sched: Do not stop cpu in set_cpus_allowed_ptr() if task is not running

If a task is queued but not running on it rq, we can simply migrate
it without migration thread and switching of context.

Signed-off-by: Kirill Tkhai <ktkhai@parallels.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1410519814.3569.7.camel@tkhai
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 32 insertions, 15 deletions

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 5536397a0309..4b1ddebed54a 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4629,6 +4629,33 @@ void init_idle(struct task_struct *idle, int cpu)
 }
 
 #ifdef CONFIG_SMP
+/*
+ * move_queued_task - move a queued task to new rq.
+ *
+ * Returns (locked) new rq. Old rq's lock is released.
+ */
+static struct rq *move_queued_task(struct task_struct *p, int new_cpu)
+{
+        struct rq *rq = task_rq(p);
+
+        lockdep_assert_held(&rq->lock);
+
+        dequeue_task(rq, p, 0);
+        p->on_rq = TASK_ON_RQ_MIGRATING;
+        set_task_cpu(p, new_cpu);
+        raw_spin_unlock(&rq->lock);
+
+        rq = cpu_rq(new_cpu);
+
+        raw_spin_lock(&rq->lock);
+        BUG_ON(task_cpu(p) != new_cpu);
+        p->on_rq = TASK_ON_RQ_QUEUED;
+        enqueue_task(rq, p, 0);
+        check_preempt_curr(rq, p, 0);
+
+        return rq;
+}
+
 void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask)
 {
         if (p->sched_class && p->sched_class->set_cpus_allowed)
@@ -4685,14 +4712,15 @@ int set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask)
                 goto out;
 
         dest_cpu = cpumask_any_and(cpu_active_mask, new_mask);
-        if (task_on_rq_queued(p) || p->state == TASK_WAKING) {
+        if (task_running(rq, p) || p->state == TASK_WAKING) {
                 struct migration_arg arg = { p, dest_cpu };
                 /* Need help from migration thread: drop lock and wait. */
                 task_rq_unlock(rq, p, &flags);
                 stop_one_cpu(cpu_of(rq), migration_cpu_stop, &arg);
                 tlb_migrate_finish(p->mm);
                 return 0;
-        }
+        } else if (task_on_rq_queued(p))
+                rq = move_queued_task(p, dest_cpu);
 out:
         task_rq_unlock(rq, p, &flags);
 
@@ -4735,19 +4763,8 @@ static int __migrate_task(struct task_struct *p, int src_cpu, int dest_cpu)
          * If we're not on a rq, the next wake-up will ensure we're
          * placed properly.
          */
-        if (task_on_rq_queued(p)) {
-                dequeue_task(rq, p, 0);
-                p->on_rq = TASK_ON_RQ_MIGRATING;
-                set_task_cpu(p, dest_cpu);
-                raw_spin_unlock(&rq->lock);
-
-                rq = cpu_rq(dest_cpu);
-                raw_spin_lock(&rq->lock);
-                BUG_ON(task_rq(p) != rq);
-                p->on_rq = TASK_ON_RQ_QUEUED;
-                enqueue_task(rq, p, 0);
-                check_preempt_curr(rq, p, 0);
-        }
+        if (task_on_rq_queued(p))
+                rq = move_queued_task(p, dest_cpu);
 done:
         ret = 1;
 fail: