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 void set_next_task_stop(struct rq *rq, struct task_struct *stop) 27 { 28 stop->se.exec_start = rq_clock_task(rq); 29 } 30 31 static struct task_struct * 32 pick_next_task_stop(struct rq *rq, struct task_struct *prev, struct rq_flags *rf) 33 { 34 struct task_struct *stop = rq->stop; 35 36 if (!stop || !task_on_rq_queued(stop)) 37 return NULL; 38 39 put_prev_task(rq, prev); 40 set_next_task_stop(rq, stop); 41 42 return stop; 43 } 44 45 static void 46 enqueue_task_stop(struct rq *rq, struct task_struct *p, int flags) 47 { 48 add_nr_running(rq, 1); 49 } 50 51 static void 52 dequeue_task_stop(struct rq *rq, struct task_struct *p, int flags) 53 { 54 sub_nr_running(rq, 1); 55 } 56 57 static void yield_task_stop(struct rq *rq) 58 { 59 BUG(); /* the stop task should never yield, its pointless. */ 60 } 61 62 static void put_prev_task_stop(struct rq *rq, struct task_struct *prev, struct rq_flags *rf) 63 { 64 struct task_struct *curr = rq->curr; 65 u64 delta_exec; 66 67 delta_exec = rq_clock_task(rq) - curr->se.exec_start; 68 if (unlikely((s64)delta_exec < 0)) 69 delta_exec = 0; 70 71 schedstat_set(curr->se.statistics.exec_max, 72 max(curr->se.statistics.exec_max, delta_exec)); 73 74 curr->se.sum_exec_runtime += delta_exec; 75 account_group_exec_runtime(curr, delta_exec); 76 77 curr->se.exec_start = rq_clock_task(rq); 78 cgroup_account_cputime(curr, delta_exec); 79 } 80 81 /* 82 * scheduler tick hitting a task of our scheduling class. 83 * 84 * NOTE: This function can be called remotely by the tick offload that 85 * goes along full dynticks. Therefore no local assumption can be made 86 * and everything must be accessed through the @rq and @curr passed in 87 * parameters. 88 */ 89 static void task_tick_stop(struct rq *rq, struct task_struct *curr, int queued) 90 { 91 } 92 93 static void switched_to_stop(struct rq *rq, struct task_struct *p) 94 { 95 BUG(); /* its impossible to change to this class */ 96 } 97 98 static void 99 prio_changed_stop(struct rq *rq, struct task_struct *p, int oldprio) 100 { 101 BUG(); /* how!?, what priority? */ 102 } 103 104 static unsigned int 105 get_rr_interval_stop(struct rq *rq, struct task_struct *task) 106 { 107 return 0; 108 } 109 110 static void update_curr_stop(struct rq *rq) 111 { 112 } 113 114 /* 115 * Simple, special scheduling class for the per-CPU stop tasks: 116 */ 117 const struct sched_class stop_sched_class = { 118 .next = &dl_sched_class, 119 120 .enqueue_task = enqueue_task_stop, 121 .dequeue_task = dequeue_task_stop, 122 .yield_task = yield_task_stop, 123 124 .check_preempt_curr = check_preempt_curr_stop, 125 126 .pick_next_task = pick_next_task_stop, 127 .put_prev_task = put_prev_task_stop, 128 .set_next_task = set_next_task_stop, 129 130 #ifdef CONFIG_SMP 131 .select_task_rq = select_task_rq_stop, 132 .set_cpus_allowed = set_cpus_allowed_common, 133 #endif 134 135 .task_tick = task_tick_stop, 136 137 .get_rr_interval = get_rr_interval_stop, 138 139 .prio_changed = prio_changed_stop, 140 .switched_to = switched_to_stop, 141 .update_curr = update_curr_stop, 142 }; 143