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Subject[sched] [patch] schedule-cleanup-2.5.3-pre2-A1

the attached patch speeds up and cleans up schedule(), removing the
need_reschedule check on bkl-reacquire. This was needed in 2.2 times when
the big kernel lock was still prominent, but today it's not needed
anymore, especially with the preemption/lowlatency patches that will do
this correctly. This change removes 5 lines from the source code, and a
number of instructions from the scheduler hotpath. (i've also reverted the
switch statement's indentation to the previous, more correct indentation
style.)

Ingo
--- linux/kernel/sched.c.orig Sun Jan 20 11:47:39 2002
+++ linux/kernel/sched.c Sun Jan 20 11:47:53 2002
@@ -589,29 +589,26 @@
*/
asmlinkage void schedule(void)
{
- task_t *prev, *next;
+ task_t *prev = current, *next;
+ runqueue_t *rq = this_rq();
prio_array_t *array;
- runqueue_t *rq;
list_t *queue;
int idx;

if (unlikely(in_interrupt()))
BUG();
-need_resched_back:
- prev = current;
release_kernel_lock(prev, smp_processor_id());
- rq = this_rq();
spin_lock_irq(&rq->lock);

switch (prev->state) {
- case TASK_INTERRUPTIBLE:
- if (unlikely(signal_pending(prev))) {
- prev->state = TASK_RUNNING;
- break;
- }
- default:
- deactivate_task(prev, rq);
- case TASK_RUNNING:
+ case TASK_INTERRUPTIBLE:
+ if (unlikely(signal_pending(prev))) {
+ prev->state = TASK_RUNNING;
+ break;
+ }
+ default:
+ deactivate_task(prev, rq);
+ case TASK_RUNNING:
}
pick_next_task:
if (unlikely(!rq->nr_running)) {
@@ -654,8 +651,6 @@
spin_unlock_irq(&rq->lock);

reacquire_kernel_lock(current);
- if (need_resched())
- goto need_resched_back;
return;
}
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