sched: Remove double_rq_lock() from __migrate_task()
Avoid double_rq_lock() and use TASK_ON_RQ_MIGRATING for __migrate_task(). The advantage is (obviously) not holding two rq->lock's at the same time and thereby increasing parallelism. The important point to note is that because we acquire dst->lock immediately after releasing src->lock the potential wait time of task_rq_lock() callers on TASK_ON_RQ_MIGRATING is not longer than it would have been in the double rq lock scenario. Signed-off-by: Kirill Tkhai <ktkhai@parallels.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Paul Turner <pjt@google.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Mike Galbraith <umgwanakikbuti@gmail.com> Cc: Kirill Tkhai <tkhai@yandex.ru> Cc: Tim Chen <tim.c.chen@linux.intel.com> Cc: Nicolas Pitre <nicolas.pitre@linaro.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Link: http://lkml.kernel.org/r/1408528070.23412.89.camel@tkhai Signed-off-by: Ingo Molnar <mingo@kernel.org>
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@ -4679,20 +4679,20 @@ EXPORT_SYMBOL_GPL(set_cpus_allowed_ptr);
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*/
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static int __migrate_task(struct task_struct *p, int src_cpu, int dest_cpu)
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{
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struct rq *rq_dest, *rq_src;
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struct rq *rq;
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int ret = 0;
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if (unlikely(!cpu_active(dest_cpu)))
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return ret;
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rq_src = cpu_rq(src_cpu);
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rq_dest = cpu_rq(dest_cpu);
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rq = cpu_rq(src_cpu);
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raw_spin_lock(&p->pi_lock);
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double_rq_lock(rq_src, rq_dest);
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raw_spin_lock(&rq->lock);
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/* Already moved. */
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if (task_cpu(p) != src_cpu)
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goto done;
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/* Affinity changed (again). */
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if (!cpumask_test_cpu(dest_cpu, tsk_cpus_allowed(p)))
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goto fail;
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@ -4702,15 +4702,22 @@ static int __migrate_task(struct task_struct *p, int src_cpu, int dest_cpu)
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* placed properly.
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*/
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if (task_on_rq_queued(p)) {
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dequeue_task(rq_src, p, 0);
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dequeue_task(rq, p, 0);
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p->on_rq = TASK_ON_RQ_MIGRATING;
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set_task_cpu(p, dest_cpu);
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enqueue_task(rq_dest, p, 0);
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check_preempt_curr(rq_dest, p, 0);
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raw_spin_unlock(&rq->lock);
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rq = cpu_rq(dest_cpu);
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raw_spin_lock(&rq->lock);
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BUG_ON(task_rq(p) != rq);
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p->on_rq = TASK_ON_RQ_QUEUED;
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enqueue_task(rq, p, 0);
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check_preempt_curr(rq, p, 0);
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}
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done:
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ret = 1;
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fail:
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double_rq_unlock(rq_src, rq_dest);
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raw_spin_unlock(&rq->lock);
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raw_spin_unlock(&p->pi_lock);
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return ret;
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}
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