Commit e83edbf8 authored Jun 18, 2024 by Tejun Heo

sched: Add sched_class->reweight_task()



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@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>

parent 304b3f2b

kernel/sched/core.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -1343,8 +1343,8 @@ 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];

kernel/sched/fair.c

+2 −1

Original line number	Diff line number	Diff line
		@@ -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);
		@@ -13221,6 +13221,7 @@ 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,

kernel/sched/sched.h

+2 −2

Original line number	Diff line number	Diff line
		@@ -2324,6 +2324,8 @@ 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);

		@@ -2509,8 +2511,6 @@ 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);