1 files changed, 129 insertions, 0 deletions

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 6b800a14b990..16d67f9b6955 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -971,6 +971,126 @@ static inline void update_entity_shares_tick(struct cfs_rq *cfs_rq)
 }
 #endif /* CONFIG_FAIR_GROUP_SCHED */
 
+#ifdef CONFIG_SMP
+/*
+ * Approximate:
+ *   val * y^n,    where y^32 ~= 0.5 (~1 scheduling period)
+ */
+static __always_inline u64 decay_load(u64 val, u64 n)
+{
+        for (; n && val; n--) {
+                val *= 4008;
+                val >>= 12;
+        }
+
+        return val;
+}
+
+/*
+ * We can represent the historical contribution to runnable average as the
+ * coefficients of a geometric series.  To do this we sub-divide our runnable
+ * history into segments of approximately 1ms (1024us); label the segment that
+ * occurred N-ms ago p_N, with p_0 corresponding to the current period, e.g.
+ *
+ * [<- 1024us ->|<- 1024us ->|<- 1024us ->| ...
+ *      p0            p1           p2
+ *     (now)       (~1ms ago)  (~2ms ago)
+ *
+ * Let u_i denote the fraction of p_i that the entity was runnable.
+ *
+ * We then designate the fractions u_i as our co-efficients, yielding the
+ * following representation of historical load:
+ *   u_0 + u_1*y + u_2*y^2 + u_3*y^3 + ...
+ *
+ * We choose y based on the with of a reasonably scheduling period, fixing:
+ *   y^32 = 0.5
+ *
+ * This means that the contribution to load ~32ms ago (u_32) will be weighted
+ * approximately half as much as the contribution to load within the last ms
+ * (u_0).
+ *
+ * When a period "rolls over" and we have new u_0`, multiplying the previous
+ * sum again by y is sufficient to update:
+ *   load_avg = u_0` + y*(u_0 + u_1*y + u_2*y^2 + ... )
+ *            = u_0 + u_1*y + u_2*y^2 + ... [re-labeling u_i --> u_{i+1}]
+ */
+static __always_inline int __update_entity_runnable_avg(u64 now,
+                                                        struct sched_avg *sa,
+                                                        int runnable)
+{
+        u64 delta;
+        int delta_w, decayed = 0;
+
+        delta = now - sa->last_runnable_update;
+        /*
+         * This should only happen when time goes backwards, which it
+         * unfortunately does during sched clock init when we swap over to TSC.
+         */
+        if ((s64)delta < 0) {
+                sa->last_runnable_update = now;
+                return 0;
+        }
+
+        /*
+         * Use 1024ns as the unit of measurement since it's a reasonable
+         * approximation of 1us and fast to compute.
+         */
+        delta >>= 10;
+        if (!delta)
+                return 0;
+        sa->last_runnable_update = now;
+
+        /* delta_w is the amount already accumulated against our next period */
+        delta_w = sa->runnable_avg_period % 1024;
+        if (delta + delta_w >= 1024) {
+                /* period roll-over */
+                decayed = 1;
+
+                /*
+                 * Now that we know we're crossing a period boundary, figure
+                 * out how much from delta we need to complete the current
+                 * period and accrue it.
+                 */
+                delta_w = 1024 - delta_w;
+                BUG_ON(delta_w > delta);
+                do {
+                        if (runnable)
+                                sa->runnable_avg_sum += delta_w;
+                        sa->runnable_avg_period += delta_w;
+
+                        /*
+                         * Remainder of delta initiates a new period, roll over
+                         * the previous.
+                         */
+                        sa->runnable_avg_sum =
+                                decay_load(sa->runnable_avg_sum, 1);
+                        sa->runnable_avg_period =
+                                decay_load(sa->runnable_avg_period, 1);
+
+                        delta -= delta_w;
+                        /* New period is empty */
+                        delta_w = 1024;
+                } while (delta >= 1024);
+        }
+
+        /* Remainder of delta accrued against u_0` */
+        if (runnable)
+                sa->runnable_avg_sum += delta;
+        sa->runnable_avg_period += delta;
+
+        return decayed;
+}
+
+/* Update a sched_entity's runnable average */
+static inline void update_entity_load_avg(struct sched_entity *se)
+{
+        __update_entity_runnable_avg(rq_of(cfs_rq_of(se))->clock_task, &se->avg,
+                                     se->on_rq);
+}
+#else
+static inline void update_entity_load_avg(struct sched_entity *se) {}
+#endif
+
 static void enqueue_sleeper(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
 #ifdef CONFIG_SCHEDSTATS
@@ -1097,6 +1217,7 @@ enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
          */
         update_curr(cfs_rq);
         update_cfs_load(cfs_rq, 0);
+        update_entity_load_avg(se);
         account_entity_enqueue(cfs_rq, se);
         update_cfs_shares(cfs_rq);
 
@@ -1171,6 +1292,7 @@ dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
          * Update run-time statistics of the 'current'.
          */
         update_curr(cfs_rq);
+        update_entity_load_avg(se);
 
         update_stats_dequeue(cfs_rq, se);
         if (flags & DEQUEUE_SLEEP) {
@@ -1340,6 +1462,8 @@ static void put_prev_entity(struct cfs_rq *cfs_rq, struct sched_entity *prev)
                 update_stats_wait_start(cfs_rq, prev);
                 /* Put 'current' back into the tree. */
                 __enqueue_entity(cfs_rq, prev);
+                /* in !on_rq case, update occurred at dequeue */
+                update_entity_load_avg(prev);
         }
         cfs_rq->curr = NULL;
 }
@@ -1353,6 +1477,11 @@ entity_tick(struct cfs_rq *cfs_rq, struct sched_entity *curr, int queued)
         update_curr(cfs_rq);
 
         /*
+         * Ensure that runnable average is periodically updated.
+         */
+        update_entity_load_avg(curr);
+
+        /*
          * Update share accounting for long-running entities.
          */
         update_entity_shares_tick(cfs_rq);