[PATCH 05/32] sched: Add sched_class->reweight_task()

Tejun Heo
2023-03-17T21:51:53Z

Currently, during a task weight change, sched core directly calls
reweight_task() defined in fair.c if @p is on CFS. Let's make it a proper
sched_class operation instead. CFS's reweight_task() is renamed to
reweight_task_fair() and now called through sched_class.

While it turns a direct call into an indirect one, set_load_weight() isn't
called from a hot path and this change shouldn't cause any noticeable
difference. This will be used to implement reweight_task for a new BPF
extensible sched_class so that it can keep its cached task weight
up-to-date.

This will be used by a new sched_class to track weight changes.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: David Vernet <dvernet@meta.com>
Acked-by: Josh Don <joshdon@google.com>
Acked-by: Hao Luo <haoluo@google.com>
Acked-by: Barret Rhoden <brho@google.com>
---
kernel/sched/core.c | 4 ++--
kernel/sched/fair.c | 3 ++-
kernel/sched/sched.h | 4 ++--
3 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index fdf4dba12a7e..5a6f4884384e 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1277,8 +1277,8 @@ static void set_load_weight(struct task_struct *p, bool update_load)
* SCHED_OTHER tasks have to update their load when changing their
* weight
*/
- if (update_load && p->sched_class == &fair_sched_class) {
- reweight_task(p, prio);
+ if (update_load && p->sched_class->reweight_task) {
+ p->sched_class->reweight_task(task_rq(p), p, prio);
} else {
load->weight = scale_load(sched_prio_to_weight[prio]);
load->inv_weight = sched_prio_to_wmult[prio];
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 7a1b1f855b96..681ab0dd0bc1 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3342,7 +3342,7 @@ static void reweight_entity(struct cfs_rq *cfs_rq, struct sched_entity *se,

}

-void reweight_task(struct task_struct *p, int prio)
+static void reweight_task_fair(struct rq *rq, struct task_struct *p, int prio)
{
struct sched_entity *se = &p->se;
struct cfs_rq *cfs_rq = cfs_rq_of(se);
@@ -12547,6 +12547,7 @@ DEFINE_SCHED_CLASS(fair) = {
.task_tick = task_tick_fair,
.task_fork = task_fork_fair,

+ .reweight_task = reweight_task_fair,
.prio_changed = prio_changed_fair,
.switched_from = switched_from_fair,
.switched_to = switched_to_fair,
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 3e8df6d31c1e..7934b597053d 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2213,6 +2213,8 @@ struct sched_class {
*/
void (*switched_from)(struct rq *this_rq, struct task_struct *task);
void (*switched_to) (struct rq *this_rq, struct task_struct *task);
+ void (*reweight_task)(struct rq *this_rq, struct task_struct *task,
+ int newprio);
void (*prio_changed) (struct rq *this_rq, struct task_struct *task,
int oldprio);

@@ -2365,8 +2367,6 @@ extern void init_sched_dl_class(void);
extern void init_sched_rt_class(void);
extern void init_sched_fair_class(void);

-extern void reweight_task(struct task_struct *p, int prio);
-
extern void resched_curr(struct rq *rq);
extern void resched_cpu(int cpu);

--
2.39.2