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

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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
This commit is contained in:
Ingo Molnar
2025-11-26 12:09:16 +01:00
parent 80390ead20
commit 4ff674fa98
2 changed files with 9 additions and 9 deletions
Download Patch File Download Diff File Expand all files Collapse all files

16
kernel/sched/fair.c
View File

@@ -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);

2
kernel/sched/sched.h
View File

@@ -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