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         cpuacct_charge(curr, delta_exec);
  27 }
  28
  29 static void enqueue_task_rt(struct rq *rq, struct task_struct *p, int wakeup)
  30 {
  31         struct rt_prio_array *array = &rq->rt.active;
  32
  33         list_add_tail(&p->run_list, array->queue + p->prio);
  34         __set_bit(p->prio, array->bitmap);
  35 }
  36
  37 /*
  38  * Adding/removing a task to/from a priority array:
  39  */
  40 static void dequeue_task_rt(struct rq *rq, struct task_struct *p, int sleep)
  41 {
  42         struct rt_prio_array *array = &rq->rt.active;
  43
  44         update_curr_rt(rq);
  45
  46         list_del(&p->run_list);
  47         if (list_empty(array->queue + p->prio))
  48                 __clear_bit(p->prio, array->bitmap);
  49 }
  50
  51 /*
  52  * Put task to the end of the run list without the overhead of dequeue
  53  * followed by enqueue.
  54  */
  55 static void requeue_task_rt(struct rq *rq, struct task_struct *p)
  56 {
  57         struct rt_prio_array *array = &rq->rt.active;
  58
  59         list_move_tail(&p->run_list, array->queue + p->prio);
  60 }
  61
  62 static void
  63 yield_task_rt(struct rq *rq)
  64 {
  65         requeue_task_rt(rq, rq->curr);
  66 }
  67
  68 /*
  69  * Preempt the current task with a newly woken task if needed:
  70  */
  71 static void check_preempt_curr_rt(struct rq *rq, struct task_struct *p)
  72 {
  73         if (p->prio < rq->curr->prio)
  74                 resched_task(rq->curr);
  75 }
  76
  77 static struct task_struct *pick_next_task_rt(struct rq *rq)
  78 {
  79         struct rt_prio_array *array = &rq->rt.active;
  80         struct task_struct *next;
  81         struct list_head *queue;
  82         int idx;
  83
  84         idx = sched_find_first_bit(array->bitmap);
  85         if (idx >= MAX_RT_PRIO)
  86                 return NULL;
  87
  88         queue = array->queue + idx;
  89         next = list_entry(queue->next, struct task_struct, run_list);
  90
  91         next->se.exec_start = rq->clock;
  92
  93         return next;
  94 }
  95
  96 static void put_prev_task_rt(struct rq *rq, struct task_struct *p)
  97 {
  98         update_curr_rt(rq);
  99         p->se.exec_start = 0;
 100 }
 101
 102 #ifdef CONFIG_SMP
 103 /*
 104  * Load-balancing iterator. Note: while the runqueue stays locked
 105  * during the whole iteration, the current task might be
 106  * dequeued so the iterator has to be dequeue-safe. Here we
 107  * achieve that by always pre-iterating before returning
 108  * the current task:
 109  */
 110 static struct task_struct *load_balance_start_rt(void *arg)
 111 {
 112         struct rq *rq = arg;
 113         struct rt_prio_array *array = &rq->rt.active;
 114         struct list_head *head, *curr;
 115         struct task_struct *p;
 116         int idx;
 117
 118         idx = sched_find_first_bit(array->bitmap);
 119         if (idx >= MAX_RT_PRIO)
 120                 return NULL;
 121
 122         head = array->queue + idx;
 123         curr = head->prev;
 124
 125         p = list_entry(curr, struct task_struct, run_list);
 126
 127         curr = curr->prev;
 128
 129         rq->rt.rt_load_balance_idx = idx;
 130         rq->rt.rt_load_balance_head = head;
 131         rq->rt.rt_load_balance_curr = curr;
 132
 133         return p;
 134 }
 135
 136 static struct task_struct *load_balance_next_rt(void *arg)
 137 {
 138         struct rq *rq = arg;
 139         struct rt_prio_array *array = &rq->rt.active;
 140         struct list_head *head, *curr;
 141         struct task_struct *p;
 142         int idx;
 143
 144         idx = rq->rt.rt_load_balance_idx;
 145         head = rq->rt.rt_load_balance_head;
 146         curr = rq->rt.rt_load_balance_curr;
 147
 148         /*
 149          * If we arrived back to the head again then
 150          * iterate to the next queue (if any):
 151          */
 152         if (unlikely(head == curr)) {
 153                 int next_idx = find_next_bit(array->bitmap, MAX_RT_PRIO, idx+1);
 154
 155                 if (next_idx >= MAX_RT_PRIO)
 156                         return NULL;
 157
 158                 idx = next_idx;
 159                 head = array->queue + idx;
 160                 curr = head->prev;
 161
 162                 rq->rt.rt_load_balance_idx = idx;
 163                 rq->rt.rt_load_balance_head = head;
 164         }
 165
 166         p = list_entry(curr, struct task_struct, run_list);
 167
 168         curr = curr->prev;
 169
 170         rq->rt.rt_load_balance_curr = curr;
 171
 172         return p;
 173 }
 174
 175 static unsigned long
 176 load_balance_rt(struct rq *this_rq, int this_cpu, struct rq *busiest,
 177                 unsigned long max_load_move,
 178                 struct sched_domain *sd, enum cpu_idle_type idle,
 179                 int *all_pinned, int *this_best_prio)
 180 {
 181         struct rq_iterator rt_rq_iterator;
 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         return balance_tasks(this_rq, this_cpu, busiest, max_load_move, sd,
 191                              idle, all_pinned, this_best_prio, &rt_rq_iterator);
 192 }
 193
 194 static int
 195 move_one_task_rt(struct rq *this_rq, int this_cpu, struct rq *busiest,
 196                  struct sched_domain *sd, enum cpu_idle_type idle)
 197 {
 198         struct rq_iterator rt_rq_iterator;
 199
 200         rt_rq_iterator.start = load_balance_start_rt;
 201         rt_rq_iterator.next = load_balance_next_rt;
 202         rt_rq_iterator.arg = busiest;
 203
 204         return iter_move_one_task(this_rq, this_cpu, busiest, sd, idle,
 205                                   &rt_rq_iterator);
 206 }
 207 #endif
 208
 209 static void task_tick_rt(struct rq *rq, struct task_struct *p)
 210 {
 211         update_curr_rt(rq);
 212
 213         /*
 214          * RR tasks need a special form of timeslice management.
 215          * FIFO tasks have no timeslices.
 216          */
 217         if (p->policy != SCHED_RR)
 218                 return;
 219
 220         if (--p->time_slice)
 221                 return;
 222
 223         p->time_slice = DEF_TIMESLICE;
 224
 225         /*
 226          * Requeue to the end of queue if we are not the only element
 227          * on the queue:
 228          */
 229         if (p->run_list.prev != p->run_list.next) {
 230                 requeue_task_rt(rq, p);
 231                 set_tsk_need_resched(p);
 232         }
 233 }
 234
 235 static void set_curr_task_rt(struct rq *rq)
 236 {
 237         struct task_struct *p = rq->curr;
 238
 239         p->se.exec_start = rq->clock;
 240 }
 241
 242 const struct sched_class rt_sched_class = {
 243         .next                   = &fair_sched_class,
 244         .enqueue_task           = enqueue_task_rt,
 245         .dequeue_task           = dequeue_task_rt,
 246         .yield_task             = yield_task_rt,
 247
 248         .check_preempt_curr     = check_preempt_curr_rt,
 249
 250         .pick_next_task         = pick_next_task_rt,
 251         .put_prev_task          = put_prev_task_rt,
 252
 253 #ifdef CONFIG_SMP
 254         .load_balance           = load_balance_rt,
 255         .move_one_task          = move_one_task_rt,
 256 #endif
 257
 258         .set_curr_task          = set_curr_task_rt,
 259         .task_tick              = task_tick_rt,
 260 };