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Message-ID: <20251201064647.1851919-7-mingo@kernel.org>
Date: Mon, 1 Dec 2025 07:46:47 +0100
From: Ingo Molnar <mingo@...nel.org>
To: linux-kernel@...r.kernel.org
Cc: Peter Zijlstra <peterz@...radead.org>,
Juri Lelli <juri.lelli@...hat.com>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Valentin Schneider <vschneid@...hat.com>,
Vincent Guittot <vincent.guittot@...aro.org>,
Shrikanth Hegde <sshegde@...ux.ibm.com>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Mel Gorman <mgorman@...e.de>,
Steven Rostedt <rostedt@...dmis.org>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...nel.org>
Subject: [PATCH 6/6] sched/fair: Rename cfs_rq::avg_vruntime to ::sum_w_vruntime, and helper functions
The ::avg_vruntime field is a misnomer: it says it's an
'average vruntime', but in reality it's the momentary sum
of the weighted vruntimes of all queued tasks, which is
at least a division away from being an average.
This is clear from comments about the math of fair scheduling:
* \Sum (v_i - v0) * w_i := cfs_rq->avg_vruntime
This confusion is increased by the cfs_avg_vruntime() function,
which does perform the division and returns a true average.
The sum of all weighted vruntimes should be named thusly,
so rename the field to ::sum_w_vruntime. (As arguably
::sum_weighted_vruntime would be a bit of a mouthful.)
Understanding the scheduler is hard enough already, without
extra layers of obfuscated naming. ;-)
Also rename related helper functions:
sum_vruntime_add() => sum_w_vruntime_add()
sum_vruntime_sub() => sum_w_vruntime_sub()
sum_vruntime_update() => sum_w_vruntime_update()
With the notable exception of cfs_avg_vruntime(), which
was named accurately.
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
kernel/sched/debug.c | 2 +-
kernel/sched/fair.c | 26 +++++++++++++-------------
kernel/sched/sched.h | 2 +-
3 files changed, 15 insertions(+), 15 deletions(-)
diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index a6ceda12bd35..b6fa5ca6a932 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -828,7 +828,7 @@ void print_cfs_rq(struct seq_file *m, int cpu, struct cfs_rq *cfs_rq)
SPLIT_NS(left_vruntime));
SEQ_printf(m, " .%-30s: %Ld.%06ld\n", "zero_vruntime",
SPLIT_NS(zero_vruntime));
- SEQ_printf(m, " .%-30s: %Ld.%06ld\n", "avg_vruntime",
+ SEQ_printf(m, " .%-30s: %Ld.%06ld\n", "sum_w_vruntime",
SPLIT_NS(cfs_avg_vruntime(cfs_rq)));
SEQ_printf(m, " .%-30s: %Ld.%06ld\n", "right_vruntime",
SPLIT_NS(right_vruntime));
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 2ffd52a2e7a0..41ede30b74cd 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -607,7 +607,7 @@ static inline s64 entity_key(struct cfs_rq *cfs_rq, struct sched_entity *se)
* Which we track using:
*
* v0 := cfs_rq->zero_vruntime
- * \Sum (v_i - v0) * w_i := cfs_rq->avg_vruntime
+ * \Sum (v_i - v0) * w_i := cfs_rq->sum_w_vruntime
* \Sum w_i := cfs_rq->sum_weight
*
* Since zero_vruntime closely tracks the per-task service, these
@@ -619,32 +619,32 @@ static inline s64 entity_key(struct cfs_rq *cfs_rq, struct sched_entity *se)
* As measured, the max (key * weight) value was ~44 bits for a kernel build.
*/
static void
-avg_vruntime_add(struct cfs_rq *cfs_rq, struct sched_entity *se)
+sum_w_vruntime_add(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
unsigned long weight = scale_load_down(se->load.weight);
s64 key = entity_key(cfs_rq, se);
- cfs_rq->avg_vruntime += key * weight;
+ cfs_rq->sum_w_vruntime += key * weight;
cfs_rq->sum_weight += weight;
}
static void
-avg_vruntime_sub(struct cfs_rq *cfs_rq, struct sched_entity *se)
+sum_w_vruntime_sub(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
unsigned long weight = scale_load_down(se->load.weight);
s64 key = entity_key(cfs_rq, se);
- cfs_rq->avg_vruntime -= key * weight;
+ cfs_rq->sum_w_vruntime -= key * weight;
cfs_rq->sum_weight -= weight;
}
static inline
-void avg_vruntime_update(struct cfs_rq *cfs_rq, s64 delta)
+void sum_w_vruntime_update(struct cfs_rq *cfs_rq, s64 delta)
{
/*
- * v' = v + d ==> avg_vruntime' = avg_runtime - d*sum_weight
+ * v' = v + d ==> sum_w_vruntime' = sum_runtime - d*sum_weight
*/
- cfs_rq->avg_vruntime -= cfs_rq->sum_weight * delta;
+ cfs_rq->sum_w_vruntime -= cfs_rq->sum_weight * delta;
}
/*
@@ -654,7 +654,7 @@ void avg_vruntime_update(struct cfs_rq *cfs_rq, s64 delta)
u64 cfs_avg_vruntime(struct cfs_rq *cfs_rq)
{
struct sched_entity *curr = cfs_rq->curr;
- s64 avg = cfs_rq->avg_vruntime;
+ s64 avg = cfs_rq->sum_w_vruntime;
long load = cfs_rq->sum_weight;
if (curr && curr->on_rq) {
@@ -722,7 +722,7 @@ static void update_entity_lag(struct cfs_rq *cfs_rq, struct sched_entity *se)
static int vruntime_eligible(struct cfs_rq *cfs_rq, u64 vruntime)
{
struct sched_entity *curr = cfs_rq->curr;
- s64 avg = cfs_rq->avg_vruntime;
+ s64 avg = cfs_rq->sum_w_vruntime;
long load = cfs_rq->sum_weight;
if (curr && curr->on_rq) {
@@ -745,7 +745,7 @@ static void update_zero_vruntime(struct cfs_rq *cfs_rq)
u64 vruntime = cfs_avg_vruntime(cfs_rq);
s64 delta = (s64)(vruntime - cfs_rq->zero_vruntime);
- avg_vruntime_update(cfs_rq, delta);
+ sum_w_vruntime_update(cfs_rq, delta);
cfs_rq->zero_vruntime = vruntime;
}
@@ -819,7 +819,7 @@ RB_DECLARE_CALLBACKS(static, min_vruntime_cb, struct sched_entity,
*/
static void __enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
- avg_vruntime_add(cfs_rq, se);
+ sum_w_vruntime_add(cfs_rq, se);
update_zero_vruntime(cfs_rq);
se->min_vruntime = se->vruntime;
se->min_slice = se->slice;
@@ -831,7 +831,7 @@ static void __dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
rb_erase_augmented_cached(&se->run_node, &cfs_rq->tasks_timeline,
&min_vruntime_cb);
- avg_vruntime_sub(cfs_rq, se);
+ sum_w_vruntime_sub(cfs_rq, se);
update_zero_vruntime(cfs_rq);
}
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 54994d93958a..f0eb58458ff3 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -678,7 +678,7 @@ struct cfs_rq {
unsigned int h_nr_runnable; /* SCHED_{NORMAL,BATCH,IDLE} */
unsigned int h_nr_idle; /* SCHED_IDLE */
- s64 avg_vruntime;
+ s64 sum_w_vruntime;
u64 sum_weight;
u64 zero_vruntime;
--
2.51.0
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