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SubjectRe: Linux 2.4.20-pre2

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.
bhavesh@avaya.com


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;
-
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