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