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 flags) 15 { 16 return task_cpu(p); /* stop tasks as never migrate */ 17 } 18 19 static int 20 balance_stop(struct rq *rq, struct task_struct *prev, struct rq_flags *rf) 21 { 22 return sched_stop_runnable(rq); 23 } 24 #endif /* CONFIG_SMP */ 25 26 static void 27 check_preempt_curr_stop(struct rq *rq, struct task_struct *p, int flags) 28 { 29 /* we're never preempted */ 30 } 31 32 static void set_next_task_stop(struct rq *rq, struct task_struct *stop, bool first) 33 { 34 stop->se.exec_start = rq_clock_task(rq); 35 } 36 37 static struct task_struct *pick_next_task_stop(struct rq *rq) 38 { 39 if (!sched_stop_runnable(rq)) 40 return NULL; 41 42 set_next_task_stop(rq, rq->stop, true); 43 return rq->stop; 44 } 45 46 static void 47 enqueue_task_stop(struct rq *rq, struct task_struct *p, int flags) 48 { 49 add_nr_running(rq, 1); 50 } 51 52 static void 53 dequeue_task_stop(struct rq *rq, struct task_struct *p, int flags) 54 { 55 sub_nr_running(rq, 1); 56 } 57 58 static void yield_task_stop(struct rq *rq) 59 { 60 BUG(); /* the stop task should never yield, its pointless. */ 61 } 62 63 static void put_prev_task_stop(struct rq *rq, struct task_struct *prev) 64 { 65 struct task_struct *curr = rq->curr; 66 u64 delta_exec; 67 68 delta_exec = rq_clock_task(rq) - curr->se.exec_start; 69 if (unlikely((s64)delta_exec < 0)) 70 delta_exec = 0; 71 72 schedstat_set(curr->se.statistics.exec_max, 73 max(curr->se.statistics.exec_max, delta_exec)); 74 75 curr->se.sum_exec_runtime += delta_exec; 76 account_group_exec_runtime(curr, delta_exec); 77 78 curr->se.exec_start = rq_clock_task(rq); 79 cgroup_account_cputime(curr, delta_exec); 80 } 81 82 /* 83 * scheduler tick hitting a task of our scheduling class. 84 * 85 * NOTE: This function can be called remotely by the tick offload that 86 * goes along full dynticks. Therefore no local assumption can be made 87 * and everything must be accessed through the @rq and @curr passed in 88 * parameters. 89 */ 90 static void task_tick_stop(struct rq *rq, struct task_struct *curr, int queued) 91 { 92 } 93 94 static void switched_to_stop(struct rq *rq, struct task_struct *p) 95 { 96 BUG(); /* its impossible to change to this class */ 97 } 98 99 static void 100 prio_changed_stop(struct rq *rq, struct task_struct *p, int oldprio) 101 { 102 BUG(); /* how!?, what priority? */ 103 } 104 105 static void update_curr_stop(struct rq *rq) 106 { 107 } 108 109 /* 110 * Simple, special scheduling class for the per-CPU stop tasks: 111 */ 112 DEFINE_SCHED_CLASS(stop) = { 113 114 .enqueue_task = enqueue_task_stop, 115 .dequeue_task = dequeue_task_stop, 116 .yield_task = yield_task_stop, 117 118 .check_preempt_curr = check_preempt_curr_stop, 119 120 .pick_next_task = pick_next_task_stop, 121 .put_prev_task = put_prev_task_stop, 122 .set_next_task = set_next_task_stop, 123 124 #ifdef CONFIG_SMP 125 .balance = balance_stop, 126 .select_task_rq = select_task_rq_stop, 127 .set_cpus_allowed = set_cpus_allowed_common, 128 #endif 129 130 .task_tick = task_tick_stop, 131 132 .prio_changed = prio_changed_stop, 133 .switched_to = switched_to_stop, 134 .update_curr = update_curr_stop, 135 }; 136