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 <tj@kernel.org> 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 17 struct scx_sched *scx_skip_subtree_pre(struct scx_sched *pos, struct scx_sched *root); 18 struct scx_sched *scx_next_descendant_pre(struct scx_sched *pos, struct scx_sched *root); 19 void scx_set_task_sched(struct task_struct *p, struct scx_sched *sch); 20 struct cgroup *sch_cgroup(struct scx_sched *sch); 21 void set_cgroup_sched(struct cgroup *cgrp, struct scx_sched *sch); 22 void scx_pstack_recursion_on_dispatch(struct bpf_prog *prog); 23 void scx_pstack_recursion_on_caps_updated(struct bpf_prog *prog); 24 void drain_descendants(struct scx_sched *sch); 25 void scx_sub_disable(struct scx_sched *sch); 26 void scx_sub_enable_workfn(struct kthread_work *work); 27 bool scx_bpf_sub_dispatch(u64 cgroup_id, const struct bpf_prog_aux *aux); 28 void scx_free_pshards(struct scx_sched *sch); 29 s32 scx_alloc_pshards(struct scx_sched *sch); 30 void scx_init_root_caps(struct scx_sched *sch); 31 void scx_process_sync_ecaps(struct rq *rq, struct task_struct *prev); 32 void scx_unbypass_replay_ecaps(struct rq *rq, struct scx_sched *sch); 33 void scx_online_ecaps(struct rq *rq); 34 void scx_offline_ecaps(struct rq *rq); 35 void scx_discard_ecaps_to_sync(s32 cpu, struct scx_sched_pcpu *pcpu); 36 void scx_discard_stale_ecaps_syncs(void); 37 struct scx_dispatch_q *scx_resolve_local_dsq(struct scx_sched *sch, struct rq *rq, 38 struct task_struct *p, u64 *enq_flags); 39 bool scx_task_reenq_on_cap_revoke(struct rq *rq, struct task_struct *p); 40 void scx_reenq_reject(struct rq *rq); 41 void scx_rescue_charge(struct rq *rq, s64 delta_exec); 42 void scx_rescue_end(struct rq *rq); 43 bool scx_rescue_keep(struct rq *rq, struct task_struct *p); 44 void scx_rescue_flush(struct rq *rq); 45 void scx_rescue_dump(struct seq_buf *s, struct rq *rq); 46 void scx_rescue_set_knobs(struct scx_sched *sch); 47 void 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 */ 55 static 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 63 static 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() */ 69 static 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 77 static inline struct scx_sched *scx_next_descendant_pre(struct scx_sched *pos, struct scx_sched *root) { return pos ? NULL : root; } 78 static inline struct scx_sched *scx_skip_subtree_pre(struct scx_sched *pos, struct scx_sched *root) { return NULL; } 79 static inline void scx_set_task_sched(struct task_struct *p, struct scx_sched *sch) {} 80 static inline struct cgroup *sch_cgroup(struct scx_sched *sch) { return NULL; } 81 static inline const char *sch_cgrp_path(struct scx_sched *sch) { return "/"; } 82 static inline void set_cgroup_sched(struct cgroup *cgrp, struct scx_sched *sch) {} 83 static inline void drain_descendants(struct scx_sched *sch) { } 84 static inline void scx_sub_disable(struct scx_sched *sch) { } 85 static inline void scx_free_pshards(struct scx_sched *sch) {} 86 static inline s32 scx_alloc_pshards(struct scx_sched *sch) { return 0; } 87 static inline void scx_init_root_caps(struct scx_sched *sch) {} 88 static inline void scx_process_sync_ecaps(struct rq *rq, struct task_struct *prev) {} 89 static inline void scx_unbypass_replay_ecaps(struct rq *rq, struct scx_sched *sch) {} 90 static inline void scx_online_ecaps(struct rq *rq) {} 91 static inline void scx_offline_ecaps(struct rq *rq) {} 92 static inline void scx_discard_ecaps_to_sync(s32 cpu, struct scx_sched_pcpu *pcpu) {} 93 static inline void scx_discard_stale_ecaps_syncs(void) {} 94 static 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; } 95 static inline bool scx_task_reenq_on_cap_revoke(struct rq *rq, struct task_struct *p) { return false; } 96 static inline void scx_reenq_reject(struct rq *rq) {} 97 static inline void scx_rescue_charge(struct rq *rq, s64 delta_exec) {} 98 static inline void scx_rescue_end(struct rq *rq) {} 99 static inline bool scx_rescue_keep(struct rq *rq, struct task_struct *p) { return false; } 100 static inline void scx_rescue_flush(struct rq *rq) {} 101 static inline void scx_rescue_dump(struct seq_buf *s, struct rq *rq) {} 102 static inline void scx_rescue_set_knobs(struct scx_sched *sch) {} 103 static inline void scx_rescue_init(struct rq *rq) {} 104 static 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 */ 131 static 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 */ 154 static 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 */ 165 static 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 */ 173 static 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 */ 188 static 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 */ 200 static 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 */ 213 static 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 */ 224 225 static inline u64 scx_missing_caps(struct scx_sched *sch, s32 cpu, u64 needed) { return 0; } 226 static inline u64 scx_caps_for_preempt(struct scx_sched *sch, struct rq *rq, u64 enq_flags) { return 0; } 227 static inline bool scx_task_can_stay_on_cpu(struct rq *rq, struct task_struct *p) { return true; } 228 static 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 */ 233