[PATCH] O4int interactivity

[Con Kolivas]

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Here is a diff against the O3int patch in 2.5.74-mm3 trying to decrease aud=
io=20
skips and improve X smoothness.

It is easier to become interactive with this one to try and decrease=20
application startup and wakeup time, while hopefully still preventing cpu=20
hogs from starving the machine.

Changes:
Child penalty increased to 95 as in early 2.5 O(1) implementations. This fi=
xes=20
the "parent spinning madly waiting for child to spawn and in the process it=
=20
is the parent that starves the child"; 80 wasn't enough.

The sleep buffer has returned much smaller currently set at 50ms which=20
prevents fully interactive tasks from dropping down a priority for short=20
bursts of cpu activity (eg X).

Idle tasks now get a small priority boost so they "rest" at a dynamic prior=
ity=20
just below interactive. They now wake up to an interactive state more=20
rapidly, and spawn more interactive children.

The variable boost when a process has been running less than MAX_SLEEP_AVG =
has=20
been tweaked and consequently is more aggressive.

Slight code rearrangement to have one less if.. branch.

Also available for download here:
http://kernel.kolivas.org/2.5

Con
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--- linux-2.5.74-mm3/kernel/sched.c	2003-07-10 10:23:14.000000000 +1000
+++ linux-2.5.74-test/kernel/sched.c	2003-07-10 10:41:57.000000000 +1000
@@ -68,7 +68,7 @@
  */
 #define MIN_TIMESLICE		( 10 * HZ / 1000)
 #define MAX_TIMESLICE		(200 * HZ / 1000)
-#define CHILD_PENALTY		80
+#define CHILD_PENALTY		95
 #define PARENT_PENALTY		100
 #define EXIT_WEIGHT		3
 #define PRIO_BONUS_RATIO	25
@@ -76,6 +76,7 @@
 #define MIN_SLEEP_AVG		(HZ)
 #define MAX_SLEEP_AVG		(10*HZ)
 #define STARVATION_LIMIT	(10*HZ)
+#define SLEEP_BUFFER		(HZ/20)
 #define NODE_THRESHOLD		125
 #define MAX_BONUS		((MAX_USER_PRIO - MAX_RT_PRIO) * PRIO_BONUS_RATIO / 100)
 
@@ -392,33 +393,42 @@ static inline void activate_task(task_t 
 		unsigned long runtime = jiffies - p->avg_start;
 
 		/*
-		 * This code gives a bonus to interactive tasks.
-		 *
-		 * The boost works by updating the 'average sleep time'
-		 * value here, based on ->last_run. The more time a task
-		 * spends sleeping, the higher the average gets - and the
-		 * higher the priority boost gets as well.
-		 */
-		p->sleep_avg += sleep_time;
-		/*
-		 * Give a bonus to tasks that wake early on to prevent
-		 * the problem of the denominator in the bonus equation
-		 * from continually getting larger.
-		 */
-		if (runtime < MAX_SLEEP_AVG)
-			p->sleep_avg += (runtime - p->sleep_avg) * (MAX_SLEEP_AVG - runtime) *
-				(MAX_BONUS - INTERACTIVE_DELTA) / MAX_BONUS / MAX_SLEEP_AVG;
-
-		if (p->sleep_avg > MAX_SLEEP_AVG)
-			p->sleep_avg = MAX_SLEEP_AVG;
-
-		/*
 		 * Tasks that sleep a long time are categorised as idle and
-		 * get their static priority only
+		 * will get just under interactive status with a small runtime
+		 * to allow them to become interactive or non-interactive rapidly
 		 */
 		if (sleep_time > MIN_SLEEP_AVG){
 			p->avg_start = jiffies - MIN_SLEEP_AVG;
-			p->sleep_avg = MIN_SLEEP_AVG / 2;
+			p->sleep_avg = MIN_SLEEP_AVG * (MAX_BONUS - INTERACTIVE_DELTA - 1) /
+				MAX_BONUS;
+		} else {
+			/*
+			 * This code gives a bonus to interactive tasks.
+			 *
+			 * The boost works by updating the 'average sleep time'
+			 * value here, based on ->last_run. The more time a task
+			 * spends sleeping, the higher the average gets - and the
+			 * higher the priority boost gets as well.
+			 */
+			p->sleep_avg += sleep_time;
+
+			/*
+			 * Give a bonus to tasks that wake early on to prevent
+			 * the problem of the denominator in the bonus equation
+			 * from continually getting larger.
+			 */
+			if ((runtime - MIN_SLEEP_AVG) < MAX_SLEEP_AVG)
+				p->sleep_avg += (runtime - p->sleep_avg) *
+					(MAX_SLEEP_AVG + MIN_SLEEP_AVG - runtime) *
+					(MAX_BONUS - INTERACTIVE_DELTA) / MAX_BONUS / MAX_SLEEP_AVG;
+
+			/*
+			 * Keep a small buffer of SLEEP_BUFFER sleep_avg to
+			 * prevent fully interactive tasks from becoming
+			 * lower priority with small bursts of cpu usage.
+			 */
+			if (p->sleep_avg > (MAX_SLEEP_AVG + SLEEP_BUFFER))
+				p->sleep_avg = MAX_SLEEP_AVG + SLEEP_BUFFER;
 		}
 
 		if (unlikely(p->avg_start > jiffies)){

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