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Message-Id: <20230128001639.3510083-7-tj@kernel.org> Date: Fri, 27 Jan 2023 14:16:15 -1000 From: Tejun Heo <tj@...nel.org> To: torvalds@...ux-foundation.org, mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com, vincent.guittot@...aro.org, dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de, bristot@...hat.com, vschneid@...hat.com, ast@...nel.org, daniel@...earbox.net, andrii@...nel.org, martin.lau@...nel.org, joshdon@...gle.com, brho@...gle.com, pjt@...gle.com, derkling@...gle.com, haoluo@...gle.com, dvernet@...a.com, dschatzberg@...a.com, dskarlat@...cmu.edu, riel@...riel.com Cc: linux-kernel@...r.kernel.org, bpf@...r.kernel.org, kernel-team@...a.com, Tejun Heo <tj@...nel.org> Subject: [PATCH 06/30] sched: Add sched_class->switching_to() and expose check_class_changing/changed() When a task switches to a new sched_class, the prev and new classes are notified through ->switched_from() and ->switched_to(), respectively, after the switching is done. A new BPF extensible sched_class will have callbacks that allow the BPF scheduler to keep track of relevant task states (like priority and cpumask). Those callbacks aren't called while a task is on a different sched_class. When a task comes back, we wanna tell the BPF progs the up-to-date state before the task gets enqueued, so we need a hook which is called before the switching is committed. This patch adds ->switching_to() which is called during sched_class switch through check_class_changing() before the task is restored. Also, this patch exposes check_class_changing/changed() in kernel/sched/sched.h. They will be used by the new BPF extensible sched_class to implement implicit sched_class switching which is used e.g. when falling back to CFS when the BPF scheduler fails or unloads. This is a prep patch and doesn't cause any behavior changes. The new operation and exposed functions aren't used yet. v2: Improve patch description w/ details on planned use. Signed-off-by: Tejun Heo <tj@...nel.org> Reviewed-by: David Vernet <dvernet@...a.com> Acked-by: Josh Don <joshdon@...gle.com> Acked-by: Hao Luo <haoluo@...gle.com> Acked-by: Barret Rhoden <brho@...gle.com> --- kernel/sched/core.c | 20 +++++++++++++++++--- kernel/sched/sched.h | 7 +++++++ 2 files changed, 24 insertions(+), 3 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index ce27ed857975..e6d5374edf58 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -2221,6 +2221,17 @@ inline int task_curr(const struct task_struct *p) return cpu_curr(task_cpu(p)) == p; } +/* + * ->switching_to() is called with the pi_lock and rq_lock held and must not + * mess with locking. + */ +void check_class_changing(struct rq *rq, struct task_struct *p, + const struct sched_class *prev_class) +{ + if (prev_class != p->sched_class && p->sched_class->switching_to) + p->sched_class->switching_to(rq, p); +} + /* * switched_from, switched_to and prio_changed must _NOT_ drop rq->lock, * use the balance_callback list if you want balancing. @@ -2228,9 +2239,9 @@ inline int task_curr(const struct task_struct *p) * this means any call to check_class_changed() must be followed by a call to * balance_callback(). */ -static inline void check_class_changed(struct rq *rq, struct task_struct *p, - const struct sched_class *prev_class, - int oldprio) +void check_class_changed(struct rq *rq, struct task_struct *p, + const struct sched_class *prev_class, + int oldprio) { if (prev_class != p->sched_class) { if (prev_class->switched_from) @@ -7072,6 +7083,7 @@ void rt_mutex_setprio(struct task_struct *p, struct task_struct *pi_task) } __setscheduler_prio(p, prio); + check_class_changing(rq, p, prev_class); } check_class_changed(rq, p, prev_class, oldprio); @@ -7681,6 +7693,8 @@ static int __sched_setscheduler(struct task_struct *p, } __setscheduler_uclamp(p, attr); + check_class_changing(rq, p, prev_class); + /* * We enqueue to tail when the priority of a task is * increased (user space view). diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index 070603f00470..c083395c5477 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -2206,6 +2206,7 @@ struct sched_class { * cannot assume the switched_from/switched_to pair is serialized by * rq->lock. They are however serialized by p->pi_lock. */ + void (*switching_to) (struct rq *this_rq, struct task_struct *task); 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, @@ -2442,6 +2443,12 @@ static inline void sub_nr_running(struct rq *rq, unsigned count) extern void activate_task(struct rq *rq, struct task_struct *p, int flags); extern void deactivate_task(struct rq *rq, struct task_struct *p, int flags); +extern void check_class_changing(struct rq *rq, struct task_struct *p, + const struct sched_class *prev_class); +extern void check_class_changed(struct rq *rq, struct task_struct *p, + const struct sched_class *prev_class, + int oldprio); + extern void check_preempt_curr(struct rq *rq, struct task_struct *p, int flags); #ifdef CONFIG_PREEMPT_RT -- 2.39.1
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