kernel/sched_rt.c

   1 /*
   2  * Real-Time Scheduling Class (mapped to the SCHED_FIFO and SCHED_RR
   3  * policies)
   4  */
   5
   6 /*
   7  * Update the current task's runtime statistics. Skip current tasks that
   8  * are not in our scheduling class.
   9  */
  10 static inline void update_curr_rt(struct rq *rq)
  11 {
  12         struct task_struct *curr = rq->curr;
  13         u64 delta_exec;
  14
  15         if (!task_has_rt_policy(curr))
  16                 return;
  17
  18         delta_exec = rq->clock - curr->se.exec_start;
  19         if (unlikely((s64)delta_exec < 0))
  20                 delta_exec = 0;
  21
  22         schedstat_set(curr->se.exec_max, max(curr->se.exec_max, delta_exec));
  23
  24         curr->se.sum_exec_runtime += delta_exec;
  25         curr->se.exec_start = rq->clock;
  26 }
  27
  28 static void enqueue_task_rt(struct rq *rq, struct task_struct *p, int wakeup)
  29 {
  30         struct rt_prio_array *array = &rq->rt.active;
  31
  32         list_add_tail(&p->run_list, array->queue + p->prio);
  33         __set_bit(p->prio, array->bitmap);
  34 }
  35
  36 /*
  37  * Adding/removing a task to/from a priority array:
  38  */
  39 static void dequeue_task_rt(struct rq *rq, struct task_struct *p, int sleep)
  40 {
  41         struct rt_prio_array *array = &rq->rt.active;
  42
  43         update_curr_rt(rq);
  44
  45         list_del(&p->run_list);
  46         if (list_empty(array->queue + p->prio))
  47                 __clear_bit(p->prio, array->bitmap);
  48 }
  49
  50 /*
  51  * Put task to the end of the run list without the overhead of dequeue
  52  * followed by enqueue.
  53  */
  54 static void requeue_task_rt(struct rq *rq, struct task_struct *p)
  55 {
  56         struct rt_prio_array *array = &rq->rt.active;
  57
  58         list_move_tail(&p->run_list, array->queue + p->prio);
  59 }
  60
  61 static void
  62 yield_task_rt(struct rq *rq, struct task_struct *p)
  63 {
  64         requeue_task_rt(rq, p);
  65 }
  66
  67 /*
  68  * Preempt the current task with a newly woken task if needed:
  69  */
  70 static void check_preempt_curr_rt(struct rq *rq, struct task_struct *p)
  71 {
  72         if (p->prio < rq->curr->prio)
  73                 resched_task(rq->curr);
  74 }
  75
  76 static struct task_struct *pick_next_task_rt(struct rq *rq)
  77 {
  78         struct rt_prio_array *array = &rq->rt.active;
  79         struct task_struct *next;
  80         struct list_head *queue;
  81         int idx;
  82
  83         idx = sched_find_first_bit(array->bitmap);
  84         if (idx >= MAX_RT_PRIO)
  85                 return NULL;
  86
  87         queue = array->queue + idx;
  88         next = list_entry(queue->next, struct task_struct, run_list);
  89
  90         next->se.exec_start = rq->clock;
  91
  92         return next;
  93 }
  94
  95 static void put_prev_task_rt(struct rq *rq, struct task_struct *p)
  96 {
  97         update_curr_rt(rq);
  98         p->se.exec_start = 0;
  99 }
 100
 101 /*
 102  * Load-balancing iterator. Note: while the runqueue stays locked
 103  * during the whole iteration, the current task might be
 104  * dequeued so the iterator has to be dequeue-safe. Here we
 105  * achieve that by always pre-iterating before returning
 106  * the current task:
 107  */
 108 static struct task_struct *load_balance_start_rt(void *arg)
 109 {
 110         struct rq *rq = arg;
 111         struct rt_prio_array *array = &rq->rt.active;
 112         struct list_head *head, *curr;
 113         struct task_struct *p;
 114         int idx;
 115
 116         idx = sched_find_first_bit(array->bitmap);
 117         if (idx >= MAX_RT_PRIO)
 118                 return NULL;
 119
 120         head = array->queue + idx;
 121         curr = head->prev;
 122
 123         p = list_entry(curr, struct task_struct, run_list);
 124
 125         curr = curr->prev;
 126
 127         rq->rt.rt_load_balance_idx = idx;
 128         rq->rt.rt_load_balance_head = head;
 129         rq->rt.rt_load_balance_curr = curr;
 130
 131         return p;
 132 }
 133
 134 static struct task_struct *load_balance_next_rt(void *arg)
 135 {
 136         struct rq *rq = arg;
 137         struct rt_prio_array *array = &rq->rt.active;
 138         struct list_head *head, *curr;
 139         struct task_struct *p;
 140         int idx;
 141
 142         idx = rq->rt.rt_load_balance_idx;
 143         head = rq->rt.rt_load_balance_head;
 144         curr = rq->rt.rt_load_balance_curr;
 145
 146         /*
 147          * If we arrived back to the head again then
 148          * iterate to the next queue (if any):
 149          */
 150         if (unlikely(head == curr)) {
 151                 int next_idx = find_next_bit(array->bitmap, MAX_RT_PRIO, idx+1);
 152
 153                 if (next_idx >= MAX_RT_PRIO)
 154                         return NULL;
 155
 156                 idx = next_idx;
 157                 head = array->queue + idx;
 158                 curr = head->prev;
 159
 160                 rq->rt.rt_load_balance_idx = idx;
 161                 rq->rt.rt_load_balance_head = head;
 162         }
 163
 164         p = list_entry(curr, struct task_struct, run_list);
 165
 166         curr = curr->prev;
 167
 168         rq->rt.rt_load_balance_curr = curr;
 169
 170         return p;
 171 }
 172
 173 static unsigned long
 174 load_balance_rt(struct rq *this_rq, int this_cpu, struct rq *busiest,
 175                         unsigned long max_nr_move, unsigned long max_load_move,
 176                         struct sched_domain *sd, enum cpu_idle_type idle,
 177                         int *all_pinned, int *this_best_prio)
 178 {
 179         int nr_moved;
 180         struct rq_iterator rt_rq_iterator;
 181         unsigned long load_moved;
 182
 183         rt_rq_iterator.start = load_balance_start_rt;
 184         rt_rq_iterator.next = load_balance_next_rt;
 185         /* pass 'busiest' rq argument into
 186          * load_balance_[start|next]_rt iterators
 187          */
 188         rt_rq_iterator.arg = busiest;
 189
 190         nr_moved = balance_tasks(this_rq, this_cpu, busiest, max_nr_move,
 191                         max_load_move, sd, idle, all_pinned, &load_moved,
 192                         this_best_prio, &rt_rq_iterator);
 193
 194         return load_moved;
 195 }
 196
 197 static void task_tick_rt(struct rq *rq, struct task_struct *p)
 198 {
 199         /*
 200          * RR tasks need a special form of timeslice management.
 201          * FIFO tasks have no timeslices.
 202          */
 203         if (p->policy != SCHED_RR)
 204                 return;
 205
 206         if (--p->time_slice)
 207                 return;
 208
 209         p->time_slice = static_prio_timeslice(p->static_prio);
 210
 211         /*
 212          * Requeue to the end of queue if we are not the only element
 213          * on the queue:
 214          */
 215         if (p->run_list.prev != p->run_list.next) {
 216                 requeue_task_rt(rq, p);
 217                 set_tsk_need_resched(p);
 218         }
 219 }
 220
 221 static struct sched_class rt_sched_class __read_mostly = {
 222         .enqueue_task           = enqueue_task_rt,
 223         .dequeue_task           = dequeue_task_rt,
 224         .yield_task             = yield_task_rt,
 225
 226         .check_preempt_curr     = check_preempt_curr_rt,
 227
 228         .pick_next_task         = pick_next_task_rt,
 229         .put_prev_task          = put_prev_task_rt,
 230
 231         .load_balance           = load_balance_rt,
 232
 233         .task_tick              = task_tick_rt,
 234 };