[test-PATCH] Re: [QUESTION] 2.4.x nice level

Rik van Riel
2001-04-11T10:37:29Z

On Tue, 10 Apr 2001, Rik van Riel wrote:

> I'll try to come up with a recalculation change that will make
> this thing behave better, while still retaining the short time
> slices for multiple normal-priority tasks and the cache footprint
> schedule() and friends currently have...

OK, here it is. It's nothing like montavista's singing-dancing
scheduler patch that does all, just a really minimal change that
should stretch the nice levels to yield the following CPU usage:

Nice 0 5 10 15 19
%CPU 100 56 25 6 1

Note that the code doesn't change the actual scheduling code,
just the recalculation. Care has also been taken to not increase
the cache footprint of the scheduling and recalculation code.

I'd love to hear some test results from people who are interested
in wider nice levels. How does this run on your system? Can you
trigger bad behaviour in any way?

regards,

Rik
--
Virtual memory is like a game you can't win;
However, without VM there's truly nothing to lose...

http://www.surriel.com/
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--- linux-2.4.3-ac4/kernel/sched.c.orig Tue Apr 10 21:04:06 2001
+++ linux-2.4.3-ac4/kernel/sched.c Wed Apr 11 06:18:46 2001
@@ -686,8 +686,26 @@
struct task_struct *p;
spin_unlock_irq(&runqueue_lock);
read_lock(&tasklist_lock);
- for_each_task(p)
+ for_each_task(p) {
+ if (p->nice <= 0) {
+ /* The normal case... */
p->counter = (p->counter >> 1) + NICE_TO_TICKS(p->nice);
+ } else {
+ /*
+ * Niced tasks get less CPU less often, leading to
+ * the following distribution of CPU time:
+ *
+ * Nice 0 5 10 15 19
+ * %CPU 100 56 25 6 1
+ */
+ short prio = 20 - p->nice;
+ p->nice_calc += prio;
+ if (p->nice_calc >= 20) {
+ p->nice_calc -= 20;
+ p->counter = (p->counter >> 1) + NICE_TO_TICKS(p->nice);
+ }
+ }
+ }
read_unlock(&tasklist_lock);
spin_lock_irq(&runqueue_lock);
}
--- linux-2.4.3-ac4/include/linux/sched.h.orig Tue Apr 10 21:04:13 2001
+++ linux-2.4.3-ac4/include/linux/sched.h Wed Apr 11 06:26:47 2001
@@ -303,7 +303,8 @@
* the goodness() loop in schedule().
*/
long counter;
- long nice;
+ short nice_calc;
+ short nice;
unsigned long policy;
struct mm_struct *mm;
int has_cpu, processor;