sched: fix RT task-wakeup logic
Dmitry Adamushko pointed out a logic error in task_wake_up_rt() where we
will always evaluate to "true". You can find the thread here:
http://lkml.org/lkml/2008/4/22/296
In reality, we only want to try to push tasks away when a wake up request is
not going to preempt the current task. So lets fix it.
Note: We introduce test_tsk_need_resched() instead of open-coding the flag
check so that the merge-conflict with -rt should help remind us that we
may need to support NEEDS_RESCHED_DELAYED in the future, too.
Signed-off-by: Gregory Haskins <ghaskins@novell.com>
CC: Dmitry Adamushko <dmitry.adamushko@gmail.com>
CC: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 03c2380..698b5a4 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1977,6 +1977,11 @@
clear_tsk_thread_flag(tsk,TIF_NEED_RESCHED);
}
+static inline int test_tsk_need_resched(struct task_struct *tsk)
+{
+ return unlikely(test_tsk_thread_flag(tsk,TIF_NEED_RESCHED));
+}
+
static inline int signal_pending(struct task_struct *p)
{
return unlikely(test_tsk_thread_flag(p,TIF_SIGPENDING));
@@ -1991,7 +1996,7 @@
static inline int need_resched(void)
{
- return unlikely(test_thread_flag(TIF_NEED_RESCHED));
+ return unlikely(test_tsk_need_resched(current));
}
/*
diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
index dcd6495..060e87b 100644
--- a/kernel/sched_rt.c
+++ b/kernel/sched_rt.c
@@ -1098,11 +1098,14 @@
}
}
-
+/*
+ * If we are not running and we are not going to reschedule soon, we should
+ * try to push tasks away now
+ */
static void task_wake_up_rt(struct rq *rq, struct task_struct *p)
{
if (!task_running(rq, p) &&
- (p->prio >= rq->rt.highest_prio) &&
+ !test_tsk_need_resched(rq->curr) &&
rq->rt.overloaded)
push_rt_tasks(rq);
}