Re: Linux 2.4.20-pre2

[Bhavesh P. Davda]

For the Nth time, here again is the patch for fixing the scheduler for
correct SCHED_FIFO and SCHED_RR behaviour.

I waited to see it in 2.4.20-pre1, not there, 2.4.20-pre2, not there...

Please apply it in 2.4.20-pre3

Thanks

- Bhavesh
-- 
Bhavesh P. Davda
Avaya Inc.
[e-mail]

diff -aur linux-2.4.19/kernel/sched.c linux-2.4.19-sched/kernel/sched.c
--- linux-2.4.19/kernel/sched.c	Tue Aug  6 11:37:49 2002
+++ linux-2.4.19-sched/kernel/sched.c	Tue Aug  6 13:42:20 2002
@@ -318,13 +318,17 @@
 /*
  * Careful!
  *
- * This has to add the process to the _beginning_ of the
- * run-queue, not the end. See the comment about "This is
- * subtle" in the scheduler proper..
+ * This has to add the process to the _end_ of the 
+ * run-queue, not the beginning. The goodness value will
+ * determine whether this process will run next. This is
+ * important to get SCHED_FIFO and SCHED_RR right, where
+ * a process that is either pre-empted or its time slice
+ * has expired, should be moved to the tail of the run 
+ * queue for its priority - Bhavesh Davda
  */
 static inline void add_to_runqueue(struct task_struct * p)
 {
-	list_add(&p->run_list, &runqueue_head);
+	list_add_tail(&p->run_list, &runqueue_head);
 	nr_running++;
 }
 
@@ -334,12 +338,6 @@
 	list_add_tail(&p->run_list, &runqueue_head);
 }
 
-static inline void move_first_runqueue(struct task_struct * p)
-{
-	list_del(&p->run_list);
-	list_add(&p->run_list, &runqueue_head);
-}
-
 /*
  * Wake up a process. Put it on the run-queue if it's not
  * already there.  The "current" process is always on the
@@ -955,8 +953,6 @@
 	retval = 0;
 	p->policy = policy;
 	p->rt_priority = lp.sched_priority;
-	if (task_on_runqueue(p))
-		move_first_runqueue(p);
 
 	current->need_resched = 1;
 
diff -aur linux-2.4.19/kernel/timer.c linux-2.4.19-sched/kernel/timer.c
--- linux-2.4.19/kernel/timer.c	Tue Aug  6 11:37:49 2002
+++ linux-2.4.19-sched/kernel/timer.c	Tue Aug  6 13:42:20 2002
@@ -601,7 +601,14 @@
 	if (p->pid) {
 		if (--p->counter <= 0) {
 			p->counter = 0;
-			p->need_resched = 1;
+			/*
+			 * SCHED_FIFO is priority preemption, so this is 
+			 * not the place to decide whether to reschedule a
+			 * SCHED_FIFO task or not - Bhavesh Davda
+			 */
+			if (p->policy != SCHED_FIFO) {
+				p->need_resched = 1;
+			}
 		}
 		if (p->nice > 0)
 			kstat.per_cpu_nice[cpu] += user_tick;