Re: web page on O(1) scheduler

[Mike Galbraith <efault@gmx.de>]

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At 11:26 AM 5/21/2003 +0200, Mike Galbraith wrote:

>Try the attached overly simplistic (KISS:) diff, and watch your starvation 
>issues be very noticably reduced.

Ahem ;-)

Now even attached.

         -Mike 

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--- linux-2.5.69/kernel/sched.c.org	Wed May 21 07:45:00 2003
+++ linux-2.5.69/kernel/sched.c	Wed May 21 08:27:09 2003
@@ -1264,7 +1264,7 @@
 	task_t *prev, *next;
 	runqueue_t *rq;
 	prio_array_t *array;
-	struct list_head *queue;
+	struct list_head *head, *curr;
 	int idx;
 
 	/*
@@ -1331,8 +1331,22 @@
 	}
 
 	idx = sched_find_first_bit(array->bitmap);
-	queue = array->queue + idx;
-	next = list_entry(queue->next, task_t, run_list);
+next_queue:
+	head = array->queue + idx;
+	curr = head->next;
+	next = list_entry(curr, task_t, run_list);
+	curr = curr->next;
+	/*
+	 * If we are about to wrap back to the head of the queue,
+	 * give a lower priority queue a chance to sneak one in.
+	 */
+	if (idx == prev->prio && curr == head && array->nr_active > 1) {
+		int tmp = find_next_bit(array->bitmap, MAX_PRIO, ++idx);
+		if (tmp < MAX_PRIO) {
+			idx = tmp;
+			goto next_queue;
+		}
+	}
 
 switch_tasks:
 	prefetch(next);