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1/* SPDX-License-Identifier: GPL-2.0 */
2/*
3 * BPF extensible scheduler class: Documentation/scheduler/sched-ext.rst
4 *
5 * Sub-scheduler hierarchy support.
6 *
7 * Copyright (c) 2026 Meta Platforms, Inc. and affiliates.
8 * Copyright (c) 2026 Tejun Heo <[email protected]>
9 */
10#ifndef _KERNEL_SCHED_EXT_SUB_H
11#define _KERNEL_SCHED_EXT_SUB_H
12
13#include "internal.h"
14
15#ifdef CONFIG_EXT_SUB_SCHED
16
17struct scx_sched *scx_skip_subtree_pre(struct scx_sched *pos, struct scx_sched *root);
18struct scx_sched *scx_next_descendant_pre(struct scx_sched *pos, struct scx_sched *root);
19void scx_set_task_sched(struct task_struct *p, struct scx_sched *sch);
20struct cgroup *sch_cgroup(struct scx_sched *sch);
21void set_cgroup_sched(struct cgroup *cgrp, struct scx_sched *sch);
22void scx_pstack_recursion_on_dispatch(struct bpf_prog *prog);
23void scx_pstack_recursion_on_caps_updated(struct bpf_prog *prog);
24void drain_descendants(struct scx_sched *sch);
25void scx_sub_disable(struct scx_sched *sch);
26void scx_sub_enable_workfn(struct kthread_work *work);
27bool scx_bpf_sub_dispatch(u64 cgroup_id, const struct bpf_prog_aux *aux);
28void scx_free_pshards(struct scx_sched *sch);
29s32 scx_alloc_pshards(struct scx_sched *sch);
30void scx_init_root_caps(struct scx_sched *sch);
31void scx_process_sync_ecaps(struct rq *rq, struct task_struct *prev);
32void scx_unbypass_replay_ecaps(struct rq *rq, struct scx_sched *sch);
33void scx_online_ecaps(struct rq *rq);
34void scx_offline_ecaps(struct rq *rq);
35void scx_discard_ecaps_to_sync(s32 cpu, struct scx_sched_pcpu *pcpu);
36void scx_discard_stale_ecaps_syncs(void);
37struct scx_dispatch_q *scx_resolve_local_dsq(struct scx_sched *sch, struct rq *rq,
38 struct task_struct *p, u64 *enq_flags);
39bool scx_task_reenq_on_cap_revoke(struct rq *rq, struct task_struct *p);
40void scx_reenq_reject(struct rq *rq);
41void scx_rescue_charge(struct rq *rq, s64 delta_exec);
42void scx_rescue_end(struct rq *rq);
43bool scx_rescue_keep(struct rq *rq, struct task_struct *p);
44void scx_rescue_flush(struct rq *rq);
45void scx_rescue_dump(struct seq_buf *s, struct rq *rq);
46void scx_rescue_set_knobs(struct scx_sched *sch);
47void scx_rescue_init(struct rq *rq);
48
49/*
50 * cgrp->scx_sched is written by root/sub enable/disable under all of
51 * scx_enable_mutex, scx_fork_rwsem and cgroup_mutex. A new cgroup inherits the
52 * parent's sched under just cgroup_mutex but is not yet reachable by the other
53 * two lock holders. Any one of the three locks stabilizes the association.
54 */
55static inline struct scx_sched *scx_cgroup_sched(struct cgroup *cgrp)
56{
57 return rcu_dereference_check(cgrp->scx_sched,
58 lockdep_is_held(&cgroup_mutex) ||
59 percpu_rwsem_is_held(&scx_fork_rwsem) ||
60 lockdep_is_held(&scx_enable_mutex));
61}
62
63static inline const char *sch_cgrp_path(struct scx_sched *sch)
64{
65 return sch->cgrp_path;
66}
67
68/* a dying sub's hot-path influence ends in scx_sched_free_rcu_work() */
69static inline void scx_dec_has_subs(struct scx_sched *sch)
70{
71 if (sch->level)
72 static_branch_dec(&__scx_has_subs);
73}
74
75#else /* CONFIG_EXT_SUB_SCHED */
76
77static inline struct scx_sched *scx_next_descendant_pre(struct scx_sched *pos, struct scx_sched *root) { return pos ? NULL : root; }
78static inline struct scx_sched *scx_skip_subtree_pre(struct scx_sched *pos, struct scx_sched *root) { return NULL; }
79static inline void scx_set_task_sched(struct task_struct *p, struct scx_sched *sch) {}
80static inline struct cgroup *sch_cgroup(struct scx_sched *sch) { return NULL; }
81static inline const char *sch_cgrp_path(struct scx_sched *sch) { return "/"; }
82static inline void set_cgroup_sched(struct cgroup *cgrp, struct scx_sched *sch) {}
83static inline void drain_descendants(struct scx_sched *sch) { }
84static inline void scx_sub_disable(struct scx_sched *sch) { }
85static inline void scx_free_pshards(struct scx_sched *sch) {}
86static inline s32 scx_alloc_pshards(struct scx_sched *sch) { return 0; }
87static inline void scx_init_root_caps(struct scx_sched *sch) {}
88static inline void scx_process_sync_ecaps(struct rq *rq, struct task_struct *prev) {}
89static inline void scx_unbypass_replay_ecaps(struct rq *rq, struct scx_sched *sch) {}
90static inline void scx_online_ecaps(struct rq *rq) {}
91static inline void scx_offline_ecaps(struct rq *rq) {}
92static inline void scx_discard_ecaps_to_sync(s32 cpu, struct scx_sched_pcpu *pcpu) {}
93static inline void scx_discard_stale_ecaps_syncs(void) {}
94static inline struct scx_dispatch_q *scx_resolve_local_dsq(struct scx_sched *sch, struct rq *rq, struct task_struct *p, u64 *enq_flags) { return &rq->scx.local_dsq; }
95static inline bool scx_task_reenq_on_cap_revoke(struct rq *rq, struct task_struct *p) { return false; }
96static inline void scx_reenq_reject(struct rq *rq) {}
97static inline void scx_rescue_charge(struct rq *rq, s64 delta_exec) {}
98static inline void scx_rescue_end(struct rq *rq) {}
99static inline bool scx_rescue_keep(struct rq *rq, struct task_struct *p) { return false; }
100static inline void scx_rescue_flush(struct rq *rq) {}
101static inline void scx_rescue_dump(struct seq_buf *s, struct rq *rq) {}
102static inline void scx_rescue_set_knobs(struct scx_sched *sch) {}
103static inline void scx_rescue_init(struct rq *rq) {}
104static inline void scx_dec_has_subs(struct scx_sched *sch) {}
105
106#endif /* CONFIG_EXT_SUB_SCHED */
107
108/**
109 * scx_for_each_descendant_pre - pre-order walk of a sched's descendants
110 * @pos: iteration cursor
111 * @root: sched to walk the descendants of
112 *
113 * Walk @root's descendants. @root is included in the iteration and the first
114 * node to be visited. Must be called with scx_enable_mutex, scx_sched_lock, or
115 * RCU read lock.
116 */
117#define scx_for_each_descendant_pre(pos, root) \
118 for ((pos) = scx_next_descendant_pre(NULL, (root)); (pos); \
119 (pos) = scx_next_descendant_pre((pos), (root)))
120
121#ifdef CONFIG_EXT_SUB_SCHED
122
123/**
124 * scx_missing_caps - The caps in @needed that @sch lacks on @cpu
125 * @sch: sched to test
126 * @cpu: cpu to test on
127 * @needed: bitmask of SCX_CAP_* values
128 *
129 * Return the caps in @needed that @sch lacks for @cpu, 0 if it holds them all.
130 */
131static inline u64 scx_missing_caps(struct scx_sched *sch, s32 cpu, u64 needed)
132{
133 u64 ecaps;
134
135 /* no sub-scheds, no missing caps */
136 if (!scx_has_subs())
137 return 0;
138
139 /* root holds every cap on every cpu */
140 if (!sch->level)
141 return 0;
142
143 ecaps = READ_ONCE(per_cpu_ptr(sch->pcpu, cpu)->ecaps);
144
145 return needed & ~ecaps;
146}
147
148/*
149 * Cap semantics: which caps an action requires, and which caps a cap implies.
150 * Keep all such mappings collected here.
151 */
152
153/* map @enq_flags to the SCX_CAP_* bit required for the local-DSQ insert */
154static inline u64 scx_caps_for_enq(u64 enq_flags)
155{
156 /* a restored task must be put into the local DSQ regardless of caps */
157 if (unlikely(enq_flags & SCX_ENQ_IGNORE_CAPS))
158 return 0;
159 if (enq_flags & SCX_ENQ_IMMED)
160 return SCX_CAP_ENQ_IMMED;
161 return SCX_CAP_ENQ;
162}
163
164/* map queued @p to the SCX_CAP_* bit required to stay on its local DSQ */
165static inline u64 scx_caps_for_task(struct task_struct *p)
166{
167 if (p->scx.flags & SCX_TASK_IMMED)
168 return SCX_CAP_ENQ_IMMED;
169 return SCX_CAP_ENQ;
170}
171
172/* the cap @sch needs to preempt @rq's current task, 0 if none */
173static inline u64 scx_caps_for_preempt(struct scx_sched *sch, struct rq *rq, u64 enq_flags)
174{
175 struct task_struct *curr = rq->curr;
176
177 /* a kernel-forced placement preempts regardless of caps */
178 if (unlikely(enq_flags & SCX_ENQ_IGNORE_CAPS))
179 return 0;
180 /* a non-ext task can't be preempted by ext, own-subtree needs no cap */
181 if (curr->sched_class != &ext_sched_class ||
182 scx_is_descendant(scx_task_sched(curr), sch))
183 return 0;
184 return SCX_CAP_PREEMPT;
185}
186
187/* caps implied by holding @cap */
188static inline u64 scx_caps_implied(u64 cap)
189{
190 switch (cap) {
191 case SCX_CAP_PREEMPT:
192 return SCX_CAP_ENQ | SCX_CAP_ENQ_IMMED;
193 case SCX_CAP_ENQ:
194 return SCX_CAP_ENQ_IMMED;
195 }
196 return 0;
197}
198
199/* may @p keep running on @rq's cpu? requires baseline cpu access */
200static inline bool scx_task_can_stay_on_cpu(struct rq *rq, struct task_struct *p)
201{
202 if (!scx_has_subs())
203 return true;
204
205 /* a migration-disabled task is let in without caps, keep it likewise */
206 if (unlikely(is_migration_disabled(p)))
207 return true;
208
209 return likely(!scx_missing_caps(scx_task_sched(p), cpu_of(rq), SCX_CAP_BASE));
210}
211
212/* the task admitted for rescue on @rq, NULL if none */
213static inline struct task_struct *scx_rescuee(struct rq *rq)
214{
215 lockdep_assert_rq_held(rq);
216
217 if (!scx_has_subs())
218 return NULL;
219
220 return rq->scx.rescue.curr;
221}
222
223#else /* CONFIG_EXT_SUB_SCHED */
224
225static inline u64 scx_missing_caps(struct scx_sched *sch, s32 cpu, u64 needed) { return 0; }
226static inline u64 scx_caps_for_preempt(struct scx_sched *sch, struct rq *rq, u64 enq_flags) { return 0; }
227static inline bool scx_task_can_stay_on_cpu(struct rq *rq, struct task_struct *p) { return true; }
228static inline struct task_struct *scx_rescuee(struct rq *rq) { return NULL; }
229
230#endif /* CONFIG_EXT_SUB_SCHED */
231
232#endif /* _KERNEL_SCHED_EXT_SUB_H */