sched, doc: Update sched-design-CFS.txt
[linux-2.6.git] / kernel / sched_stoptask.c
1 /*
2  * stop-task scheduling class.
3  *
4  * The stop task is the highest priority task in the system, it preempts
5  * everything and will be preempted by nothing.
6  *
7  * See kernel/stop_machine.c
8  */
9
10 #ifdef CONFIG_SMP
11 static int
12 select_task_rq_stop(struct rq *rq, struct task_struct *p,
13                     int sd_flag, int flags)
14 {
15         return task_cpu(p); /* stop tasks as never migrate */
16 }
17 #endif /* CONFIG_SMP */
18
19 static void
20 check_preempt_curr_stop(struct rq *rq, struct task_struct *p, int flags)
21 {
22         /* we're never preempted */
23 }
24
25 static struct task_struct *pick_next_task_stop(struct rq *rq)
26 {
27         struct task_struct *stop = rq->stop;
28
29         if (stop && stop->se.on_rq)
30                 return stop;
31
32         return NULL;
33 }
34
35 static void
36 enqueue_task_stop(struct rq *rq, struct task_struct *p, int flags)
37 {
38 }
39
40 static void
41 dequeue_task_stop(struct rq *rq, struct task_struct *p, int flags)
42 {
43 }
44
45 static void yield_task_stop(struct rq *rq)
46 {
47         BUG(); /* the stop task should never yield, its pointless. */
48 }
49
50 static void put_prev_task_stop(struct rq *rq, struct task_struct *prev)
51 {
52 }
53
54 static void task_tick_stop(struct rq *rq, struct task_struct *curr, int queued)
55 {
56 }
57
58 static void set_curr_task_stop(struct rq *rq)
59 {
60 }
61
62 static void switched_to_stop(struct rq *rq, struct task_struct *p)
63 {
64         BUG(); /* its impossible to change to this class */
65 }
66
67 static void
68 prio_changed_stop(struct rq *rq, struct task_struct *p, int oldprio)
69 {
70         BUG(); /* how!?, what priority? */
71 }
72
73 static unsigned int
74 get_rr_interval_stop(struct rq *rq, struct task_struct *task)
75 {
76         return 0;
77 }
78
79 /*
80  * Simple, special scheduling class for the per-CPU stop tasks:
81  */
82 static const struct sched_class stop_sched_class = {
83         .next                   = &rt_sched_class,
84
85         .enqueue_task           = enqueue_task_stop,
86         .dequeue_task           = dequeue_task_stop,
87         .yield_task             = yield_task_stop,
88
89         .check_preempt_curr     = check_preempt_curr_stop,
90
91         .pick_next_task         = pick_next_task_stop,
92         .put_prev_task          = put_prev_task_stop,
93
94 #ifdef CONFIG_SMP
95         .select_task_rq         = select_task_rq_stop,
96 #endif
97
98         .set_curr_task          = set_curr_task_stop,
99         .task_tick              = task_tick_stop,
100
101         .get_rr_interval        = get_rr_interval_stop,
102
103         .prio_changed           = prio_changed_stop,
104         .switched_to            = switched_to_stop,
105 };