linux/kernel/sched_cpupri.c
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   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 */
  34static 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 */
  68int 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 */
 114void 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 */
 169int 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
 188cleanup:
 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 */
 198void 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}
 205
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