From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754486AbbFKMyj (ORCPT ); Thu, 11 Jun 2015 08:54:39 -0400 Received: from bombadil.infradead.org ([198.137.202.9]:56781 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753211AbbFKMyC (ORCPT ); Thu, 11 Jun 2015 08:54:02 -0400 Message-Id: <20150611124743.755256708@infradead.org> User-Agent: quilt/0.61-1 Date: Thu, 11 Jun 2015 14:46:51 +0200 From: Peter Zijlstra To: umgwanakikbuti@gmail.com, mingo@elte.hu Cc: ktkhai@parallels.com, rostedt@goodmis.org, tglx@linutronix.de, juri.lelli@gmail.com, pang.xunlei@linaro.org, oleg@redhat.com, wanpeng.li@linux.intel.com, linux-kernel@vger.kernel.org, peterz@infradead.org Subject: [PATCH 15/18] sched: Streamline the task migration locking a little References: <20150611124636.448700267@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline; filename=peterz-sched-migrate-locking.patch Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The whole migrate_task{,s}() locking seems a little shaky, there's a lot of dropping an require happening. Pull the locking up into the callers as far as possible to streamline the lot. Signed-off-by: Peter Zijlstra (Intel) --- kernel/sched/core.c | 76 +++++++++++++++++++++++----------------------------- 1 file changed, 34 insertions(+), 42 deletions(-) --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -1065,10 +1065,8 @@ void check_preempt_curr(struct rq *rq, s * * Returns (locked) new rq. Old rq's lock is released. */ -static struct rq *move_queued_task(struct task_struct *p, int new_cpu) +static struct rq *move_queued_task(struct rq *rq, struct task_struct *p, int new_cpu) { - struct rq *rq = task_rq(p); - lockdep_assert_held(&rq->lock); dequeue_task(rq, p, 0); @@ -1100,41 +1098,19 @@ struct migration_arg { * * So we race with normal scheduler movements, but that's OK, as long * as the task is no longer on this CPU. - * - * Returns non-zero if task was successfully migrated. */ -static int __migrate_task(struct task_struct *p, int src_cpu, int dest_cpu) +static struct rq *__migrate_task(struct rq *rq, struct task_struct *p, int dest_cpu) { - struct rq *rq; - int ret = 0; - if (unlikely(!cpu_active(dest_cpu))) - return ret; - - rq = cpu_rq(src_cpu); - - raw_spin_lock(&p->pi_lock); - raw_spin_lock(&rq->lock); - /* Already moved. */ - if (task_cpu(p) != src_cpu) - goto done; + return rq; /* Affinity changed (again). */ if (!cpumask_test_cpu(dest_cpu, tsk_cpus_allowed(p))) - goto fail; + return rq; - /* - * If we're not on a rq, the next wake-up will ensure we're - * placed properly. - */ - if (task_on_rq_queued(p)) - rq = move_queued_task(p, dest_cpu); -done: - ret = 1; -fail: - raw_spin_unlock(&rq->lock); - raw_spin_unlock(&p->pi_lock); - return ret; + rq = move_queued_task(rq, p, dest_cpu); + + return rq; } /* @@ -1145,6 +1121,8 @@ static int __migrate_task(struct task_st static int migration_cpu_stop(void *data) { struct migration_arg *arg = data; + struct task_struct *p = arg->task; + struct rq *rq = this_rq(); /* * The original target cpu might have gone down and we might @@ -1157,7 +1135,19 @@ static int migration_cpu_stop(void *data * during wakeups, see set_cpus_allowed_ptr()'s TASK_WAKING test. */ sched_ttwu_pending(); - __migrate_task(arg->task, raw_smp_processor_id(), arg->dest_cpu); + + raw_spin_lock(&p->pi_lock); + raw_spin_lock(&rq->lock); + /* + * If task_rq(p) != rq, it cannot be migrated here, because we're + * holding rq->lock, if p->on_rq == 0 it cannot get enqueued because + * we're holding p->pi_lock. + */ + if (task_rq(p) == rq && task_on_rq_queued(p)) + rq = __migrate_task(rq, p, arg->dest_cpu); + raw_spin_unlock(&rq->lock); + raw_spin_unlock(&p->pi_lock); + local_irq_enable(); return 0; } @@ -1212,7 +1202,7 @@ int set_cpus_allowed_ptr(struct task_str tlb_migrate_finish(p->mm); return 0; } else if (task_on_rq_queued(p)) - rq = move_queued_task(p, dest_cpu); + rq = move_queued_task(rq, p, dest_cpu); out: task_rq_unlock(rq, p, &flags); @@ -5049,9 +5039,9 @@ static struct task_struct fake_task = { * there's no concurrency possible, we hold the required locks anyway * because of lock validation efforts. */ -static void migrate_tasks(unsigned int dead_cpu) +static void migrate_tasks(struct rq *dead_rq) { - struct rq *rq = cpu_rq(dead_cpu); + struct rq *rq = dead_rq; struct task_struct *next, *stop = rq->stop; int dest_cpu; @@ -5073,7 +5063,7 @@ static void migrate_tasks(unsigned int d */ update_rq_clock(rq); - for ( ; ; ) { + for (;;) { /* * There's this thread running, bail when that's the only * remaining thread. @@ -5086,12 +5076,14 @@ static void migrate_tasks(unsigned int d next->sched_class->put_prev_task(rq, next); /* Find suitable destination for @next, with force if needed. */ - dest_cpu = select_fallback_rq(dead_cpu, next); - raw_spin_unlock(&rq->lock); - - __migrate_task(next, dead_cpu, dest_cpu); + dest_cpu = select_fallback_rq(dead_rq->cpu, next); - raw_spin_lock(&rq->lock); + rq = __migrate_task(rq, next, dest_cpu); + if (rq != dead_rq) { + raw_spin_unlock(&rq->lock); + rq = dead_rq; + raw_spin_lock(&rq->lock); + } } rq->stop = stop; @@ -5343,7 +5335,7 @@ migration_call(struct notifier_block *nf BUG_ON(!cpumask_test_cpu(cpu, rq->rd->span)); set_rq_offline(rq); } - migrate_tasks(cpu); + migrate_tasks(rq); BUG_ON(rq->nr_running != 1); /* the migration thread */ raw_spin_unlock_irqrestore(&rq->lock, flags); break;