[PATCH 19/22] sched: Restructure ttwu some more

Peter Zijlstra
2011-03-02T17:49:06Z

[-- Attachment #1: sched-ttwu-foo.patch --]
[-- Type: text/plain, Size: 3241 bytes --]

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

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <new-submission>
---
kernel/sched.c | 83 +++++++++++++++++++++++++++++++++++++--------------------
1 file changed, 55 insertions(+), 28 deletions(-)

Index: linux-2.6/kernel/sched.c
===================================================================
--- linux-2.6.orig/kernel/sched.c
+++ linux-2.6/kernel/sched.c
@@ -2475,6 +2475,48 @@ 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);
+ 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
@@ -2493,27 +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
/*
@@ -2539,30 +2579,17 @@ 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);
-out_activate:
-#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);

- if (p->sched_contributes_to_load)
- rq->nr_uninterruptible--;
-#endif
-
- activate_task(rq, p, ENQUEUE_WAKEUP | ENQUEUE_WAKING);
-out_running:
- ttwu_do_wakeup(rq, p, wake_flags);
- success = 1;
- __task_rq_unlock(rq);
+out_activate:
+#endif /* CONFIG_SMP */

+ ttwu_queue(p, cpu);
+stat:
ttwu_stat(p, cpu, wake_flags);
out:
raw_spin_unlock_irqrestore(&p->pi_lock, flags);
- put_cpu();

return success;
}