1 // SPDX-License-Identifier: GPL-2.0 2 #include "sched.h" 3 4 /* 5 * stop-task scheduling class. 6 * 7 * The stop task is the highest priority task in the system, it preempts 8 * everything and will be preempted by nothing. 9 * 10 * See kernel/stop_machine.c 11 */ 12 13 #ifdef CONFIG_SMP 14 static int 15 select_task_rq_stop(struct task_struct *p, int cpu, int sd_flag, int flags) 16 { 17 return task_cpu(p); /* stop tasks as never migrate */ 18 } 19 #endif /* CONFIG_SMP */ 20 21 static void 22 check_preempt_curr_stop(struct rq *rq, struct task_struct *p, int flags) 23 { 24 /* we're never preempted */ 25 } 26 27 static struct task_struct * 28 pick_next_task_stop(struct rq *rq, struct task_struct *prev, struct rq_flags *rf) 29 { 30 struct task_struct *stop = rq->stop; 31 32 if (!stop || !task_on_rq_queued(stop)) 33 return NULL; 34 35 put_prev_task(rq, prev); 36 37 stop->se.exec_start = rq_clock_task(rq); 38 39 return stop; 40 } 41 42 static void 43 enqueue_task_stop(struct rq *rq, struct task_struct *p, int flags) 44 { 45 add_nr_running(rq, 1); 46 } 47 48 static void 49 dequeue_task_stop(struct rq *rq, struct task_struct *p, int flags) 50 { 51 sub_nr_running(rq, 1); 52 } 53 54 static void yield_task_stop(struct rq *rq) 55 { 56 BUG(); /* the stop task should never yield, its pointless. */ 57 } 58 59 static void put_prev_task_stop(struct rq *rq, struct task_struct *prev) 60 { 61 struct task_struct *curr = rq->curr; 62 u64 delta_exec; 63 64 delta_exec = rq_clock_task(rq) - curr->se.exec_start; 65 if (unlikely((s64)delta_exec < 0)) 66 delta_exec = 0; 67 68 schedstat_set(curr->se.statistics.exec_max, 69 max(curr->se.statistics.exec_max, delta_exec)); 70 71 curr->se.sum_exec_runtime += delta_exec; 72 account_group_exec_runtime(curr, delta_exec); 73 74 curr->se.exec_start = rq_clock_task(rq); 75 cgroup_account_cputime(curr, delta_exec); 76 } 77 78 static void task_tick_stop(struct rq *rq, struct task_struct *curr, int queued) 79 { 80 } 81 82 static void set_curr_task_stop(struct rq *rq) 83 { 84 struct task_struct *stop = rq->stop; 85 86 stop->se.exec_start = rq_clock_task(rq); 87 } 88 89 static void switched_to_stop(struct rq *rq, struct task_struct *p) 90 { 91 BUG(); /* its impossible to change to this class */ 92 } 93 94 static void 95 prio_changed_stop(struct rq *rq, struct task_struct *p, int oldprio) 96 { 97 BUG(); /* how!?, what priority? */ 98 } 99 100 static unsigned int 101 get_rr_interval_stop(struct rq *rq, struct task_struct *task) 102 { 103 return 0; 104 } 105 106 static void update_curr_stop(struct rq *rq) 107 { 108 } 109 110 /* 111 * Simple, special scheduling class for the per-CPU stop tasks: 112 */ 113 const struct sched_class stop_sched_class = { 114 .next = &dl_sched_class, 115 116 .enqueue_task = enqueue_task_stop, 117 .dequeue_task = dequeue_task_stop, 118 .yield_task = yield_task_stop, 119 120 .check_preempt_curr = check_preempt_curr_stop, 121 122 .pick_next_task = pick_next_task_stop, 123 .put_prev_task = put_prev_task_stop, 124 125 #ifdef CONFIG_SMP 126 .select_task_rq = select_task_rq_stop, 127 .set_cpus_allowed = set_cpus_allowed_common, 128 #endif 129 130 .set_curr_task = set_curr_task_stop, 131 .task_tick = task_tick_stop, 132 133 .get_rr_interval = get_rr_interval_stop, 134 135 .prio_changed = prio_changed_stop, 136 .switched_to = switched_to_stop, 137 .update_curr = update_curr_stop, 138 }; 139