diff options
| -rw-r--r-- | include/linux/sched.h | 8 | ||||
| -rw-r--r-- | kernel/sched.c | 223 | ||||
| -rw-r--r-- | kernel/time/tick-sched.c | 9 |
3 files changed, 227 insertions, 13 deletions
diff --git a/include/linux/sched.h b/include/linux/sched.h index 6312521..15ab3e0 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -194,6 +194,14 @@ extern void sched_init_smp(void); extern void init_idle(struct task_struct *idle, int cpu); extern cpumask_t nohz_cpu_mask; +#if defined(CONFIG_SMP) && defined(CONFIG_NO_HZ) +extern int select_nohz_load_balancer(int cpu); +#else +static inline int select_nohz_load_balancer(int cpu) +{ + return 0; +} +#endif /* * Only dump TASK_* tasks. (0 for all tasks) diff --git a/kernel/sched.c b/kernel/sched.c index ba053d8..7459928 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -224,6 +224,9 @@ struct rq { #ifdef CONFIG_SMP unsigned long cpu_load[3]; unsigned char idle_at_tick; +#ifdef CONFIG_NO_HZ + unsigned char in_nohz_recently; +#endif #endif unsigned long long nr_switches; @@ -1050,6 +1053,17 @@ static void resched_task(struct task_struct *p) if (!tsk_is_polling(p)) smp_send_reschedule(cpu); } + +static void resched_cpu(int cpu) +{ + struct rq *rq = cpu_rq(cpu); + unsigned long flags; + + if (!spin_trylock_irqsave(&rq->lock, flags)) + return; + resched_task(cpu_curr(cpu)); + spin_unlock_irqrestore(&rq->lock, flags); +} #else static inline void resched_task(struct task_struct *p) { @@ -2658,6 +2672,12 @@ redo: double_rq_unlock(this_rq, busiest); local_irq_restore(flags); + /* + * some other cpu did the load balance for us. + */ + if (nr_moved && this_cpu != smp_processor_id()) + resched_cpu(this_cpu); + /* All tasks on this runqueue were pinned by CPU affinity */ if (unlikely(all_pinned)) { cpu_clear(cpu_of(busiest), cpus); @@ -2928,27 +2948,98 @@ static void update_load(struct rq *this_rq) } } +#ifdef CONFIG_NO_HZ +static struct { + atomic_t load_balancer; + cpumask_t cpu_mask; +} nohz ____cacheline_aligned = { + .load_balancer = ATOMIC_INIT(-1), + .cpu_mask = CPU_MASK_NONE, +}; + /* - * run_rebalance_domains is triggered when needed from the scheduler tick. + * This routine will try to nominate the ilb (idle load balancing) + * owner among the cpus whose ticks are stopped. ilb owner will do the idle + * load balancing on behalf of all those cpus. If all the cpus in the system + * go into this tickless mode, then there will be no ilb owner (as there is + * no need for one) and all the cpus will sleep till the next wakeup event + * arrives... + * + * For the ilb owner, tick is not stopped. And this tick will be used + * for idle load balancing. ilb owner will still be part of + * nohz.cpu_mask.. + * + * While stopping the tick, this cpu will become the ilb owner if there + * is no other owner. And will be the owner till that cpu becomes busy + * or if all cpus in the system stop their ticks at which point + * there is no need for ilb owner. * + * When the ilb owner becomes busy, it nominates another owner, during the + * next busy scheduler_tick() + */ +int select_nohz_load_balancer(int stop_tick) +{ + int cpu = smp_processor_id(); + + if (stop_tick) { + cpu_set(cpu, nohz.cpu_mask); + cpu_rq(cpu)->in_nohz_recently = 1; + + /* + * If we are going offline and still the leader, give up! + */ + if (cpu_is_offline(cpu) && + atomic_read(&nohz.load_balancer) == cpu) { + if (atomic_cmpxchg(&nohz.load_balancer, cpu, -1) != cpu) + BUG(); + return 0; + } + + /* time for ilb owner also to sleep */ + if (cpus_weight(nohz.cpu_mask) == num_online_cpus()) { + if (atomic_read(&nohz.load_balancer) == cpu) + atomic_set(&nohz.load_balancer, -1); + return 0; + } + + if (atomic_read(&nohz.load_balancer) == -1) { + /* make me the ilb owner */ + if (atomic_cmpxchg(&nohz.load_balancer, -1, cpu) == -1) + return 1; + } else if (atomic_read(&nohz.load_balancer) == cpu) + return 1; + } else { + if (!cpu_isset(cpu, nohz.cpu_mask)) + return 0; + + cpu_clear(cpu, nohz.cpu_mask); + + if (atomic_read(&nohz.load_balancer) == cpu) + if (atomic_cmpxchg(&nohz.load_balancer, cpu, -1) != cpu) + BUG(); + } + return 0; +} +#endif + +static DEFINE_SPINLOCK(balancing); + +/* * 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 DEFINE_SPINLOCK(balancing); - -static void run_rebalance_domains(struct softirq_action *h) +static inline void rebalance_domains(int cpu, enum idle_type idle) { - int this_cpu = smp_processor_id(), balance = 1; - struct rq *this_rq = cpu_rq(this_cpu); + int balance = 1; + struct rq *rq = cpu_rq(cpu); unsigned long interval; struct sched_domain *sd; - enum idle_type idle = this_rq->idle_at_tick ? SCHED_IDLE : NOT_IDLE; - /* Earliest time when we have to call run_rebalance_domains again */ + /* Earliest time when we have to do rebalance again */ unsigned long next_balance = jiffies + 60*HZ; - for_each_domain(this_cpu, sd) { + for_each_domain(cpu, sd) { if (!(sd->flags & SD_LOAD_BALANCE)) continue; @@ -2967,7 +3058,7 @@ static void run_rebalance_domains(struct softirq_action *h) } if (time_after_eq(jiffies, sd->last_balance + interval)) { - if (load_balance(this_cpu, this_rq, sd, idle, &balance)) { + if (load_balance(cpu, rq, sd, idle, &balance)) { /* * We've pulled tasks over so either we're no * longer idle, or one of our SMT siblings is @@ -2991,7 +3082,114 @@ out: if (!balance) break; } - this_rq->next_balance = next_balance; + rq->next_balance = next_balance; +} + +/* + * run_rebalance_domains is triggered when needed from the scheduler tick. + * In CONFIG_NO_HZ case, the idle load balance owner will do the + * rebalancing for all the cpus for whom scheduler ticks are stopped. + */ +static void run_rebalance_domains(struct softirq_action *h) +{ + int local_cpu = smp_processor_id(); + struct rq *local_rq = cpu_rq(local_cpu); + enum idle_type idle = local_rq->idle_at_tick ? SCHED_IDLE : NOT_IDLE; + + rebalance_domains(local_cpu, idle); + +#ifdef CONFIG_NO_HZ + /* + * If this cpu is the owner for idle load balancing, then do the + * balancing on behalf of the other idle cpus whose ticks are + * stopped. + */ + if (local_rq->idle_at_tick && + atomic_read(&nohz.load_balancer) == local_cpu) { + cpumask_t cpus = nohz.cpu_mask; + struct rq *rq; + int balance_cpu; + + cpu_clear(local_cpu, cpus); + for_each_cpu_mask(balance_cpu, cpus) { + /* + * If this cpu gets work to do, stop the load balancing + * work being done for other cpus. Next load + * balancing owner will pick it up. + */ + if (need_resched()) + break; + + rebalance_domains(balance_cpu, SCHED_IDLE); + + rq = cpu_rq(balance_cpu); + if (time_after(local_rq->next_balance, rq->next_balance)) + local_rq->next_balance = rq->next_balance; + } + } +#endif +} + +/* + * Trigger the SCHED_SOFTIRQ if it is time to do periodic load balancing. + * + * In case of CONFIG_NO_HZ, this is the place where we nominate a new + * idle load balancing owner or decide to stop the periodic load balancing, + * if the whole system is idle. + */ +static inline void trigger_load_balance(int cpu) +{ + struct rq *rq = cpu_rq(cpu); +#ifdef CONFIG_NO_HZ + /* + * If we were in the nohz mode recently and busy at the current + * scheduler tick, then check if we need to nominate new idle + * load balancer. + */ + if (rq->in_nohz_recently && !rq->idle_at_tick) { + rq->in_nohz_recently = 0; + + if (atomic_read(&nohz.load_balancer) == cpu) { + cpu_clear(cpu, nohz.cpu_mask); + atomic_set(&nohz.load_balancer, -1); + } + + if (atomic_read(&nohz.load_balancer) == -1) { + /* + * simple selection for now: Nominate the + * first cpu in the nohz list to be the next + * ilb owner. + * + * TBD: Traverse the sched domains and nominate + * the nearest cpu in the nohz.cpu_mask. + */ + int ilb = first_cpu(nohz.cpu_mask); + + if (ilb != NR_CPUS) + resched_cpu(ilb); + } + } + + /* + * If this cpu is idle and doing idle load balancing for all the + * cpus with ticks stopped, is it time for that to stop? + */ + if (rq->idle_at_tick && atomic_read(&nohz.load_balancer) == cpu && + cpus_weight(nohz.cpu_mask) == num_online_cpus()) { + resched_cpu(cpu); + return; + } + + /* + * If this cpu is idle and the idle load balancing is done by + * someone else, then no need raise the SCHED_SOFTIRQ + */ + if (rq->idle_at_tick && atomic_read(&nohz.load_balancer) != cpu && + cpu_isset(cpu, nohz.cpu_mask)) + return; +#endif + if (time_after_eq(jiffies, rq->next_balance)) + raise_softirq(SCHED_SOFTIRQ); } #else /* @@ -3224,8 +3422,7 @@ void scheduler_tick(void) #ifdef CONFIG_SMP update_load(rq); rq->idle_at_tick = idle_at_tick; - if (time_after_eq(jiffies, rq->next_balance)) - raise_softirq(SCHED_SOFTIRQ); + trigger_load_balance(cpu); #endif } diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index f4fc867..3483e6c 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -217,6 +217,14 @@ void tick_nohz_stop_sched_tick(void) * the scheduler tick in nohz_restart_sched_tick. */ if (!ts->tick_stopped) { + if (select_nohz_load_balancer(1)) { + /* + * sched tick not stopped! + */ + cpu_clear(cpu, nohz_cpu_mask); + goto out; + } + ts->idle_tick = ts->sched_timer.expires; ts->tick_stopped = 1; ts->idle_jiffies = last_jiffies; @@ -285,6 +293,7 @@ void tick_nohz_restart_sched_tick(void) now = ktime_get(); local_irq_disable(); + select_nohz_load_balancer(0); tick_do_update_jiffies64(now); cpu_clear(cpu, nohz_cpu_mask); |