sched: Drop the rq argument to sched_class::select_task_rq()
In preparation of calling select_task_rq() without rq->lock held, drop
the dependency on the rq argument.
Reviewed-by: Frank Rowand <frank.rowand@am.sony.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
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>
Link: http://lkml.kernel.org/r/20110405152729.031077745@chello.nl
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
index 9ca4f5f..19ecb31 100644
--- a/kernel/sched_rt.c
+++ b/kernel/sched_rt.c
@@ -977,13 +977,23 @@
static int find_lowest_rq(struct task_struct *task);
static int
-select_task_rq_rt(struct rq *rq, struct task_struct *p, int sd_flag, int flags)
+select_task_rq_rt(struct task_struct *p, int sd_flag, int flags)
{
+ struct task_struct *curr;
+ struct rq *rq;
+ int cpu;
+
if (sd_flag != SD_BALANCE_WAKE)
return smp_processor_id();
+ cpu = task_cpu(p);
+ rq = cpu_rq(cpu);
+
+ rcu_read_lock();
+ curr = ACCESS_ONCE(rq->curr); /* unlocked access */
+
/*
- * If the current task is an RT task, then
+ * If the current task on @p's runqueue is an RT task, then
* try to see if we can wake this RT task up on another
* runqueue. Otherwise simply start this RT task
* on its current runqueue.
@@ -997,21 +1007,25 @@
* lock?
*
* For equal prio tasks, we just let the scheduler sort it out.
- */
- if (unlikely(rt_task(rq->curr)) &&
- (rq->curr->rt.nr_cpus_allowed < 2 ||
- rq->curr->prio < p->prio) &&
- (p->rt.nr_cpus_allowed > 1)) {
- int cpu = find_lowest_rq(p);
-
- return (cpu == -1) ? task_cpu(p) : cpu;
- }
-
- /*
+ *
* Otherwise, just let it ride on the affined RQ and the
* post-schedule router will push the preempted task away
+ *
+ * This test is optimistic, if we get it wrong the load-balancer
+ * will have to sort it out.
*/
- return task_cpu(p);
+ if (curr && unlikely(rt_task(curr)) &&
+ (curr->rt.nr_cpus_allowed < 2 ||
+ curr->prio < p->prio) &&
+ (p->rt.nr_cpus_allowed > 1)) {
+ int target = find_lowest_rq(p);
+
+ if (target != -1)
+ cpu = target;
+ }
+ rcu_read_unlock();
+
+ return cpu;
}
static void check_preempt_equal_prio(struct rq *rq, struct task_struct *p)
