[PATCH 04/39] sched: Add sched_class->reweight_task()

[Tejun Heo]

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.

Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Reviewed-by: David Vernet <dvernet@xxxxxxxx>
Acked-by: Josh Don <joshdon@xxxxxxxxxx>
Acked-by: Hao Luo <haoluo@xxxxxxxxxx>
Acked-by: Barret Rhoden <brho@xxxxxxxxxx>
---
 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 b12b1b7405fd..4b9cb2228b04 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1342,8 +1342,8 @@ 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 03be0d1330a6..5d7cffee1a4e 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3835,7 +3835,7 @@ 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);
@@ -13135,6 +13135,7 @@ 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 d2242679239e..8e23f19e8096 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2303,6 +2303,8 @@ 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);
 
@@ -2460,8 +2462,6 @@ 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);
 
-- 
2.44.0