1 files changed, 27 insertions, 25 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index 582faed3d360..cb146219d532 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);