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Subject[PATCH] Make highly niced processes run only when idle
This patch makes a process with nice values >= 20 (according to
setpriority(2)) completely stop when there are other runnable
processes with smaller nice values.
Try run something with `nice -n 30' (which `setpriority' to 20)

NOTE: This Patch Should Not Be Used On Production Machine Unless
You Know What You Are Doing.

Only tested on a uniprocessor PentiumII.

I don't know whether this breaks the standard, but it should
break no programs.

Applies to 2.4.16.

Note: this patch file is hand-modified from rcsdiff output.

========= cut here ==========

diff -Nur linux-2.4.16/kernel/sched.c linux/kernel/sched.c
--- linux-2.4.16/kernel/sched.c 2001/11/23 09:15:55
+++ linux/kernel/sched.c 2001/11/23 09:42:46
@@ -19,6 +19,12 @@
* current-task
*/

+/*
+ private patch by WQC: we use nice values 20 and beyond for `idle priority' processes,
+ so that they take absolutely no process time when there are higher priority processes
+ running.
+*/
+
#include <linux/config.h>
#include <linux/mm.h>
#include <linux/init.h>
@@ -68,7 +74,8 @@
#define TICK_SCALE(x) ((x) << 2)
#endif

-#define NICE_TO_TICKS(nice) (TICK_SCALE(20-(nice))+1)
+#define NICE_TO_TICKS(nice)\
+ (((nice) < 20) ? (TICK_SCALE(20-(nice))+1) : (TICK_SCALE(1)+1))


/*
@@ -150,7 +157,8 @@
* runnable process, but before the idle thread.
* Also, dont trigger a counter recalculation.
*/
- weight = -1;
+ /* If it yields, it ranks below the nicest processes */
+ weight = -999;
if (p->policy & SCHED_YIELD)
goto out;

@@ -166,9 +174,18 @@
* over..
*/
weight = p->counter;
+ /* If this is included, the oh-so-large addition below
+ will not work
+
if (!weight)
goto out;
-
+ However, to be consistent, we should give such a process a disadvantage.
+ */
+ if (! weight) {
+ if (p->nice < 20) weight = 800;
+ else if (p->nice < 27) weight = (27 - p->nice) * 100;
+ goto out;
+ }
#ifdef CONFIG_SMP
/* Give a largish advantage to the same processor... */
/* (this is equivalent to penalizing other processors) */
@@ -179,7 +196,12 @@
/* .. and a slight advantage to the current MM */
if (p->mm == this_mm || !p->mm)
weight += 1;
- weight += 20 - p->nice;
+ if (p->nice < 20)
+ weight += 800 + 20 - p->nice;
+ else if (p->nice < 27)
+ /* For super-nice ones, they are scheduled if no one else wants the CPU */
+ weight += (27 - p->nice) * 100;
+ if (weight > 999) weight = 999;
goto out;
}

@@ -537,7 +559,7 @@
struct task_struct *prev, *next, *p;
struct list_head *tmp;
int this_cpu, c;
-
+ int need_recalc;

spin_lock_prefetch(&runqueue_lock);

@@ -590,17 +612,20 @@
*/
next = idle_task(this_cpu);
c = -1000;
+ need_recalc = 0;
list_for_each(tmp, &runqueue_head) {
p = list_entry(tmp, struct task_struct, run_list);
if (can_schedule(p, this_cpu)) {
int weight = goodness(p, this_cpu, prev->active_mm);
- if (weight > c)
+ if (weight > c) {
c = weight, next = p;
+ need_recalc = (p->counter == 0);
+ }
}
}

/* Do we need to re-calculate counters? */
- if (unlikely(!c)) {
+ if (unlikely(need_recalc)) {
struct task_struct *p;

spin_unlock_irq(&runqueue_lock);
@@ -857,17 +882,17 @@
if (increment < 0) {
if (!capable(CAP_SYS_NICE))
return -EPERM;
- if (increment < -40)
- increment = -40;
+ if (increment < -50)
+ increment = -50;
}
- if (increment > 40)
- increment = 40;
+ if (increment > 50)
+ increment = 50;

newprio = current->nice + increment;
if (newprio < -20)
newprio = -20;
- if (newprio > 19)
- newprio = 19;
+ if (newprio > 29)
+ newprio = 29;
current->nice = newprio;
return 0;
}
diff -Nur linux-2.4.16/kernel/sys.c linux/kernel/sys.c
--- linux-2.4.16/kernel/sys.c 2001/11/17 11:42:42
+++ linux/kernel/sys.c 2001/11/17 11:44:50
@@ -206,8 +206,8 @@
error = -ESRCH;
if (niceval < -20)
niceval = -20;
- if (niceval > 19)
- niceval = 19;
+ if (niceval > 29)
+ niceval = 29;

read_lock(&tasklist_lock);
for_each_task(p) {
@@ -249,7 +249,7 @@
long niceval;
if (!proc_sel(p, which, who))
continue;
- niceval = 20 - p->nice;
+ niceval = 30 - p->nice;
if (niceval > retval)
retval = niceval;
}
-
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