kernel/sched_cpupri.c

   1 /*
   2  *  kernel/sched_cpupri.c
   3  *
   4  *  CPU priority management
   5  *
   6  *  Copyright (C) 2007-2008 Novell
   7  *
   8  *  Author: Gregory Haskins <ghaskins@novell.com>
   9  *
  10  *  This code tracks the priority of each CPU so that global migration
  11  *  decisions are easy to calculate.  Each CPU can be in a state as follows:
  12  *
  13  *                 (INVALID), IDLE, NORMAL, RT1, ... RT99
  14  *
  15  *  going from the lowest priority to the highest.  CPUs in the INVALID state
  16  *  are not eligible for routing.  The system maintains this state with
  17  *  a 2 dimensional bitmap (the first for priority class, the second for cpus
  18  *  in that class).  Therefore a typical application without affinity
  19  *  restrictions can find a suitable CPU with O(1) complexity (e.g. two bit
  20  *  searches).  For tasks with affinity restrictions, the algorithm has a
  21  *  worst case complexity of O(min(102, nr_domcpus)), though the scenario that
  22  *  yields the worst case search is fairly contrived.
  23  *
  24  *  This program is free software; you can redistribute it and/or
  25  *  modify it under the terms of the GNU General Public License
  26  *  as published by the Free Software Foundation; version 2
  27  *  of the License.
  28  */
  29
  30 #include "sched_cpupri.h"
  31
  32 /* Convert between a 140 based task->prio, and our 102 based cpupri */
  33 static int convert_prio(int prio)
  34 {
  35         int cpupri;
  36
  37         if (prio == CPUPRI_INVALID)
  38                 cpupri = CPUPRI_INVALID;
  39         else if (prio == MAX_PRIO)
  40                 cpupri = CPUPRI_IDLE;
  41         else if (prio >= MAX_RT_PRIO)
  42                 cpupri = CPUPRI_NORMAL;
  43         else
  44                 cpupri = MAX_RT_PRIO - prio + 1;
  45
  46         return cpupri;
  47 }
  48
  49 #define for_each_cpupri_active(array, idx)                    \
  50   for (idx = find_first_bit(array, CPUPRI_NR_PRIORITIES);     \
  51        idx < CPUPRI_NR_PRIORITIES;                            \
  52        idx = find_next_bit(array, CPUPRI_NR_PRIORITIES, idx+1))
  53
  54 /**
  55  * cpupri_find - find the best (lowest-pri) CPU in the system
  56  * @cp: The cpupri context
  57  * @p: The task
  58  * @lowest_mask: A mask to fill in with selected CPUs (or NULL)
  59  *
  60  * Note: This function returns the recommended CPUs as calculated during the
  61  * current invokation.  By the time the call returns, the CPUs may have in
  62  * fact changed priorities any number of times.  While not ideal, it is not
  63  * an issue of correctness since the normal rebalancer logic will correct
  64  * any discrepancies created by racing against the uncertainty of the current
  65  * priority configuration.
  66  *
  67  * Returns: (int)bool - CPUs were found
  68  */
  69 int cpupri_find(struct cpupri *cp, struct task_struct *p,
  70                 struct cpumask *lowest_mask)
  71 {
  72         int                  idx      = 0;
  73         int                  task_pri = convert_prio(p->prio);
  74
  75         for_each_cpupri_active(cp->pri_active, idx) {
  76                 struct cpupri_vec *vec  = &cp->pri_to_cpu[idx];
  77
  78                 if (idx >= task_pri)
  79                         break;
  80
  81                 if (cpumask_any_and(&p->cpus_allowed, vec->mask) >= nr_cpu_ids)
  82                         continue;
  83
  84                 if (lowest_mask) {
  85                         cpumask_and(lowest_mask, &p->cpus_allowed, vec->mask);
  86
  87                         /*
  88                          * We have to ensure that we have at least one bit
  89                          * still set in the array, since the map could have
  90                          * been concurrently emptied between the first and
  91                          * second reads of vec->mask.  If we hit this
  92                          * condition, simply act as though we never hit this
  93                          * priority level and continue on.
  94                          */
  95                         if (cpumask_any(lowest_mask) >= nr_cpu_ids)
  96                                 continue;
  97                 }
  98
  99                 return 1;
 100         }
 101
 102         return 0;
 103 }
 104
 105 /**
 106  * cpupri_set - update the cpu priority setting
 107  * @cp: The cpupri context
 108  * @cpu: The target cpu
 109  * @pri: The priority (INVALID-RT99) to assign to this CPU
 110  *
 111  * Note: Assumes cpu_rq(cpu)->lock is locked
 112  *
 113  * Returns: (void)
 114  */
 115 void cpupri_set(struct cpupri *cp, int cpu, int newpri)
 116 {
 117         int                 *currpri = &cp->cpu_to_pri[cpu];
 118         int                  oldpri  = *currpri;
 119         unsigned long        flags;
 120
 121         newpri = convert_prio(newpri);
 122
 123         BUG_ON(newpri >= CPUPRI_NR_PRIORITIES);
 124
 125         if (newpri == oldpri)
 126                 return;
 127
 128         /*
 129          * If the cpu was currently mapped to a different value, we
 130          * need to map it to the new value then remove the old value.
 131          * Note, we must add the new value first, otherwise we risk the
 132          * cpu being cleared from pri_active, and this cpu could be
 133          * missed for a push or pull.
 134          */
 135         if (likely(newpri != CPUPRI_INVALID)) {
 136                 struct cpupri_vec *vec = &cp->pri_to_cpu[newpri];
 137
 138                 spin_lock_irqsave(&vec->lock, flags);
 139
 140                 cpumask_set_cpu(cpu, vec->mask);
 141                 vec->count++;
 142                 if (vec->count == 1)
 143                         set_bit(newpri, cp->pri_active);
 144
 145                 spin_unlock_irqrestore(&vec->lock, flags);
 146         }
 147         if (likely(oldpri != CPUPRI_INVALID)) {
 148                 struct cpupri_vec *vec  = &cp->pri_to_cpu[oldpri];
 149
 150                 spin_lock_irqsave(&vec->lock, flags);
 151
 152                 vec->count--;
 153                 if (!vec->count)
 154                         clear_bit(oldpri, cp->pri_active);
 155                 cpumask_clear_cpu(cpu, vec->mask);
 156
 157                 spin_unlock_irqrestore(&vec->lock, flags);
 158         }
 159
 160         *currpri = newpri;
 161 }
 162
 163 /**
 164  * cpupri_init - initialize the cpupri structure
 165  * @cp: The cpupri context
 166  * @bootmem: true if allocations need to use bootmem
 167  *
 168  * Returns: -ENOMEM if memory fails.
 169  */
 170 int cpupri_init(struct cpupri *cp, bool bootmem)
 171 {
 172         gfp_t gfp = GFP_KERNEL;
 173         int i;
 174
 175         if (bootmem)
 176                 gfp = GFP_NOWAIT;
 177
 178         memset(cp, 0, sizeof(*cp));
 179
 180         for (i = 0; i < CPUPRI_NR_PRIORITIES; i++) {
 181                 struct cpupri_vec *vec = &cp->pri_to_cpu[i];
 182
 183                 spin_lock_init(&vec->lock);
 184                 vec->count = 0;
 185                 if (!zalloc_cpumask_var(&vec->mask, gfp))
 186                         goto cleanup;
 187         }
 188
 189         for_each_possible_cpu(i)
 190                 cp->cpu_to_pri[i] = CPUPRI_INVALID;
 191         return 0;
 192
 193 cleanup:
 194         for (i--; i >= 0; i--)
 195                 free_cpumask_var(cp->pri_to_cpu[i].mask);
 196         return -ENOMEM;
 197 }
 198
 199 /**
 200  * cpupri_cleanup - clean up the cpupri structure
 201  * @cp: The cpupri context
 202  */
 203 void cpupri_cleanup(struct cpupri *cp)
 204 {
 205         int i;
 206
 207         for (i = 0; i < CPUPRI_NR_PRIORITIES; i++)
 208                 free_cpumask_var(cp->pri_to_cpu[i].mask);
 209 }