1 // SPDX-License-Identifier: GPL-2.0 2 /* 3 * stop-task scheduling class. 4 * 5 * The stop task is the highest priority task in the system, it preempts 6 * everything and will be preempted by nothing. 7 * 8 * See kernel/stop_machine.c 9 */ 10 #include "sched.h" 11 12 #ifdef CONFIG_SMP 13 static int 14 select_task_rq_stop(struct task_struct *p, int cpu, int sd_flag, int flags) 15 { 16 return task_cpu(p); /* stop tasks as never migrate */ 17 } 18 #endif /* CONFIG_SMP */ 19 20 static void 21 check_preempt_curr_stop(struct rq *rq, struct task_struct *p, int flags) 22 { 23 /* we're never preempted */ 24 } 25 26 static struct task_struct * 27 pick_next_task_stop(struct rq *rq, struct task_struct *prev, struct rq_flags *rf) 28 { 29 struct task_struct *stop = rq->stop; 30 31 if (!stop || !task_on_rq_queued(stop)) 32 return NULL; 33 34 put_prev_task(rq, prev); 35 36 stop->se.exec_start = rq_clock_task(rq); 37 38 return stop; 39 } 40 41 static void 42 enqueue_task_stop(struct rq *rq, struct task_struct *p, int flags) 43 { 44 add_nr_running(rq, 1); 45 } 46 47 static void 48 dequeue_task_stop(struct rq *rq, struct task_struct *p, int flags) 49 { 50 sub_nr_running(rq, 1); 51 } 52 53 static void yield_task_stop(struct rq *rq) 54 { 55 BUG(); /* the stop task should never yield, its pointless. */ 56 } 57 58 static void put_prev_task_stop(struct rq *rq, struct task_struct *prev) 59 { 60 struct task_struct *curr = rq->curr; 61 u64 delta_exec; 62 63 delta_exec = rq_clock_task(rq) - curr->se.exec_start; 64 if (unlikely((s64)delta_exec < 0)) 65 delta_exec = 0; 66 67 schedstat_set(curr->se.statistics.exec_max, 68 max(curr->se.statistics.exec_max, delta_exec)); 69 70 curr->se.sum_exec_runtime += delta_exec; 71 account_group_exec_runtime(curr, delta_exec); 72 73 curr->se.exec_start = rq_clock_task(rq); 74 cgroup_account_cputime(curr, delta_exec); 75 } 76 77 /* 78 * scheduler tick hitting a task of our scheduling class. 79 * 80 * NOTE: This function can be called remotely by the tick offload that 81 * goes along full dynticks. Therefore no local assumption can be made 82 * and everything must be accessed through the @rq and @curr passed in 83 * parameters. 84 */ 85 static void task_tick_stop(struct rq *rq, struct task_struct *curr, int queued) 86 { 87 } 88 89 static void set_curr_task_stop(struct rq *rq) 90 { 91 struct task_struct *stop = rq->stop; 92 93 stop->se.exec_start = rq_clock_task(rq); 94 } 95 96 static void switched_to_stop(struct rq *rq, struct task_struct *p) 97 { 98 BUG(); /* its impossible to change to this class */ 99 } 100 101 static void 102 prio_changed_stop(struct rq *rq, struct task_struct *p, int oldprio) 103 { 104 BUG(); /* how!?, what priority? */ 105 } 106 107 static unsigned int 108 get_rr_interval_stop(struct rq *rq, struct task_struct *task) 109 { 110 return 0; 111 } 112 113 static void update_curr_stop(struct rq *rq) 114 { 115 } 116 117 /* 118 * Simple, special scheduling class for the per-CPU stop tasks: 119 */ 120 const struct sched_class stop_sched_class = { 121 .next = &dl_sched_class, 122 123 .enqueue_task = enqueue_task_stop, 124 .dequeue_task = dequeue_task_stop, 125 .yield_task = yield_task_stop, 126 127 .check_preempt_curr = check_preempt_curr_stop, 128 129 .pick_next_task = pick_next_task_stop, 130 .put_prev_task = put_prev_task_stop, 131 132 #ifdef CONFIG_SMP 133 .select_task_rq = select_task_rq_stop, 134 .set_cpus_allowed = set_cpus_allowed_common, 135 #endif 136 137 .set_curr_task = set_curr_task_stop, 138 .task_tick = task_tick_stop, 139 140 .get_rr_interval = get_rr_interval_stop, 141 142 .prio_changed = prio_changed_stop, 143 .switched_to = switched_to_stop, 144 .update_curr = update_curr_stop, 145 }; 146