From: Con Kolivas <kernel@kolivas.org>
To: linux kernel mailing list <linux-kernel@vger.kernel.org>
Subject: [PATCH] O6int for interactivity
Date: Thu, 17 Jul 2003 00:30:25 +1000
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Cc: Andrew Morton <akpm@osdl.org>,
       Felipe Alfaro Solana <felipe_alfaro@linuxmail.org>,
       Zwane Mwaikambo <zwane@arm.linux.org.uk>
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O*int patches trying to improve the interactivity of the 2.5/6 scheduler for 
desktops. It appears possible to do this without moving to nanosecond 
resolution.

This one makes a massive difference... Please test this to death.

Changes:
The big change is in the way sleep_avg is incremented. Any amount of sleep 
will now raise you by at least one priority with each wakeup. This causes 
massive differences to startup time, extremely rapid conversion to interactive 
state, and recovery from non-interactive state rapidly as well (prevents X 
stalling after thrashing around under high loads for many seconds).

The sleep buffer was dropped to just 10ms. This has the effect of causing mild 
round robinning of very interactive tasks if they run for more than 10ms. The 
requeuing was changed from (unlikely()) to an ordinary if.. branch as this 
will be hit much more now.

MAX_BONUS as a #define was made easier to understand

Idle tasks were made slightly less interactive to prevent cpu hogs from 
becoming interactive on their very first wakeup.

Con

This patch-O6int-0307170012 applies on top of 2.6.0-test1-mm1 and can be found 
here:
http://kernel.kolivas.org/2.5

and here:

--- linux-2.6.0-test1-mm1/kernel/sched.c	2003-07-16 20:27:32.000000000 +1000
+++ linux-2.6.0-testck1/kernel/sched.c	2003-07-17 00:13:24.000000000 +1000
@@ -76,9 +76,9 @@
 #define MIN_SLEEP_AVG		(HZ)
 #define MAX_SLEEP_AVG		(10*HZ)
 #define STARVATION_LIMIT	(10*HZ)
-#define SLEEP_BUFFER		(HZ/20)
+#define SLEEP_BUFFER		(HZ/100)
 #define NODE_THRESHOLD		125
-#define MAX_BONUS		((MAX_USER_PRIO - MAX_RT_PRIO) * PRIO_BONUS_RATIO / 100)
+#define MAX_BONUS		(40 * PRIO_BONUS_RATIO / 100)
 
 /*
  * If a task is 'interactive' then we reinsert it in the active
@@ -399,7 +399,7 @@ static inline void activate_task(task_t 
 		 */
 		if (sleep_time > MIN_SLEEP_AVG){
 			p->avg_start = jiffies - MIN_SLEEP_AVG;
-			p->sleep_avg = MIN_SLEEP_AVG * (MAX_BONUS - INTERACTIVE_DELTA - 1) /
+			p->sleep_avg = MIN_SLEEP_AVG * (MAX_BONUS - INTERACTIVE_DELTA - 2) /
 				MAX_BONUS;
 		} else {
 			/*
@@ -413,14 +413,10 @@ static inline void activate_task(task_t 
 			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.
+			 * Processes that sleep get pushed to a higher priority
+			 * each time they sleep
 			 */
-			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;
+			p->sleep_avg = (p->sleep_avg * MAX_BONUS / runtime + 1) * runtime / MAX_BONUS;
 
 			/*
 			 * Keep a small buffer of SLEEP_BUFFER sleep_avg to
@@ -1311,7 +1307,7 @@ void scheduler_tick(int user_ticks, int 
 			enqueue_task(p, rq->expired);
 		} else
 			enqueue_task(p, rq->active);
-	} else if (unlikely(p->prio < effective_prio(p))){
+	} else if (p->prio < effective_prio(p)){
 		/*
 		 * Tasks that have lowered their priority are put to the end
 		 * of the active array with their remaining timeslice

-
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