sched/fair: Rename cfs_rq::avg_load to cfs_rq::sum_weight

[ Upstream commit 4ff674f ]

The ::avg_load field is a long-standing misnomer: it says it's an
'average load', but in reality it's the momentary sum of the load
of all currently runnable tasks. We'd have to also perform a
division by nr_running (or use time-decay) to arrive at any sort
of average value.

This is clear from comments about the math of fair scheduling:

    *              \Sum w_i := cfs_rq->avg_load

The sum of all weights is ... the sum of all weights, not
the average of all weights.

To make it doubly confusing, there's also an ::avg_load
in the load-balancing struct sg_lb_stats, which *is* a
true average.

The second part of the field's name is a minor misnomer
as well: it says 'load', and it is indeed a load_weight
structure as it shares code with the load-balancer - but
it's only in an SMP load-balancing context where
load = weight, in the fair scheduling context the primary
purpose is the weighting of different nice levels.

So rename the field to ::sum_weight instead, which makes
the terminology of the EEVDF math match up with our
implementation of it:

    *              \Sum w_i := cfs_rq->sum_weight

Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://patch.msgid.link/20251201064647.1851919-6-mingo@kernel.org
Stable-dep-of: b3d99f4 ("sched/fair: Fix zero_vruntime tracking")
Signed-off-by: Sasha Levin <sashal@kernel.org>

Author: ingomolnar

kernel/sched/fair.c

@@ -608,7 +608,7 @@ static inline s64 entity_key(struct cfs_rq *cfs_rq, struct sched_entity *se)
  *
  *                    v0 := cfs_rq->zero_vruntime
  * \Sum (v_i - v0) * w_i := cfs_rq->avg_vruntime
- *              \Sum w_i := cfs_rq->avg_load
+ *              \Sum w_i := cfs_rq->sum_weight
  *
  * Since zero_vruntime closely tracks the per-task service, these
  * deltas: (v_i - v), will be in the order of the maximal (virtual) lag
@@ -625,7 +625,7 @@ avg_vruntime_add(struct cfs_rq *cfs_rq, struct sched_entity *se)
 	s64 key = entity_key(cfs_rq, se);
 
 	cfs_rq->avg_vruntime += key * weight;
-	cfs_rq->avg_load += weight;
+	cfs_rq->sum_weight += weight;
 }
 
 static void
@@ -635,16 +635,16 @@ avg_vruntime_sub(struct cfs_rq *cfs_rq, struct sched_entity *se)
 	s64 key = entity_key(cfs_rq, se);
 
 	cfs_rq->avg_vruntime -= key * weight;
-	cfs_rq->avg_load -= weight;
+	cfs_rq->sum_weight -= weight;
 }
 
 static inline
 void avg_vruntime_update(struct cfs_rq *cfs_rq, s64 delta)
 {
 	/*
-	 * v' = v + d ==> avg_vruntime' = avg_runtime - d*avg_load
+	 * v' = v + d ==> avg_vruntime' = avg_runtime - d*sum_weight
 	 */
-	cfs_rq->avg_vruntime -= cfs_rq->avg_load * delta;
+	cfs_rq->avg_vruntime -= cfs_rq->sum_weight * delta;
 }
 
 /*
@@ -655,7 +655,7 @@ u64 avg_vruntime(struct cfs_rq *cfs_rq)
 {
 	struct sched_entity *curr = cfs_rq->curr;
 	s64 avg = cfs_rq->avg_vruntime;
-	long load = cfs_rq->avg_load;
+	long load = cfs_rq->sum_weight;
 
 	if (curr && curr->on_rq) {
 		unsigned long weight = scale_load_down(curr->load.weight);
@@ -723,7 +723,7 @@ static int vruntime_eligible(struct cfs_rq *cfs_rq, u64 vruntime)
 {
 	struct sched_entity *curr = cfs_rq->curr;
 	s64 avg = cfs_rq->avg_vruntime;
-	long load = cfs_rq->avg_load;
+	long load = cfs_rq->sum_weight;
 
 	if (curr && curr->on_rq) {
 		unsigned long weight = scale_load_down(curr->load.weight);
@@ -5175,7 +5175,7 @@ place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
 		 *
 		 *   vl_i = (W + w_i)*vl'_i / W
 		 */
-		load = cfs_rq->avg_load;
+		load = cfs_rq->sum_weight;
 		if (curr && curr->on_rq)
 			load += scale_load_down(curr->load.weight);
 

kernel/sched/sched.h

@@ -679,7 +679,7 @@ struct cfs_rq {
 	unsigned int		h_nr_idle; /* SCHED_IDLE */
 
 	s64			avg_vruntime;
-	u64			avg_load;
+	u64			sum_weight;
 
 	u64			zero_vruntime;
 #ifdef CONFIG_SCHED_CORE