lock_balance(runqueue __acquires(this_rq->lock) { if (unlikely(!spin_trylock(&busiest->lock))) { - if (busiest->cpu < this_rq->cpu) { + if (busiest < this_rq) { spin_unlock(&this_rq->lock); spin_lock(&busiest->lock); spin_lock(&this_rq->lock); @@ -2686,6 +2685,9 @@ static inline void wakeup_busy_runqueue( resched_task(rq->idle); } +/* + * Called with interrupts disabled and this_rq's runqueue locked. + */ static void wake_sleeping_dependent(int this_cpu, runqueue_t *this_rq) { struct sched_domain *tmp, *sd = NULL; @@ -2693,41 +2695,24 @@ static void wake_sleeping_dependent(int int i; for_each_domain(this_cpu, tmp) - if (tmp->flags & SD_SHARE_CPUPOWER) + if (tmp->flags & SD_SHARE_CPUPOWER) { sd = tmp; - + break; + } if (!sd) return; - /* - * Unlock the current runqueue because we have to lock in - * CPU order to avoid deadlocks. Caller knows that we might - * unlock. We keep IRQs disabled. - */ - spin_unlock(&this_rq->lock); - sibling_map = sd->span; - - for_each_cpu_mask(i, sibling_map) - spin_lock(&cpu_rq(i)->lock); - /* - * We clear this CPU from the mask. This both simplifies the - * inner loop and keps this_rq locked when we exit: - */ cpu_clear(this_cpu, sibling_map); - for_each_cpu_mask(i, sibling_map) { runqueue_t *smt_rq = cpu_rq(i); + if (unlikely(!spin_trylock(&smt_rq->lock))) + continue; wakeup_busy_runqueue(smt_rq); - } - for_each_cpu_mask(i, sibling_map) - spin_unlock(&cpu_rq(i)->lock); - /* - * We exit with this_cpu's rq still held and IRQs - * still disabled: - */ + spin_unlock(&smt_rq->lock); + } } /* @@ -2740,48 +2725,38 @@ static inline unsigned long smt_slice(ta return p->time_slice * (100 - sd->per_cpu_gain) / 100; } -static int dependent_sleeper(int this_cpu, runqueue_t *this_rq) +/* + * To minimise lock contention and not have to drop this_rq's runlock we only + * trylock the sibling runqueues and bypass those runqueues if we fail to + * acquire their lock. As we only trylock the normal locking order does not + * need to be obeyed. + */ +static int dependent_sleeper(int this_cpu, struct runqueue *this_rq, + struct task_struct *p) { struct sched_domain *tmp, *sd = NULL; cpumask_t sibling_map; - prio_array_t *array; int ret = 0, i; - task_t *p; for_each_domain(this_cpu, tmp) - if (tmp->flags & SD_SHARE_CPUPOWER) + if (tmp->flags & SD_SHARE_CPUPOWER) { sd = tmp; - + break; + } if (!sd) return 0; - /* - * The same locking rules and details apply as for - * wake_sleeping_dependent(): - */ - spin_unlock(&this_rq->lock); sibling_map = sd->span; - for_each_cpu_mask(i, sibling_map) - spin_lock(&cpu_rq(i)->lock); cpu_clear(this_cpu, sibling_map); + for_each_cpu_mask(i, sibling_map) { + runqueue_t *smt_rq; + task_t *smt_curr; - /* - * Establish next task to be run - it might have gone away because - * we released the runqueue lock above: - */ - if (!this_rq->nr_running) - goto out_unlock; - array = this_rq->active; - if (!array->nr_active) - array = this_rq->expired; - BUG_ON(!array->nr_active); - - p = list_entry(array->queue[sched_find_first_bit(array->bitmap)].next, - task_t, run_list); + smt_rq = cpu_rq(i); + if (unlikely(!spin_trylock(&smt_rq->lock))) + continue; - for_each_cpu_mask(i, sibling_map) { - runqueue_t *smt_rq = cpu_rq(i); - task_t *smt_curr = smt_rq->curr; + smt_curr = smt_rq->curr; /* Kernel threads do not participate in dependent sleeping */ if (!p->mm || !smt_curr->mm || rt_task(p)) @@ -2834,10 +2809,10 @@ check_smt_task: else wakeup_busy_runqueue(smt_rq); } + + spin_unlock(&smt_rq->lock); } -out_unlock: - for_each_cpu_mask(i, sibling_map) - spin_unlock(&cpu_rq(i)->lock); + return ret; } #else @@ -2845,7 +2820,8 @@ static inline void wake_sleeping_depende { } -static inline int dependent_sleeper(int this_cpu, runqueue_t *this_rq) +static inline int dependent_sleeper(int this_cpu, struct runqueue *this_rq, + struct task_struct *p) { return 0; } @@ -2967,32 +2943,13 @@ need_resched_nonpreemptible: cpu = smp_processor_id(); if (unlikely(!rq->nr_running)) { -go_idle: idle_balance(cpu, rq); if (!rq->nr_running) { next = rq->idle; rq->expired_timestamp = 0; wake_sleeping_dependent(cpu, rq); - /* - * wake_sleeping_dependent() might have released - * the runqueue, so break out if we got new - * tasks meanwhile: - */ - if (!rq->nr_running) - goto switch_tasks; - } - } else { - if (dependent_sleeper(cpu, rq)) { - next = rq->idle; goto switch_tasks; } - /* - * dependent_sleeper() releases and reacquires the runqueue - * lock, hence go into the idle loop if the rq went - * empty meanwhile: - */ - if (unlikely(!rq->nr_running)) - goto go_idle; } array = rq->active; @@ -3030,6 +2987,8 @@ go_idle: } } next->sleep_type = SLEEP_NORMAL; + if (dependent_sleeper(cpu, rq, next)) + next = rq->idle; switch_tasks: if (next == rq->idle) schedstat_inc(rq, sched_goidle); @@ -6126,7 +6085,6 @@ void __init sched_init(void) rq->push_cpu = 0; rq->migration_thread = NULL; INIT_LIST_HEAD(&rq->migration_queue); - rq->cpu = i; #endif atomic_set(&rq->nr_iowait, 0);