sched/rt: Clean up check_preempt_equal_prio()

This patch checks if current can be pushed/pulled somewhere else
in advance to make logic clear, the same behavior as dl class.

- If current can't be migrated, useless to reschedule, let's hope
  task can move out.
- If task is migratable, so let's not schedule it and see if it
  can be pushed or pulled somewhere else.

Signed-off-by: Wanpeng Li <wanpeng.li@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Juri Lelli <juri.lelli@arm.com>
Cc: Kirill Tkhai <ktkhai@parallels.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1414708776-124078-1-git-send-email-wanpeng.li@linux.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index d024e6c..3d14312 100644 (file)
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -1351,16 +1351,22 @@ out:
 
 static void check_preempt_equal_prio(struct rq *rq, struct task_struct *p)
 {
-       if (rq->curr->nr_cpus_allowed == 1)
+       /*
+        * Current can't be migrated, useless to reschedule,
+        * let's hope p can move out.
+        */
+       if (rq->curr->nr_cpus_allowed == 1 ||
+           !cpupri_find(&rq->rd->cpupri, rq->curr, NULL))
                return;
 
+       /*
+        * p is migratable, so let's not schedule it and
+        * see if it is pushed or pulled somewhere else.
+        */
        if (p->nr_cpus_allowed != 1
            && cpupri_find(&rq->rd->cpupri, p, NULL))
                return;
 
-       if (!cpupri_find(&rq->rd->cpupri, rq->curr, NULL))
-               return;
-
        /*
         * There appears to be other cpus that can accept
         * current and none to run 'p', so lets reschedule