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                 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  */
 104 void 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  */
 156 void 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