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 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)
  63 {
  64         requeue_task_rt(rq, rq->curr);
  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 #ifdef CONFIG_SMP
 102 /*
 103  * Load-balancing iterator. Note: while the runqueue stays locked
 104  * during the whole iteration, the current task might be
 105  * dequeued so the iterator has to be dequeue-safe. Here we
 106  * achieve that by always pre-iterating before returning
 107  * the current task:
 108  */
 109 static struct task_struct *load_balance_start_rt(void *arg)
 110 {
 111         struct rq *rq = arg;
 112         struct rt_prio_array *array = &rq->rt.active;
 113         struct list_head *head, *curr;
 114         struct task_struct *p;
 115         int idx;
 116
 117         idx = sched_find_first_bit(array->bitmap);
 118         if (idx >= MAX_RT_PRIO)
 119                 return NULL;
 120
 121         head = array->queue + idx;
 122         curr = head->prev;
 123
 124         p = list_entry(curr, struct task_struct, run_list);
 125
 126         curr = curr->prev;
 127
 128         rq->rt.rt_load_balance_idx = idx;
 129         rq->rt.rt_load_balance_head = head;
 130         rq->rt.rt_load_balance_curr = curr;
 131
 132         return p;
 133 }
 134
 135 static struct task_struct *load_balance_next_rt(void *arg)
 136 {
 137         struct rq *rq = arg;
 138         struct rt_prio_array *array = &rq->rt.active;
 139         struct list_head *head, *curr;
 140         struct task_struct *p;
 141         int idx;
 142
 143         idx = rq->rt.rt_load_balance_idx;
 144         head = rq->rt.rt_load_balance_head;
 145         curr = rq->rt.rt_load_balance_curr;
 146
 147         /*
 148          * If we arrived back to the head again then
 149          * iterate to the next queue (if any):
 150          */
 151         if (unlikely(head == curr)) {
 152                 int next_idx = find_next_bit(array->bitmap, MAX_RT_PRIO, idx+1);
 153
 154                 if (next_idx >= MAX_RT_PRIO)
 155                         return NULL;
 156
 157                 idx = next_idx;
 158                 head = array->queue + idx;
 159                 curr = head->prev;
 160
 161                 rq->rt.rt_load_balance_idx = idx;
 162                 rq->rt.rt_load_balance_head = head;
 163         }
 164
 165         p = list_entry(curr, struct task_struct, run_list);
 166
 167         curr = curr->prev;
 168
 169         rq->rt.rt_load_balance_curr = curr;
 170
 171         return p;
 172 }
 173
 174 static unsigned long
 175 load_balance_rt(struct rq *this_rq, int this_cpu, struct rq *busiest,
 176                 unsigned long max_load_move,
 177                 struct sched_domain *sd, enum cpu_idle_type idle,
 178                 int *all_pinned, int *this_best_prio)
 179 {
 180         struct rq_iterator rt_rq_iterator;
 181
 182         rt_rq_iterator.start = load_balance_start_rt;
 183         rt_rq_iterator.next = load_balance_next_rt;
 184         /* pass 'busiest' rq argument into
 185          * load_balance_[start|next]_rt iterators
 186          */
 187         rt_rq_iterator.arg = busiest;
 188
 189         return balance_tasks(this_rq, this_cpu, busiest, max_load_move, sd,
 190                              idle, all_pinned, this_best_prio, &rt_rq_iterator);
 191 }
 192
 193 static int
 194 move_one_task_rt(struct rq *this_rq, int this_cpu, struct rq *busiest,
 195                  struct sched_domain *sd, enum cpu_idle_type idle)
 196 {
 197         struct rq_iterator rt_rq_iterator;
 198
 199         rt_rq_iterator.start = load_balance_start_rt;
 200         rt_rq_iterator.next = load_balance_next_rt;
 201         rt_rq_iterator.arg = busiest;
 202
 203         return iter_move_one_task(this_rq, this_cpu, busiest, sd, idle,
 204                                   &rt_rq_iterator);
 205 }
 206 #endif
 207
 208 static void task_tick_rt(struct rq *rq, struct task_struct *p)
 209 {
 210         /*
 211          * RR tasks need a special form of timeslice management.
 212          * FIFO tasks have no timeslices.
 213          */
 214         if (p->policy != SCHED_RR)
 215                 return;
 216
 217         if (--p->time_slice)
 218                 return;
 219
 220         p->time_slice = DEF_TIMESLICE;
 221
 222         /*
 223          * Requeue to the end of queue if we are not the only element
 224          * on the queue:
 225          */
 226         if (p->run_list.prev != p->run_list.next) {
 227                 requeue_task_rt(rq, p);
 228                 set_tsk_need_resched(p);
 229         }
 230 }
 231
 232 static void set_curr_task_rt(struct rq *rq)
 233 {
 234         struct task_struct *p = rq->curr;
 235
 236         p->se.exec_start = rq->clock;
 237 }
 238
 239 const struct sched_class rt_sched_class = {
 240         .next                   = &fair_sched_class,
 241         .enqueue_task           = enqueue_task_rt,
 242         .dequeue_task           = dequeue_task_rt,
 243         .yield_task             = yield_task_rt,
 244
 245         .check_preempt_curr     = check_preempt_curr_rt,
 246
 247         .pick_next_task         = pick_next_task_rt,
 248         .put_prev_task          = put_prev_task_rt,
 249
 250 #ifdef CONFIG_SMP
 251         .load_balance           = load_balance_rt,
 252         .move_one_task          = move_one_task_rt,
 253 #endif
 254
 255         .set_curr_task          = set_curr_task_rt,
 256         .task_tick              = task_tick_rt,
 257 };