sched: Compute load contribution by a group entity

Unlike task entities who have a fixed weight, group entities instead own a
fraction of their parenting task_group's shares as their contributed weight.

Compute this fraction so that we can correctly account hierarchies and shared
entity nodes.

Signed-off-by: Paul Turner <pjt@google.com>
Reviewed-by: Ben Segall <bsegall@google.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/20120823141506.855074415@google.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

kernel/sched/fair.c

@@ -1117,22 +1117,43 @@ static inline void __update_cfs_rq_tg_load_contrib(struct cfs_rq *cfs_rq,
 		cfs_rq->tg_load_contrib += tg_contrib;
 	}
 }
+
+static inline void __update_group_entity_contrib(struct sched_entity *se)
+{
+	struct cfs_rq *cfs_rq = group_cfs_rq(se);
+	struct task_group *tg = cfs_rq->tg;
+	u64 contrib;
+
+	contrib = cfs_rq->tg_load_contrib * tg->shares;
+	se->avg.load_avg_contrib = div64_u64(contrib,
+					     atomic64_read(&tg->load_avg) + 1);
+}
 #else
 static inline void __update_cfs_rq_tg_load_contrib(struct cfs_rq *cfs_rq,
 						 int force_update) {}
+static inline void __update_group_entity_contrib(struct sched_entity *se) {}
 #endif
 
+static inline void __update_task_entity_contrib(struct sched_entity *se)
+{
+	u32 contrib;
+
+	/* avoid overflowing a 32-bit type w/ SCHED_LOAD_SCALE */
+	contrib = se->avg.runnable_avg_sum * scale_load_down(se->load.weight);
+	contrib /= (se->avg.runnable_avg_period + 1);
+	se->avg.load_avg_contrib = scale_load(contrib);
+}
+
 /* Compute the current contribution to load_avg by se, return any delta */
 static long __update_entity_load_avg_contrib(struct sched_entity *se)
 {
 	long old_contrib = se->avg.load_avg_contrib;
 
-	if (!entity_is_task(se))
-		return 0;
-
-	se->avg.load_avg_contrib = div64_u64(se->avg.runnable_avg_sum *
-					     se->load.weight,
-					     se->avg.runnable_avg_period + 1);
+	if (entity_is_task(se)) {
+		__update_task_entity_contrib(se);
+	} else {
+		__update_group_entity_contrib(se);
+	}
 
 	return se->avg.load_avg_contrib - old_contrib;
 }