[PATCH 19/21] sched: Restructure ttwu some more

[Peter Zijlstra]

The last few changes to ttwu that allow for adding remote queues.

Reviewed-by: Frank Rowand <frank.rowand@xxxxxxxxxxx>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
---
 kernel/sched.c |   93 ++++++++++++++++++++++++++++++++++++---------------------
 1 file changed, 59 insertions(+), 34 deletions(-)

Index: linux-2.6/kernel/sched.c
===================================================================
--- linux-2.6.orig/kernel/sched.c
+++ linux-2.6/kernel/sched.c
@@ -2474,6 +2474,49 @@ ttwu_do_wakeup(struct rq *rq, struct tas
 		wq_worker_waking_up(p, cpu_of(rq));
 }
 
+static void
+ttwu_do_activate(struct rq *rq, struct task_struct *p, int wake_flags)
+{
+#ifdef CONFIG_SMP
+	if (p->sched_contributes_to_load)
+		rq->nr_uninterruptible--;
+#endif
+
+	activate_task(rq, p, ENQUEUE_WAKEUP | ENQUEUE_WAKING);
+	p->on_rq = 1;
+	ttwu_do_wakeup(rq, p, wake_flags);
+}
+
+/*
+ * Called in case the task @p isn't fully descheduled from its runqueue,
+ * in this case we must do a remote wakeup. Its a 'light' wakeup though,
+ * since all we need to do is flip p->state to TASK_RUNNING, since
+ * the task is still ->on_rq.
+ */
+static int ttwu_remote(struct task_struct *p, int wake_flags)
+{
+	struct rq *rq;
+	int ret = 0;
+
+	rq = __task_rq_lock(p);
+	if (p->on_rq) {
+		ttwu_do_wakeup(rq, p, wake_flags);
+		ret = 1;
+	}
+	__task_rq_unlock(rq);
+
+	return ret;
+}
+
+static void ttwu_queue(struct task_struct *p, int cpu)
+{
+	struct rq *rq = cpu_rq(cpu);
+
+	raw_spin_lock(&rq->lock);
+	ttwu_do_activate(rq, p, 0);
+	raw_spin_unlock(&rq->lock);
+}
+
 /**
  * try_to_wake_up - wake up a thread
  * @p: the thread to be awakened
@@ -2492,27 +2535,25 @@ ttwu_do_wakeup(struct rq *rq, struct tas
 static int
 try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags)
 {
-	int cpu, this_cpu, success = 0;
 	unsigned long flags;
-	struct rq *rq;
-
-	this_cpu = get_cpu();
+	int cpu, success = 0;
 
 	smp_wmb();
 	raw_spin_lock_irqsave(&p->pi_lock, flags);
 	if (!(p->state & state))
 		goto out;
 
+	success = 1; /* we're going to change ->state */
 	cpu = task_cpu(p);
 
-	if (p->on_rq) {
-		rq = __task_rq_lock(p);
-		if (p->on_rq)
-			goto out_running;
-		__task_rq_unlock(rq);
-	}
+	if (p->on_rq && ttwu_remote(p, wake_flags))
+		goto stat;
 
 #ifdef CONFIG_SMP
+	/*
+	 * If the owning (remote) cpu is still in the middle of schedule() with
+	 * this task as prev, wait until its done referencing the task.
+	 */
 	while (p->on_cpu) {
 #ifdef __ARCH_WANT_INTERRUPTS_ON_CTXSW
 		/*
@@ -2521,8 +2562,10 @@ try_to_wake_up(struct task_struct *p, un
 		 * to spin on ->on_cpu if p is current, since that would
 		 * deadlock.
 		 */
-		if (p == current)
-			goto out_activate;
+		if (p == current) {
+			ttwu_queue(p, cpu);
+			goto stat;
+		}
 #endif
 		cpu_relax();
 	}
@@ -2538,33 +2581,15 @@ try_to_wake_up(struct task_struct *p, un
 		p->sched_class->task_waking(p);
 
 	cpu = select_task_rq(p, SD_BALANCE_WAKE, wake_flags);
-#ifdef __ARCH_WANT_INTERRUPTS_ON_CTXSW
-out_activate:
-#endif
-#endif /* CONFIG_SMP */
-
-	rq = cpu_rq(cpu);
-	raw_spin_lock(&rq->lock);
-
-#ifdef CONFIG_SMP
-	if (cpu != task_cpu(p))
+	if (task_cpu(p) != cpu)
 		set_task_cpu(p, cpu);
+#endif /* CONFIG_SMP */
 
-	if (p->sched_contributes_to_load)
-		rq->nr_uninterruptible--;
-#endif
-
-	activate_task(rq, p, ENQUEUE_WAKEUP | ENQUEUE_WAKING);
-	p->on_rq = 1;
-out_running:
-	ttwu_do_wakeup(rq, p, wake_flags);
-	success = 1;
-	__task_rq_unlock(rq);
-
+	ttwu_queue(p, cpu);
+stat:
 	ttwu_stat(p, cpu, wake_flags);
 out:
 	raw_spin_unlock_irqrestore(&p->pi_lock, flags);
-	put_cpu();
 
 	return success;
 }


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