sched: Restructure ttwu() some more
Peter Zijlstra [Tue, 5 Apr 2011 15:23:57 +0000 (17:23 +0200)]
Factor our helper functions to make the inner workings of try_to_wake_up()
more obvious, this also allows for adding remote queues.

Reviewed-by: Frank Rowand <frank.rowand@am.sony.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Nick Piggin <npiggin@kernel.dk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/20110405152729.475848012@chello.nl

kernel/sched.c

index e309dba..7d8b85f 100644 (file)
@@ -2483,6 +2483,48 @@ ttwu_do_wakeup(struct rq *rq, struct task_struct *p, int wake_flags)
 #endif
 }
 
+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
+
+       ttwu_activate(rq, p, ENQUEUE_WAKEUP | ENQUEUE_WAKING);
+       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
@@ -2501,27 +2543,25 @@ ttwu_do_wakeup(struct rq *rq, struct task_struct *p, int wake_flags)
 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
                /*
@@ -2530,8 +2570,10 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags)
                 * 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();
        }
@@ -2547,32 +2589,15 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags)
                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
-
-       ttwu_activate(rq, p, ENQUEUE_WAKEUP | ENQUEUE_WAKING);
-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;
 }