From: Ingo Molnar <mingo@elte.hu>
Change the order of tasks to be moved.
This and the following patch will need more testing on big systems where it
could hurt, but for now I guess it can go in.
Breaking these out just makes them easier for people to test.
---
25-akpm/kernel/sched.c | 42 ++++++++++++++++++++++++++----------------
1 files changed, 26 insertions(+), 16 deletions(-)
diff -puN kernel/sched.c~sched-move-cold-task kernel/sched.c
--- 25/kernel/sched.c~sched-move-cold-task 2004-04-05 18:45:30.816526744 -0700
+++ 25-akpm/kernel/sched.c 2004-04-05 18:45:30.824525528 -0700
@@ -331,6 +331,21 @@ static void enqueue_task(struct task_str
p->array = array;
}
+#ifdef CONFIG_SMP
+/*
+ * Used by the migration code - we pull tasks from the head of the
+ * remote queue so we want these tasks to show up at the head of the
+ * local queue:
+ */
+static inline void enqueue_task_head(struct task_struct *p, prio_array_t *array)
+{
+ list_add(&p->run_list, array->queue + p->prio);
+ __set_bit(p->prio, array->bitmap);
+ array->nr_active++;
+ p->array = array;
+}
+#endif
+
/*
* effective_prio - return the priority that is based on the static
* priority but is modified by bonuses/penalties.
@@ -1262,7 +1277,7 @@ void pull_task(runqueue_t *src_rq, prio_
src_rq->nr_running--;
set_task_cpu(p, this_cpu);
this_rq->nr_running++;
- enqueue_task(p, this_array);
+ enqueue_task_head(p, this_array);
p->timestamp = sched_clock() -
(src_rq->timestamp_last_tick - p->timestamp);
/*
@@ -1320,18 +1335,13 @@ static int move_tasks(runqueue_t *this_r
if (max_nr_move <= 0 || busiest->nr_running <= 1)
goto out;
- /*
- * We first consider expired tasks. Those will likely not be
- * executed in the near future, and they are most likely to
- * be cache-cold, thus switching CPUs has the least effect
- * on them.
- */
- if (busiest->expired->nr_active) {
- array = busiest->expired;
- dst_array = this_rq->expired;
- } else {
+ /* We first consider active tasks. */
+ if (busiest->active->nr_active) {
array = busiest->active;
dst_array = this_rq->active;
+ } else {
+ array = busiest->expired;
+ dst_array = this_rq->expired;
}
new_array:
@@ -1343,20 +1353,20 @@ skip_bitmap:
else
idx = find_next_bit(array->bitmap, MAX_PRIO, idx);
if (idx >= MAX_PRIO) {
- if (array == busiest->expired && busiest->active->nr_active) {
- array = busiest->active;
- dst_array = this_rq->active;
+ if (array == busiest->active && busiest->expired->nr_active) {
+ array = busiest->expired;
+ dst_array = this_rq->expired;
goto new_array;
}
goto out;
}
head = array->queue + idx;
- curr = head->prev;
+ curr = head->next;
skip_queue:
tmp = list_entry(curr, task_t, run_list);
- curr = curr->prev;
+ curr = curr->next;
if (!can_migrate_task(tmp, busiest, this_cpu, sd, idle)) {
if (curr != head)
_