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_task_stop(struct rq *rq) 38 { 39 if (!sched_stop_runnable(rq)) 40 return NULL; 41 42 return rq->stop; 43 } 44 45 static struct task_struct *pick_next_task_stop(struct rq *rq) 46 { 47 struct task_struct *p = pick_task_stop(rq); 48 49 if (p) 50 set_next_task_stop(rq, p, true); 51 52 return p; 53 } 54 55 static void 56 enqueue_task_stop(struct rq *rq, struct task_struct *p, int flags) 57 { 58 add_nr_running(rq, 1); 59 } 60 61 static void 62 dequeue_task_stop(struct rq *rq, struct task_struct *p, int flags) 63 { 64 sub_nr_running(rq, 1); 65 } 66 67 static void yield_task_stop(struct rq *rq) 68 { 69 BUG(); /* the stop task should never yield, its pointless. */ 70 } 71 72 static void put_prev_task_stop(struct rq *rq, struct task_struct *prev) 73 { 74 struct task_struct *curr = rq->curr; 75 u64 delta_exec; 76 77 delta_exec = rq_clock_task(rq) - curr->se.exec_start; 78 if (unlikely((s64)delta_exec < 0)) 79 delta_exec = 0; 80 81 schedstat_set(curr->se.statistics.exec_max, 82 max(curr->se.statistics.exec_max, delta_exec)); 83 84 curr->se.sum_exec_runtime += delta_exec; 85 account_group_exec_runtime(curr, delta_exec); 86 87 curr->se.exec_start = rq_clock_task(rq); 88 cgroup_account_cputime(curr, delta_exec); 89 } 90 91 /* 92 * scheduler tick hitting a task of our scheduling class. 93 * 94 * NOTE: This function can be called remotely by the tick offload that 95 * goes along full dynticks. Therefore no local assumption can be made 96 * and everything must be accessed through the @rq and @curr passed in 97 * parameters. 98 */ 99 static void task_tick_stop(struct rq *rq, struct task_struct *curr, int queued) 100 { 101 } 102 103 static void switched_to_stop(struct rq *rq, struct task_struct *p) 104 { 105 BUG(); /* its impossible to change to this class */ 106 } 107 108 static void 109 prio_changed_stop(struct rq *rq, struct task_struct *p, int oldprio) 110 { 111 BUG(); /* how!?, what priority? */ 112 } 113 114 static void update_curr_stop(struct rq *rq) 115 { 116 } 117 118 /* 119 * Simple, special scheduling class for the per-CPU stop tasks: 120 */ 121 DEFINE_SCHED_CLASS(stop) = { 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 .set_next_task = set_next_task_stop, 132 133 #ifdef CONFIG_SMP 134 .balance = balance_stop, 135 .pick_task = pick_task_stop, 136 .select_task_rq = select_task_rq_stop, 137 .set_cpus_allowed = set_cpus_allowed_common, 138 #endif 139 140 .task_tick = task_tick_stop, 141 142 .prio_changed = prio_changed_stop, 143 .switched_to = switched_to_stop, 144 .update_curr = update_curr_stop, 145 }; 146