[PATCH 14/22] sched: Drop rq->lock from first part of wake_up_new_task()

Peter Zijlstra
2011-03-02T17:46:54Z

[-- Attachment #1: sched-wunt.patch --]
[-- Type: text/plain, Size: 1619 bytes --]

Since p->pi_lock now protects all things needed to call
select_task_rq() avoid the double remote rq->lock acquisition and rely
on p->pi_lock.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <new-submission>
---
kernel/sched.c | 17 +++--------------
1 file changed, 3 insertions(+), 14 deletions(-)

Index: linux-2.6/kernel/sched.c
===================================================================
--- linux-2.6.orig/kernel/sched.c
+++ linux-2.6/kernel/sched.c
@@ -2726,28 +2726,18 @@ void wake_up_new_task(struct task_struct
{
unsigned long flags;
struct rq *rq;
- int cpu __maybe_unused = get_cpu();

+ raw_spin_lock_irqsave(&p->pi_lock, flags);
#ifdef CONFIG_SMP
- rq = task_rq_lock(p, &flags);
- p->state = TASK_WAKING;
-
/*
* Fork balancing, do it here and not earlier because:
* - cpus_allowed can change in the fork path
* - any previously selected cpu might disappear through hotplug
- *
- * We set TASK_WAKING so that select_task_rq() can drop rq->lock
- * without people poking at ->cpus_allowed.
*/
- cpu = select_task_rq(p, SD_BALANCE_FORK, 0);
- set_task_cpu(p, cpu);
-
- p->state = TASK_RUNNING;
- task_rq_unlock(rq, p, &flags);
+ set_task_cpu(p, select_task_rq(p, SD_BALANCE_FORK, 0));
#endif

- rq = task_rq_lock(p, &flags);
+ rq = __task_rq_lock(p);
activate_task(rq, p, 0);
trace_sched_wakeup_new(p, true);
check_preempt_curr(rq, p, WF_FORK);
@@ -2756,7 +2746,6 @@ void wake_up_new_task(struct task_struct
p->sched_class->task_woken(rq, p);
#endif
task_rq_unlock(rq, p, &flags);
- put_cpu();
}

#ifdef CONFIG_PREEMPT_NOTIFIERS