sched: Try not to migrate higher priority RT tasks

[mv-sheeva.git] / kernel / sched_rt.c

diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
index d10c80ebb67a2821038a9c59b912bf8e323d67e3..6a02b38ab653cfc226ff96a07c5ecdd5e2a19c9f 100644 (file)
--- a/kernel/sched_rt.c
+++ b/kernel/sched_rt.c
@@ -960,18 +960,18 @@ select_task_rq_rt(struct rq *rq, struct task_struct *p, int sd_flag, int flags)
         * runqueue. Otherwise simply start this RT task
         * on its current runqueue.
         *
-        * We want to avoid overloading runqueues. Even if
-        * the RT task is of higher priority than the current RT task.
-        * RT tasks behave differently than other tasks. If
-        * one gets preempted, we try to push it off to another queue.
-        * So trying to keep a preempting RT task on the same
-        * cache hot CPU will force the running RT task to
-        * a cold CPU. So we waste all the cache for the lower
-        * RT task in hopes of saving some of a RT task
-        * that is just being woken and probably will have
-        * cold cache anyway.
+        * We want to avoid overloading runqueues. If the woken
+        * task is a higher priority, then it will stay on this CPU
+        * and the lower prio task should be moved to another CPU.
+        * Even though this will probably make the lower prio task
+        * lose its cache, we do not want to bounce a higher task
+        * around just because it gave up its CPU, perhaps for a
+        * lock?
+        *
+        * For equal prio tasks, we just let the scheduler sort it out.
         */
        if (unlikely(rt_task(rq->curr)) &&
+           rq->curr->prio < p->prio &&
            (p->rt.nr_cpus_allowed > 1)) {
                int cpu = find_lowest_rq(p);
 
@@ -1491,6 +1491,8 @@ static void task_woken_rt(struct rq *rq, struct task_struct *p)
        if (!task_running(rq, p) &&
            !test_tsk_need_resched(rq->curr) &&
            has_pushable_tasks(rq) &&
+           rt_task(rq->curr) &&
+           rq->curr->prio < p->prio &&
            p->rt.nr_cpus_allowed > 1)
                push_rt_tasks(rq);
 }