1 files changed, 27 insertions, 25 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index 582faed..cb14621 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -686,33 +686,35 @@ static inline void __activate_idle_task(task_t *p, runqueue_t *rq)
 static int recalc_task_prio(task_t *p, unsigned long long now)
 {
 	/* Caller must always ensure 'now >= p->timestamp' */
-	unsigned long long __sleep_time = now - p->timestamp;
-	unsigned long sleep_time;
+	unsigned long sleep_time = now - p->timestamp;
 
 	if (batch_task(p))
 		sleep_time = 0;
-	else {
-		if (__sleep_time > NS_MAX_SLEEP_AVG)
-			sleep_time = NS_MAX_SLEEP_AVG;
-		else
-			sleep_time = (unsigned long)__sleep_time;
-	}
 
 	if (likely(sleep_time > 0)) {
 		/*
-		 * User tasks that sleep a long time are categorised as
-		 * idle. They will only have their sleep_avg increased to a
-		 * level that makes them just interactive priority to stay
-		 * active yet prevent them suddenly becoming cpu hogs and
-		 * starving other processes.
+		 * This ceiling is set to the lowest priority that would allow
+		 * a task to be reinserted into the active array on timeslice
+		 * completion.
 		 */
-		if (p->mm && sleep_time > INTERACTIVE_SLEEP(p)) {
-				unsigned long ceiling;
+		unsigned long ceiling = INTERACTIVE_SLEEP(p);
 
-				ceiling = JIFFIES_TO_NS(MAX_SLEEP_AVG -
-					DEF_TIMESLICE);
-				if (p->sleep_avg < ceiling)
-					p->sleep_avg = ceiling;
+		if (p->mm && sleep_time > ceiling && p->sleep_avg < ceiling) {
+			/*
+			 * Prevents user tasks from achieving best priority
+			 * with one single large enough sleep.
+			 */
+			p->sleep_avg = ceiling;
+			/*
+			 * Using INTERACTIVE_SLEEP() as a ceiling places a
+			 * nice(0) task 1ms sleep away from promotion, and
+			 * gives it 700ms to round-robin with no chance of
+			 * being demoted.  This is more than generous, so
+			 * mark this sleep as non-interactive to prevent the
+			 * on-runqueue bonus logic from intervening should
+			 * this task not receive cpu immediately.
+			 */
+			p->sleep_type = SLEEP_NONINTERACTIVE;
 		} else {
 			/*
 			 * Tasks waking from uninterruptible sleep are
@@ -720,12 +722,12 @@ static int recalc_task_prio(task_t *p, unsigned long long now)
 			 * are likely to be waiting on I/O
 			 */
 			if (p->sleep_type == SLEEP_NONINTERACTIVE && p->mm) {
-				if (p->sleep_avg >= INTERACTIVE_SLEEP(p))
+				if (p->sleep_avg >= ceiling)
 					sleep_time = 0;
 				else if (p->sleep_avg + sleep_time >=
-						INTERACTIVE_SLEEP(p)) {
-					p->sleep_avg = INTERACTIVE_SLEEP(p);
-					sleep_time = 0;
+					 ceiling) {
+						p->sleep_avg = ceiling;
+						sleep_time = 0;
 				}
 			}
 
@@ -739,9 +741,9 @@ static int recalc_task_prio(task_t *p, unsigned long long now)
 			 */
 			p->sleep_avg += sleep_time;
 
-			if (p->sleep_avg > NS_MAX_SLEEP_AVG)
-				p->sleep_avg = NS_MAX_SLEEP_AVG;
 		}
+		if (p->sleep_avg > NS_MAX_SLEEP_AVG)
+			p->sleep_avg = NS_MAX_SLEEP_AVG;
 	}
 
 	return effective_prio(p);