[RFC][PATCH 06/14] sched/fair: Move enqueue migrate handling

[Peter Zijlstra]

Move the entity migrate handling from enqueue_entity_load_avg() to
update_load_avg(). This has two benefits:

 - {en,de}queue_entity_load_avg() will become purely about managing
   runnable_load

 - we can avoid a double update_tg_load_avg() and reduce pressure on
   the global tg->shares cacheline

The reason we do this is so that we can change update_cfs_shares() to
change both weight and (future) runnable_weight. For this to work we
need to have the cfs_rq averages up-to-date (which means having done
the attach), but we need the cfs_rq->avg.runnable_avg to not yet
include the se's contribution (since se->on_rq == 0).

Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
 kernel/sched/fair.c |   70 ++++++++++++++++++++++++++--------------------------
 1 file changed, 36 insertions(+), 34 deletions(-)

--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3418,34 +3418,6 @@ update_cfs_rq_load_avg(u64 now, struct c
 	return decayed || removed_load;
 }
 
-/*
- * Optional action to be done while updating the load average
- */
-#define UPDATE_TG	0x1
-#define SKIP_AGE_LOAD	0x2
-
-/* Update task and its cfs_rq load average */
-static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
-{
-	u64 now = cfs_rq_clock_task(cfs_rq);
-	struct rq *rq = rq_of(cfs_rq);
-	int cpu = cpu_of(rq);
-	int decayed;
-
-	/*
-	 * Track task load average for carrying it to new CPU after migrated, and
-	 * track group sched_entity load average for task_h_load calc in migration
-	 */
-	if (se->avg.last_update_time && !(flags & SKIP_AGE_LOAD))
-		__update_load_avg_se(now, cpu, cfs_rq, se);
-
-	decayed  = update_cfs_rq_load_avg(now, cfs_rq, true);
-	decayed |= propagate_entity_load_avg(se);
-
-	if (decayed && (flags & UPDATE_TG))
-		update_tg_load_avg(cfs_rq, 0);
-}
-
 /**
  * attach_entity_load_avg - attach this entity to its cfs_rq load avg
  * @cfs_rq: cfs_rq to attach to
@@ -3486,17 +3458,46 @@ static void detach_entity_load_avg(struc
 	cfs_rq_util_change(cfs_rq);
 }
 
+/*
+ * Optional action to be done while updating the load average
+ */
+#define UPDATE_TG	0x1
+#define SKIP_AGE_LOAD	0x2
+#define DO_ATTACH	0x4
+
+/* Update task and its cfs_rq load average */
+static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
+{
+	u64 now = cfs_rq_clock_task(cfs_rq);
+	struct rq *rq = rq_of(cfs_rq);
+	int cpu = cpu_of(rq);
+	int decayed;
+
+	/*
+	 * Track task load average for carrying it to new CPU after migrated, and
+	 * track group sched_entity load average for task_h_load calc in migration
+	 */
+	if (se->avg.last_update_time && !(flags & SKIP_AGE_LOAD))
+		__update_load_avg_se(now, cpu, cfs_rq, se);
+
+	decayed  = update_cfs_rq_load_avg(now, cfs_rq, true);
+	decayed |= propagate_entity_load_avg(se);
+
+	if (!se->avg.last_update_time && (flags & DO_ATTACH)) {
+
+		attach_entity_load_avg(cfs_rq, se);
+		update_tg_load_avg(cfs_rq, 0);
+
+	} else if (decayed && (flags & UPDATE_TG))
+		update_tg_load_avg(cfs_rq, 0);
+}
+
 /* Add the load generated by se into cfs_rq's load average */
 static inline void
 enqueue_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
 	cfs_rq->runnable_load_avg += se->avg.load_avg;
 	cfs_rq->runnable_load_sum += se_weight(se) * se->avg.load_sum;
-
-	if (!se->avg.last_update_time) {
-		attach_entity_load_avg(cfs_rq, se);
-		update_tg_load_avg(cfs_rq, 0);
-	}
 }
 
 /* Remove the runnable load generated by se from cfs_rq's runnable load average */
@@ -3586,6 +3587,7 @@ update_cfs_rq_load_avg(u64 now, struct c
 
 #define UPDATE_TG	0x0
 #define SKIP_AGE_LOAD	0x0
+#define DO_ATTACH	0x0
 
 static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se, int not_used1)
 {
@@ -3740,7 +3742,7 @@ enqueue_entity(struct cfs_rq *cfs_rq, st
 	 *     its group cfs_rq
 	 *   - Add its new weight to cfs_rq->load.weight
 	 */
-	update_load_avg(cfs_rq, se, UPDATE_TG);
+	update_load_avg(cfs_rq, se, UPDATE_TG | DO_ATTACH);
 	enqueue_entity_load_avg(cfs_rq, se);
 	update_cfs_shares(se);
 	account_entity_enqueue(cfs_rq, se);