kernel/sched/cpudeadline.c

   1 /*
   2  *  kernel/sched/cpudl.c
   3  *
   4  *  Global CPU deadline management
   5  *
   6  *  Author: Juri Lelli <j.lelli@sssup.it>
   7  *
   8  *  This program is free software; you can redistribute it and/or
   9  *  modify it under the terms of the GNU General Public License
  10  *  as published by the Free Software Foundation; version 2
  11  *  of the License.
  12  */
  13
  14 #include <linux/gfp.h>
  15 #include <linux/kernel.h>
  16 #include "cpudeadline.h"
  17
  18 static inline int parent(int i)
  19 {
  20         return (i - 1) >> 1;
  21 }
  22
  23 static inline int left_child(int i)
  24 {
  25         return (i << 1) + 1;
  26 }
  27
  28 static inline int right_child(int i)
  29 {
  30         return (i << 1) + 2;
  31 }
  32
  33 static inline int dl_time_before(u64 a, u64 b)
  34 {
  35         return (s64)(a - b) < 0;
  36 }
  37
  38 static void cpudl_exchange(struct cpudl *cp, int a, int b)
  39 {
  40         int cpu_a = cp->elements[a].cpu, cpu_b = cp->elements[b].cpu;
  41
  42         swap(cp->elements[a], cp->elements[b]);
  43         swap(cp->cpu_to_idx[cpu_a], cp->cpu_to_idx[cpu_b]);
  44 }
  45
  46 static void cpudl_heapify(struct cpudl *cp, int idx)
  47 {
  48         int l, r, largest;
  49
  50         /* adapted from lib/prio_heap.c */
  51         while(1) {
  52                 l = left_child(idx);
  53                 r = right_child(idx);
  54                 largest = idx;
  55
  56                 if ((l < cp->size) && dl_time_before(cp->elements[idx].dl,
  57                                                         cp->elements[l].dl))
  58                         largest = l;
  59                 if ((r < cp->size) && dl_time_before(cp->elements[largest].dl,
  60                                                         cp->elements[r].dl))
  61                         largest = r;
  62                 if (largest == idx)
  63                         break;
  64
  65                 /* Push idx down the heap one level and bump one up */
  66                 cpudl_exchange(cp, largest, idx);
  67                 idx = largest;
  68         }
  69 }
  70
  71 static void cpudl_change_key(struct cpudl *cp, int idx, u64 new_dl)
  72 {
  73         WARN_ON(idx == IDX_INVALID || !cpu_present(idx));
  74
  75         if (dl_time_before(new_dl, cp->elements[idx].dl)) {
  76                 cp->elements[idx].dl = new_dl;
  77                 cpudl_heapify(cp, idx);
  78         } else {
  79                 cp->elements[idx].dl = new_dl;
  80                 while (idx > 0 && dl_time_before(cp->elements[parent(idx)].dl,
  81                                         cp->elements[idx].dl)) {
  82                         cpudl_exchange(cp, idx, parent(idx));
  83                         idx = parent(idx);
  84                 }
  85         }
  86 }
  87
  88 static inline int cpudl_maximum(struct cpudl *cp)
  89 {
  90         return cp->elements[0].cpu;
  91 }
  92
  93 /*
  94  * cpudl_find - find the best (later-dl) CPU in the system
  95  * @cp: the cpudl max-heap context
  96  * @p: the task
  97  * @later_mask: a mask to fill in with the selected CPUs (or NULL)
  98  *
  99  * Returns: int - best CPU (heap maximum if suitable)
 100  */
 101 int cpudl_find(struct cpudl *cp, struct task_struct *p,
 102                struct cpumask *later_mask)
 103 {
 104         int best_cpu = -1;
 105         const struct sched_dl_entity *dl_se = &p->dl;
 106
 107         if (later_mask && cpumask_and(later_mask, cp->free_cpus,
 108                         &p->cpus_allowed) && cpumask_and(later_mask,
 109                         later_mask, cpu_active_mask)) {
 110                 best_cpu = cpumask_any(later_mask);
 111                 goto out;
 112         } else if (cpumask_test_cpu(cpudl_maximum(cp), &p->cpus_allowed) &&
 113                         dl_time_before(dl_se->deadline, cp->elements[0].dl)) {
 114                 best_cpu = cpudl_maximum(cp);
 115                 if (later_mask)
 116                         cpumask_set_cpu(best_cpu, later_mask);
 117         }
 118
 119 out:
 120         WARN_ON(best_cpu != -1 && !cpu_present(best_cpu));
 121
 122         return best_cpu;
 123 }
 124
 125 /*
 126  * cpudl_set - update the cpudl max-heap
 127  * @cp: the cpudl max-heap context
 128  * @cpu: the target cpu
 129  * @dl: the new earliest deadline for this cpu
 130  *
 131  * Notes: assumes cpu_rq(cpu)->lock is locked
 132  *
 133  * Returns: (void)
 134  */
 135 void cpudl_set(struct cpudl *cp, int cpu, u64 dl, int is_valid)
 136 {
 137         int old_idx, new_cpu;
 138         unsigned long flags;
 139
 140         WARN_ON(!cpu_present(cpu));
 141
 142         raw_spin_lock_irqsave(&cp->lock, flags);
 143         old_idx = cp->cpu_to_idx[cpu];
 144         if (!is_valid) {
 145                 /* remove item */
 146                 if (old_idx == IDX_INVALID) {
 147                         /*
 148                          * Nothing to remove if old_idx was invalid.
 149                          * This could happen if a rq_offline_dl is
 150                          * called for a CPU without -dl tasks running.
 151                          */
 152                         goto out;
 153                 }
 154                 new_cpu = cp->elements[cp->size - 1].cpu;
 155                 cp->elements[old_idx].dl = cp->elements[cp->size - 1].dl;
 156                 cp->elements[old_idx].cpu = new_cpu;
 157                 cp->size--;
 158                 cp->cpu_to_idx[new_cpu] = old_idx;
 159                 cp->cpu_to_idx[cpu] = IDX_INVALID;
 160                 while (old_idx > 0 && dl_time_before(
 161                                 cp->elements[parent(old_idx)].dl,
 162                                 cp->elements[old_idx].dl)) {
 163                         cpudl_exchange(cp, old_idx, parent(old_idx));
 164                         old_idx = parent(old_idx);
 165                 }
 166                 cpumask_set_cpu(cpu, cp->free_cpus);
 167                 cpudl_heapify(cp, old_idx);
 168
 169                 goto out;
 170         }
 171
 172         if (old_idx == IDX_INVALID) {
 173                 cp->size++;
 174                 cp->elements[cp->size - 1].dl = 0;
 175                 cp->elements[cp->size - 1].cpu = cpu;
 176                 cp->cpu_to_idx[cpu] = cp->size - 1;
 177                 cpudl_change_key(cp, cp->size - 1, dl);
 178                 cpumask_clear_cpu(cpu, cp->free_cpus);
 179         } else {
 180                 cpudl_change_key(cp, old_idx, dl);
 181         }
 182
 183 out:
 184         raw_spin_unlock_irqrestore(&cp->lock, flags);
 185 }
 186
 187 /*
 188  * cpudl_init - initialize the cpudl structure
 189  * @cp: the cpudl max-heap context
 190  */
 191 int cpudl_init(struct cpudl *cp)
 192 {
 193         int i;
 194
 195         memset(cp, 0, sizeof(*cp));
 196         raw_spin_lock_init(&cp->lock);
 197         cp->size = 0;
 198         for (i = 0; i < NR_CPUS; i++)
 199                 cp->cpu_to_idx[i] = IDX_INVALID;
 200         if (!alloc_cpumask_var(&cp->free_cpus, GFP_KERNEL))
 201                 return -ENOMEM;
 202         cpumask_setall(cp->free_cpus);
 203
 204         return 0;
 205 }
 206
 207 /*
 208  * cpudl_cleanup - clean up the cpudl structure
 209  * @cp: the cpudl max-heap context
 210  */
 211 void cpudl_cleanup(struct cpudl *cp)
 212 {
 213         /*
 214          * nothing to do for the moment
 215          */
 216 }