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Subject[PATCH] 2.4.18 scheduler bugs
Date
Hi Marcelo et all,
The following fixes some rather straightforward bugs in the old
(pre-O(1)) scheduler that I discovered while exercising it with
custom instrumentation written in. These may be worth fixing, given
that it may be a long time before the new O(1) scheduler officially
shows up in a production tree.

Joe

- ksoftirqd() - change daemon nice(2) value from 19 to -19.

SoftIRQ servicing was less important than the most lowly of batch
tasks. This patch makes it more important than all but the realtime
tasks.

- reschedule_idle() - smp_send_reschedule when setting idle's need_resched

Idle tasks nowdays don't spin waiting for need->resched to change,
they sleep on a halt insn instead. Therefore any setting of
need->resched on an idle task running on a remote CPU should be
accompanied by a cross-processor interrupt.

diff -Nur linux-2.4.18-base/kernel/sched.c linux/kernel/sched.c
--- linux-2.4.18-base/kernel/sched.c Fri Dec 21 12:42:04 2001
+++ linux/kernel/sched.c Fri Mar 15 14:57:21 2002
@@ -225,16 +225,9 @@
if (can_schedule(p, best_cpu)) {
tsk = idle_task(best_cpu);
if (cpu_curr(best_cpu) == tsk) {
- int need_resched;
send_now_idle:
- /*
- * If need_resched == -1 then we can skip sending
- * the IPI altogether, tsk->need_resched is
- * actively watched by the idle thread.
- */
- need_resched = tsk->need_resched;
tsk->need_resched = 1;
- if ((best_cpu != this_cpu) && !need_resched)
+ if (best_cpu != this_cpu)
smp_send_reschedule(best_cpu);
return;
}
diff -Nur linux-2.4.18-base/kernel/softirq.c linux/kernel/softirq.c
--- linux-2.4.18-base/kernel/softirq.c Wed Oct 31 13:26:02 2001
+++ linux/kernel/softirq.c Fri Mar 15 14:55:38 2002
@@ -365,7 +365,7 @@
int cpu = cpu_logical_map(bind_cpu);

daemonize();
- current->nice = 19;
+ current->nice = -19;
sigfillset(&current->blocked);

/* Migrate to the right CPU */
-
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