[(RESEND) PATCH] sched: fix RT task-wakeup logic

Gregory Haskins
2008-04-28T17:03:47Z

Hi Ingo,
Im not sure if this patch fell through the cracks, or if you didn't like it
for some reason. If you can, please ACK/NACK it so I know if you have
reviewed it or not. Thanks!

(This applies to sched-devel, and should be considered a bug fix for 25.y and
the 26 merge window)

-Greg

------------------------------
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>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Acked-by: Dmitry Adamushko <dmitry.adamushko@gmail.com>
CC: Ingo Molnar <mingo@elte.hu>
---

include/linux/sched.h | 7 ++++++-
kernel/sched_rt.c | 7 +++++--
2 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 949bd54..55d4bd4 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1966,6 +1966,11 @@ static inline void clear_tsk_need_resched(struct task_struct *tsk)
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));
@@ -1980,7 +1985,7 @@ static inline int fatal_signal_pending(struct task_struct *p)

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 79e5ad5..ae6b0e6 100644
--- a/kernel/sched_rt.c
+++ b/kernel/sched_rt.c
@@ -1058,11 +1058,14 @@ static void post_schedule_rt(struct rq *rq)
}
}

-
+/*
+ * 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);
}