linux/kernel/sched_cpupri.c
<<
>>
Prefs
   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 */
  33static 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 */
  69int 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                return 1;
  87        }
  88
  89        return 0;
  90}
  91
  92/**
  93 * cpupri_set - update the cpu priority setting
  94 * @cp: The cpupri context
  95 * @cpu: The target cpu
  96 * @pri: The priority (INVALID-RT99) to assign to this CPU
  97 *
  98 * Note: Assumes cpu_rq(cpu)->lock is locked
  99 *
 100 * Returns: (void)
 101 */
 102void cpupri_set(struct cpupri *cp, int cpu, int newpri)
 103{
 104        int                 *currpri = &cp->cpu_to_pri[cpu];
 105        int                  oldpri  = *currpri;
 106        unsigned long        flags;
 107
 108        newpri = convert_prio(newpri);
 109
 110        BUG_ON(newpri >= CPUPRI_NR_PRIORITIES);
 111
 112        if (newpri == oldpri)
 113                return;
 114
 115        /*
 116         * If the cpu was currently mapped to a different value, we
 117         * first need to unmap the old value
 118         */
 119        if (likely(oldpri != CPUPRI_INVALID)) {
 120                struct cpupri_vec *vec  = &cp->pri_to_cpu[oldpri];
 121
 122                spin_lock_irqsave(&vec->lock, flags);
 123
 124                vec->count--;
 125                if (!vec->count)
 126                        clear_bit(oldpri, cp->pri_active);
 127                cpumask_clear_cpu(cpu, vec->mask);
 128
 129                spin_unlock_irqrestore(&vec->lock, flags);
 130        }
 131
 132        if (likely(newpri != CPUPRI_INVALID)) {
 133                struct cpupri_vec *vec = &cp->pri_to_cpu[newpri];
 134
 135                spin_lock_irqsave(&vec->lock, flags);
 136
 137                cpumask_set_cpu(cpu, vec->mask);
 138                vec->count++;
 139                if (vec->count == 1)
 140                        set_bit(newpri, cp->pri_active);
 141
 142                spin_unlock_irqrestore(&vec->lock, flags);
 143        }
 144
 145        *currpri = newpri;
 146}
 147
 148/**
 149 * cpupri_init - initialize the cpupri structure
 150 * @cp: The cpupri context
 151 * @bootmem: true if allocations need to use bootmem
 152 *
 153 * Returns: -ENOMEM if memory fails.
 154 */
 155int __init_refok cpupri_init(struct cpupri *cp, bool bootmem)
 156{
 157        int i;
 158
 159        memset(cp, 0, sizeof(*cp));
 160
 161        for (i = 0; i < CPUPRI_NR_PRIORITIES; i++) {
 162                struct cpupri_vec *vec = &cp->pri_to_cpu[i];
 163
 164                spin_lock_init(&vec->lock);
 165                vec->count = 0;
 166                if (bootmem)
 167                        alloc_bootmem_cpumask_var(&vec->mask);
 168                else if (!zalloc_cpumask_var(&vec->mask, GFP_KERNEL))
 169                        goto cleanup;
 170        }
 171
 172        for_each_possible_cpu(i)
 173                cp->cpu_to_pri[i] = CPUPRI_INVALID;
 174        return 0;
 175
 176cleanup:
 177        for (i--; i >= 0; i--)
 178                free_cpumask_var(cp->pri_to_cpu[i].mask);
 179        return -ENOMEM;
 180}
 181
 182/**
 183 * cpupri_cleanup - clean up the cpupri structure
 184 * @cp: The cpupri context
 185 */
 186void cpupri_cleanup(struct cpupri *cp)
 187{
 188        int i;
 189
 190        for (i = 0; i < CPUPRI_NR_PRIORITIES; i++)
 191                free_cpumask_var(cp->pri_to_cpu[i].mask);
 192}
 193