kernel/sched/stop_task.c

   1 #include "sched.h"
   2 #include "walt.h"
   3
   4 /*
   5  * stop-task scheduling class.
   6  *
   7  * The stop task is the highest priority task in the system, it preempts
   8  * everything and will be preempted by nothing.
   9  *
  10  * See kernel/stop_machine.c
  11  */
  12
  13 #ifdef CONFIG_SMP
  14 static int
  15 select_task_rq_stop(struct task_struct *p, int cpu, int sd_flag, int flags)
  16 {
  17         return task_cpu(p); /* stop tasks as never migrate */
  18 }
  19 #endif /* CONFIG_SMP */
  20
  21 static void
  22 check_preempt_curr_stop(struct rq *rq, struct task_struct *p, int flags)
  23 {
  24         /* we're never preempted */
  25 }
  26
  27 static struct task_struct *
  28 pick_next_task_stop(struct rq *rq, struct task_struct *prev)
  29 {
  30         struct task_struct *stop = rq->stop;
  31
  32         if (!stop || !task_on_rq_queued(stop))
  33                 return NULL;
  34
  35         put_prev_task(rq, prev);
  36
  37         stop->se.exec_start = rq_clock_task(rq);
  38
  39         return stop;
  40 }
  41
  42 static void
  43 enqueue_task_stop(struct rq *rq, struct task_struct *p, int flags)
  44 {
  45         add_nr_running(rq, 1);
  46         walt_inc_cumulative_runnable_avg(rq, p);
  47 }
  48
  49 static void
  50 dequeue_task_stop(struct rq *rq, struct task_struct *p, int flags)
  51 {
  52         sub_nr_running(rq, 1);
  53         walt_dec_cumulative_runnable_avg(rq, p);
  54 }
  55
  56 static void yield_task_stop(struct rq *rq)
  57 {
  58         BUG(); /* the stop task should never yield, its pointless. */
  59 }
  60
  61 static void put_prev_task_stop(struct rq *rq, struct task_struct *prev)
  62 {
  63         struct task_struct *curr = rq->curr;
  64         u64 delta_exec;
  65
  66         delta_exec = rq_clock_task(rq) - curr->se.exec_start;
  67         if (unlikely((s64)delta_exec < 0))
  68                 delta_exec = 0;
  69
  70         schedstat_set(curr->se.statistics.exec_max,
  71                         max(curr->se.statistics.exec_max, delta_exec));
  72
  73         curr->se.sum_exec_runtime += delta_exec;
  74         account_group_exec_runtime(curr, delta_exec);
  75
  76         curr->se.exec_start = rq_clock_task(rq);
  77         cpuacct_charge(curr, delta_exec);
  78 }
  79
  80 static void task_tick_stop(struct rq *rq, struct task_struct *curr, int queued)
  81 {
  82 }
  83
  84 static void set_curr_task_stop(struct rq *rq)
  85 {
  86         struct task_struct *stop = rq->stop;
  87
  88         stop->se.exec_start = rq_clock_task(rq);
  89 }
  90
  91 static void switched_to_stop(struct rq *rq, struct task_struct *p)
  92 {
  93         BUG(); /* its impossible to change to this class */
  94 }
  95
  96 static void
  97 prio_changed_stop(struct rq *rq, struct task_struct *p, int oldprio)
  98 {
  99         BUG(); /* how!?, what priority? */
 100 }
 101
 102 static unsigned int
 103 get_rr_interval_stop(struct rq *rq, struct task_struct *task)
 104 {
 105         return 0;
 106 }
 107
 108 static void update_curr_stop(struct rq *rq)
 109 {
 110 }
 111
 112 /*
 113  * Simple, special scheduling class for the per-CPU stop tasks:
 114  */
 115 const struct sched_class stop_sched_class = {
 116         .next                   = &dl_sched_class,
 117
 118         .enqueue_task           = enqueue_task_stop,
 119         .dequeue_task           = dequeue_task_stop,
 120         .yield_task             = yield_task_stop,
 121
 122         .check_preempt_curr     = check_preempt_curr_stop,
 123
 124         .pick_next_task         = pick_next_task_stop,
 125         .put_prev_task          = put_prev_task_stop,
 126
 127 #ifdef CONFIG_SMP
 128         .select_task_rq         = select_task_rq_stop,
 129         .set_cpus_allowed       = set_cpus_allowed_common,
 130 #endif
 131
 132         .set_curr_task          = set_curr_task_stop,
 133         .task_tick              = task_tick_stop,
 134
 135         .get_rr_interval        = get_rr_interval_stop,
 136
 137         .prio_changed           = prio_changed_stop,
 138         .switched_to            = switched_to_stop,
 139         .update_curr            = update_curr_stop,
 140 };