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

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

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index f79951facff4ebc09a91580e5ac8475c50c1351e..65b1065f9b21c09f6f2ad7cec0e2c6b739dafcc7 100644 (file)
--- a/kernel/sched/fair.c
+++ b/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);
@@ -5131,7 +5131,7 @@ 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);
 

diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 82522c98c903e313cfbeec2a7bbeef03053a9a0b..3334aa53542367d311c6b126eedb0959b0336081 100644 (file)
--- a/kernel/sched/sched.h
+++ b/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