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 <linux/gfp.h>
  31 #include "sched_cpupri.h"
  32
  33 /* Convert between a 140 based task->prio, and our 102 based cpupri */
  34 static int convert_prio(int prio)
  35 {
  36         int cpupri;
  37
  38         if (prio == CPUPRI_INVALID)
  39                 cpupri = CPUPRI_INVALID;
  40         else if (prio == MAX_PRIO)
  41                 cpupri = CPUPRI_IDLE;
  42         else if (prio >= MAX_RT_PRIO)
  43                 cpupri = CPUPRI_NORMAL;
  44         else
  45                 cpupri = MAX_RT_PRIO - prio + 1;
  46
  47         return cpupri;
  48 }
  49
  50 #define for_each_cpupri_active(array, idx)                    \
  51         for_each_set_bit(idx, array, CPUPRI_NR_PRIORITIES)
  52
  53 /**
  54  * cpupri_find - find the best (lowest-pri) CPU in the system
  55  * @cp: The cpupri context
  56  * @p: The task
  57  * @lowest_mask: A mask to fill in with selected CPUs (or NULL)
  58  *
  59  * Note: This function returns the recommended CPUs as calculated during the
  60  * current invocation.  By the time the call returns, the CPUs may have in
  61  * fact changed priorities any number of times.  While not ideal, it is not
  62  * an issue of correctness since the normal rebalancer logic will correct
  63  * any discrepancies created by racing against the uncertainty of the current
  64  * priority configuration.
  65  *
  66  * Returns: (int)bool - CPUs were found
  67  */
  68 int cpupri_find(struct cpupri *cp, struct task_struct *p,
  69                 struct cpumask *lowest_mask)
  70 {
  71         int                  idx      = 0;
  72         int                  task_pri = convert_prio(p->prio);
  73
  74         for_each_cpupri_active(cp->pri_active, idx) {
  75                 struct cpupri_vec *vec  = &cp->pri_to_cpu[idx];
  76
  77                 if (idx >= task_pri)
  78                         break;
  79
  80                 if (cpumask_any_and(&p->cpus_allowed, vec->mask) >= nr_cpu_ids)
  81                         continue;
  82
  83                 if (lowest_mask) {
  84                         cpumask_and(lowest_mask, &p->cpus_allowed, vec->mask);
  85
  86                         /*
  87                          * We have to ensure that we have at least one bit
  88                          * still set in the array, since the map could have
  89                          * been concurrently emptied between the first and
  90                          * second reads of vec->mask.  If we hit this
  91                          * condition, simply act as though we never hit this
  92                          * priority level and continue on.
  93                          */
  94                         if (cpumask_any(lowest_mask) >= nr_cpu_ids)
  95                                 continue;
  96                 }
  97
  98                 return 1;
  99         }
 100
 101         return 0;
 102 }
 103
 104 /**
 105  * cpupri_set - update the cpu priority setting
 106  * @cp: The cpupri context
 107  * @cpu: The target cpu
 108  * @pri: The priority (INVALID-RT99) to assign to this CPU
 109  *
 110  * Note: Assumes cpu_rq(cpu)->lock is locked
 111  *
 112  * Returns: (void)
 113  */
 114 void cpupri_set(struct cpupri *cp, int cpu, int newpri)
 115 {
 116         int                 *currpri = &cp->cpu_to_pri[cpu];
 117         int                  oldpri  = *currpri;
 118         unsigned long        flags;
 119
 120         newpri = convert_prio(newpri);
 121
 122         BUG_ON(newpri >= CPUPRI_NR_PRIORITIES);
 123
 124         if (newpri == oldpri)
 125                 return;
 126
 127         /*
 128          * If the cpu was currently mapped to a different value, we
 129          * need to map it to the new value then remove the old value.
 130          * Note, we must add the new value first, otherwise we risk the
 131          * cpu being cleared from pri_active, and this cpu could be
 132          * missed for a push or pull.
 133          */
 134         if (likely(newpri != CPUPRI_INVALID)) {
 135                 struct cpupri_vec *vec = &cp->pri_to_cpu[newpri];
 136
 137                 raw_spin_lock_irqsave(&vec->lock, flags);
 138
 139                 cpumask_set_cpu(cpu, vec->mask);
 140                 vec->count++;
 141                 if (vec->count == 1)
 142                         set_bit(newpri, cp->pri_active);
 143
 144                 raw_spin_unlock_irqrestore(&vec->lock, flags);
 145         }
 146         if (likely(oldpri != CPUPRI_INVALID)) {
 147                 struct cpupri_vec *vec  = &cp->pri_to_cpu[oldpri];
 148
 149                 raw_spin_lock_irqsave(&vec->lock, flags);
 150
 151                 vec->count--;
 152                 if (!vec->count)
 153                         clear_bit(oldpri, cp->pri_active);
 154                 cpumask_clear_cpu(cpu, vec->mask);
 155
 156                 raw_spin_unlock_irqrestore(&vec->lock, flags);
 157         }
 158
 159         *currpri = newpri;
 160 }
 161
 162 /**
 163  * cpupri_init - initialize the cpupri structure
 164  * @cp: The cpupri context
 165  * @bootmem: true if allocations need to use bootmem
 166  *
 167  * Returns: -ENOMEM if memory fails.
 168  */
 169 int cpupri_init(struct cpupri *cp)
 170 {
 171         int i;
 172
 173         memset(cp, 0, sizeof(*cp));
 174
 175         for (i = 0; i < CPUPRI_NR_PRIORITIES; i++) {
 176                 struct cpupri_vec *vec = &cp->pri_to_cpu[i];
 177
 178                 raw_spin_lock_init(&vec->lock);
 179                 vec->count = 0;
 180                 if (!zalloc_cpumask_var(&vec->mask, GFP_KERNEL))
 181                         goto cleanup;
 182         }
 183
 184         for_each_possible_cpu(i)
 185                 cp->cpu_to_pri[i] = CPUPRI_INVALID;
 186         return 0;
 187
 188 cleanup:
 189         for (i--; i >= 0; i--)
 190                 free_cpumask_var(cp->pri_to_cpu[i].mask);
 191         return -ENOMEM;
 192 }
 193
 194 /**
 195  * cpupri_cleanup - clean up the cpupri structure
 196  * @cp: The cpupri context
 197  */
 198 void cpupri_cleanup(struct cpupri *cp)
 199 {
 200         int i;
 201
 202         for (i = 0; i < CPUPRI_NR_PRIORITIES; i++)
 203                 free_cpumask_var(cp->pri_to_cpu[i].mask);
 204 }