LXR linux/kernel/sched

   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
  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                cpumask_t *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                cpumask_t mask;
  78
  79                if (idx >= task_pri)
  80                        break;
  81
  82                cpus_and(mask, p->cpus_allowed, vec->mask);
  83
  84                if (cpus_empty(mask))
  85                        continue;
  86
  87                *lowest_mask = mask;
  88                return 1;
  89        }
  90
  91        return 0;
  92}
  93
  94/**
  95 * cpupri_set - update the cpu priority setting
  96 * @cp: The cpupri context
  97 * @cpu: The target cpu
  98 * @pri: The priority (INVALID-RT99) to assign to this CPU
  99 *
 100 * Note: Assumes cpu_rq(cpu)->lock is locked
 101 *
 102 * Returns: (void)
 103 */
 104void cpupri_set(struct cpupri *cp, int cpu, int newpri)
 105{
 106        int                 *currpri = &cp->cpu_to_pri[cpu];
 107        int                  oldpri  = *currpri;
 108        unsigned long        flags;
 109
 110        newpri = convert_prio(newpri);
 111
 112        BUG_ON(newpri >= CPUPRI_NR_PRIORITIES);
 113
 114        if (newpri == oldpri)
 115                return;
 116
 117        /*
 118         * If the cpu was currently mapped to a different value, we
 119         * first need to unmap the old value
 120         */
 121        if (likely(oldpri != CPUPRI_INVALID)) {
 122                struct cpupri_vec *vec  = &cp->pri_to_cpu[oldpri];
 123
 124                spin_lock_irqsave(&vec->lock, flags);
 125
 126                vec->count--;
 127                if (!vec->count)
 128                        clear_bit(oldpri, cp->pri_active);
 129                cpu_clear(cpu, vec->mask);
 130
 131                spin_unlock_irqrestore(&vec->lock, flags);
 132        }
 133
 134        if (likely(newpri != CPUPRI_INVALID)) {
 135                struct cpupri_vec *vec = &cp->pri_to_cpu[newpri];
 136
 137                spin_lock_irqsave(&vec->lock, flags);
 138
 139                cpu_set(cpu, vec->mask);
 140                vec->count++;
 141                if (vec->count == 1)
 142                        set_bit(newpri, cp->pri_active);
 143
 144                spin_unlock_irqrestore(&vec->lock, flags);
 145        }
 146
 147        *currpri = newpri;
 148}
 149
 150/**
 151 * cpupri_init - initialize the cpupri structure
 152 * @cp: The cpupri context
 153 *
 154 * Returns: (void)
 155 */
 156void cpupri_init(struct cpupri *cp)
 157{
 158        int i;
 159
 160        memset(cp, 0, sizeof(*cp));
 161
 162        for (i = 0; i < CPUPRI_NR_PRIORITIES; i++) {
 163                struct cpupri_vec *vec = &cp->pri_to_cpu[i];
 164
 165                spin_lock_init(&vec->lock);
 166                vec->count = 0;
 167                cpus_clear(vec->mask);
 168        }
 169
 170        for_each_possible_cpu(i)
 171                cp->cpu_to_pri[i] = CPUPRI_INVALID;
 172}
 173
 174
 175