Re: must-fix list for 2.6.0

[Mike Galbraith <efault@gmx.de>]

[-- Attachment #1: Type: text/plain, Size: 864 bytes --]

At 05:21 AM 5/1/2003 +0200, Mike Galbraith wrote:
>At 12:11 PM 4/30/2003 -0700, Andrew Morton wrote:
>>Maciej Soltysiak <solt@dns.toxicfilms.tv> wrote:
>> >
>> >
>> > Also there is one issue, i am not sure if this may be a kernel issue,
>> > but with setiathome running in a X desktop environment all apps work fine,
>> > but when i run openoffice, openoffice responds with 5 second delay.
>>
>>That'll be the changed sched_yield() semantics.
>>
>>The below patch should fix that up, but we need to decide whether the (rather
>>unclear) advantages of the sched_yield() change outweigh the breakage which
>>it caused linuxthreads applications.

<snip>

Anyway, attached is a patchlet that works for me if anyone wants to try 
it.  I removed printk's, and whatnot but it'll have some offsets because of 
other butchery in my X-para-mental tree ;-)

         -Mike   

[-- Attachment #2: yield.diff --]
[-- Type: application/octet-stream, Size: 1541 bytes --]

--- kernel/sched.c.org	Fri Apr 25 06:24:34 2003
+++ kernel/sched.c	Thu May  1 07:38:00 2003
@@ -1265,7 +1323,7 @@
 	runqueue_t *rq;
 	prio_array_t *array;
 	struct list_head *queue;
-	int idx;
+	int idx = 0;
 
 	/*
 	 * Test if we are atomic.  Since do_exit() needs to call into
@@ -1330,7 +1388,19 @@
 		rq->expired_timestamp = 0;
 	}
 
-	idx = sched_find_first_bit(array->bitmap);
+	if (!idx || idx >= MAX_PRIO)
+		idx = sched_find_first_bit(array->bitmap);
+	else {
+		idx = find_next_bit(array->bitmap, MAX_PRIO, idx + 1);
+		if (idx >= MAX_PRIO) {
+			idx = 0;
+			spin_unlock_irq(&rq->lock);
+			reacquire_kernel_lock(current);
+			preempt_enable_no_resched();
+			goto need_resched;
+		}
+	}
+
 	queue = array->queue + idx;
 	next = list_entry(queue->next, task_t, run_list);
 
@@ -1984,19 +2054,12 @@
 	prio_array_t *array = current->array;
 
 	/*
-	 * We implement yielding by moving the task into the expired
-	 * queue.
-	 *
-	 * (special rule: RT tasks will just roundrobin in the active
-	 *  array.)
+	 * We implement yielding by moving the task to the back of
+	 * the queue.
 	 */
-	if (likely(!rt_task(current))) {
-		dequeue_task(current, array);
-		enqueue_task(current, rq->expired);
-	} else {
-		list_del(&current->run_list);
-		list_add_tail(&current->run_list, array->queue + current->prio);
-	}
+	list_del(&current->run_list);
+	list_add_tail(&current->run_list, array->queue + current->prio);
+	set_tsk_need_resched(current);
 	/*
 	 * Since we are going to call schedule() anyway, there's
 	 * no need to preempt: