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
  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                 cpumask_and(lowest_mask, &p->cpus_allowed, vec->mask);
  85                 return 1;
  86         }
  87
  88         return 0;
  89 }
  90
  91 /**
  92  * cpupri_set - update the cpu priority setting
  93  * @cp: The cpupri context
  94  * @cpu: The target cpu
  95  * @pri: The priority (INVALID-RT99) to assign to this CPU
  96  *
  97  * Note: Assumes cpu_rq(cpu)->lock is locked
  98  *
  99  * Returns: (void)
 100  */
 101 void cpupri_set(struct cpupri *cp, int cpu, int newpri)
 102 {
 103         int                 *currpri = &cp->cpu_to_pri[cpu];
 104         int                  oldpri  = *currpri;
 105         unsigned long        flags;
 106
 107         newpri = convert_prio(newpri);
 108
 109         BUG_ON(newpri >= CPUPRI_NR_PRIORITIES);
 110
 111         if (newpri == oldpri)
 112                 return;
 113
 114         /*
 115          * If the cpu was currently mapped to a different value, we
 116          * first need to unmap the old value
 117          */
 118         if (likely(oldpri != CPUPRI_INVALID)) {
 119                 struct cpupri_vec *vec  = &cp->pri_to_cpu[oldpri];
 120
 121                 spin_lock_irqsave(&vec->lock, flags);
 122
 123                 vec->count--;
 124                 if (!vec->count)
 125                         clear_bit(oldpri, cp->pri_active);
 126                 cpumask_clear_cpu(cpu, vec->mask);
 127
 128                 spin_unlock_irqrestore(&vec->lock, flags);
 129         }
 130
 131         if (likely(newpri != CPUPRI_INVALID)) {
 132                 struct cpupri_vec *vec = &cp->pri_to_cpu[newpri];
 133
 134                 spin_lock_irqsave(&vec->lock, flags);
 135
 136                 cpumask_set_cpu(cpu, vec->mask);
 137                 vec->count++;
 138                 if (vec->count == 1)
 139                         set_bit(newpri, cp->pri_active);
 140
 141                 spin_unlock_irqrestore(&vec->lock, flags);
 142         }
 143
 144         *currpri = newpri;
 145 }
 146
 147 /**
 148  * cpupri_init - initialize the cpupri structure
 149  * @cp: The cpupri context
 150  * @bootmem: true if allocations need to use bootmem
 151  *
 152  * Returns: -ENOMEM if memory fails.
 153  */
 154 int __init_refok cpupri_init(struct cpupri *cp, bool bootmem)
 155 {
 156         int i;
 157
 158         memset(cp, 0, sizeof(*cp));
 159
 160         for (i = 0; i < CPUPRI_NR_PRIORITIES; i++) {
 161                 struct cpupri_vec *vec = &cp->pri_to_cpu[i];
 162
 163                 spin_lock_init(&vec->lock);
 164                 vec->count = 0;
 165                 if (bootmem)
 166                         alloc_bootmem_cpumask_var(&vec->mask);
 167                 else if (!alloc_cpumask_var(&vec->mask, GFP_KERNEL))
 168                         goto cleanup;
 169         }
 170
 171         for_each_possible_cpu(i)
 172                 cp->cpu_to_pri[i] = CPUPRI_INVALID;
 173         return 0;
 174
 175 cleanup:
 176         for (i--; i >= 0; i--)
 177                 free_cpumask_var(cp->pri_to_cpu[i].mask);
 178         return -ENOMEM;
 179 }
 180
 181 /**
 182  * cpupri_cleanup - clean up the cpupri structure
 183  * @cp: The cpupri context
 184  */
 185 void cpupri_cleanup(struct cpupri *cp)
 186 {
 187         int i;
 188
 189         for (i = 0; i < CPUPRI_NR_PRIORITIES; i++)
 190                 free_cpumask_var(cp->pri_to_cpu[i].mask);
 191 }