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authorGregory Haskins <ghaskins@novell.com>2008-12-29 15:39:52 +0100
committerGregory Haskins <ghaskins@novell.com>2008-12-29 15:39:52 +0100
commit967fc04671feea4dbf780c9e55a0bc8fcf68a14e (patch)
tree223f2bb8c59138cc70fbb0e438ae27819ebe1a92 /kernel
parentsched: make double-lock-balance fair (diff)
downloadlinux-967fc04671feea4dbf780c9e55a0bc8fcf68a14e.tar.xz
linux-967fc04671feea4dbf780c9e55a0bc8fcf68a14e.zip
sched: add sched_class->needs_post_schedule() member
We currently run class->post_schedule() outside of the rq->lock, which means that we need to test for the need to post_schedule outside of the lock to avoid a forced reacquistion. This is currently not a problem as we only look at rq->rt.overloaded. However, we want to enhance this going forward to look at more state to reduce the need to post_schedule to a bare minimum set. Therefore, we introduce a new member-func called needs_post_schedule() which tests for the post_schedule condtion without actually performing the work. Therefore it is safe to call this function before the rq->lock is released, because we are guaranteed not to drop the lock at an intermediate point (such as what post_schedule() may do). We will use this later in the series [ rostedt: removed paranoid BUG_ON ] Signed-off-by: Gregory Haskins <ghaskins@novell.com>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/sched.c8
-rw-r--r--kernel/sched_rt.c24
2 files changed, 21 insertions, 11 deletions
diff --git a/kernel/sched.c b/kernel/sched.c
index 8fca364f3593..3acbad8991a2 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -2621,6 +2621,12 @@ static void finish_task_switch(struct rq *rq, struct task_struct *prev)
{
struct mm_struct *mm = rq->prev_mm;
long prev_state;
+#ifdef CONFIG_SMP
+ int post_schedule = 0;
+
+ if (current->sched_class->needs_post_schedule)
+ post_schedule = current->sched_class->needs_post_schedule(rq);
+#endif
rq->prev_mm = NULL;
@@ -2639,7 +2645,7 @@ static void finish_task_switch(struct rq *rq, struct task_struct *prev)
finish_arch_switch(prev);
finish_lock_switch(rq, prev);
#ifdef CONFIG_SMP
- if (current->sched_class->post_schedule)
+ if (post_schedule)
current->sched_class->post_schedule(rq);
#endif
diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
index 8d33843cb2c4..b0b6ea4ed674 100644
--- a/kernel/sched_rt.c
+++ b/kernel/sched_rt.c
@@ -1290,20 +1290,23 @@ static void pre_schedule_rt(struct rq *rq, struct task_struct *prev)
pull_rt_task(rq);
}
+/*
+ * assumes rq->lock is held
+ */
+static int needs_post_schedule_rt(struct rq *rq)
+{
+ return rq->rt.overloaded ? 1 : 0;
+}
+
static void post_schedule_rt(struct rq *rq)
{
/*
- * If we have more than one rt_task queued, then
- * see if we can push the other rt_tasks off to other CPUS.
- * Note we may release the rq lock, and since
- * the lock was owned by prev, we need to release it
- * first via finish_lock_switch and then reaquire it here.
+ * This is only called if needs_post_schedule_rt() indicates that
+ * we need to push tasks away
*/
- if (unlikely(rq->rt.overloaded)) {
- spin_lock_irq(&rq->lock);
- push_rt_tasks(rq);
- spin_unlock_irq(&rq->lock);
- }
+ spin_lock_irq(&rq->lock);
+ push_rt_tasks(rq);
+ spin_unlock_irq(&rq->lock);
}
/*
@@ -1557,6 +1560,7 @@ static const struct sched_class rt_sched_class = {
.rq_online = rq_online_rt,
.rq_offline = rq_offline_rt,
.pre_schedule = pre_schedule_rt,
+ .needs_post_schedule = needs_post_schedule_rt,
.post_schedule = post_schedule_rt,
.task_wake_up = task_wake_up_rt,
.switched_from = switched_from_rt,