FreeBSD/Linux Kernel Cross Reference
sys/kernel/sched_cpupri.c

     /*
      *  kernel/sched_cpupri.c
      *
      *  CPU priority management
      *
      *  Copyright (C) 2007-2008 Novell
      *
      *  Author: Gregory Haskins <ghaskins@novell.com>
      *
     *  This code tracks the priority of each CPU so that global migration
     *  decisions are easy to calculate.  Each CPU can be in a state as follows:
     *
     *                 (INVALID), IDLE, NORMAL, RT1, ... RT99
     *
     *  going from the lowest priority to the highest.  CPUs in the INVALID state
     *  are not eligible for routing.  The system maintains this state with
     *  a 2 dimensional bitmap (the first for priority class, the second for cpus
     *  in that class).  Therefore a typical application without affinity
     *  restrictions can find a suitable CPU with O(1) complexity (e.g. two bit
     *  searches).  For tasks with affinity restrictions, the algorithm has a
     *  worst case complexity of O(min(102, nr_domcpus)), though the scenario that
     *  yields the worst case search is fairly contrived.
     *
     *  This program is free software; you can redistribute it and/or
     *  modify it under the terms of the GNU General Public License
     *  as published by the Free Software Foundation; version 2
     *  of the License.
     */
    
    #include <linux/gfp.h>
    #include "sched_cpupri.h"
    
    /* Convert between a 140 based task->prio, and our 102 based cpupri */
    static int convert_prio(int prio)
    {
            int cpupri;
    
            if (prio == CPUPRI_INVALID)
                    cpupri = CPUPRI_INVALID;
            else if (prio == MAX_PRIO)
                    cpupri = CPUPRI_IDLE;
            else if (prio >= MAX_RT_PRIO)
                    cpupri = CPUPRI_NORMAL;
            else
                    cpupri = MAX_RT_PRIO - prio + 1;
    
            return cpupri;
    }
    
    #define for_each_cpupri_active(array, idx)                    \
            for_each_set_bit(idx, array, CPUPRI_NR_PRIORITIES)
    
    /**
     * cpupri_find - find the best (lowest-pri) CPU in the system
     * @cp: The cpupri context
     * @p: The task
     * @lowest_mask: A mask to fill in with selected CPUs (or NULL)
     *
     * Note: This function returns the recommended CPUs as calculated during the
     * current invocation.  By the time the call returns, the CPUs may have in
     * fact changed priorities any number of times.  While not ideal, it is not
     * an issue of correctness since the normal rebalancer logic will correct
     * any discrepancies created by racing against the uncertainty of the current
     * priority configuration.
     *
     * Returns: (int)bool - CPUs were found
     */
    int cpupri_find(struct cpupri *cp, struct task_struct *p,
                    struct cpumask *lowest_mask)
    {
            int                  idx      = 0;
            int                  task_pri = convert_prio(p->prio);
    
            for_each_cpupri_active(cp->pri_active, idx) {
                    struct cpupri_vec *vec  = &cp->pri_to_cpu[idx];
    
                    if (idx >= task_pri)
                            break;
    
                    if (cpumask_any_and(&p->cpus_allowed, vec->mask) >= nr_cpu_ids)
                            continue;
    
                    if (lowest_mask) {
                            cpumask_and(lowest_mask, &p->cpus_allowed, vec->mask);
    
                            /*
                             * We have to ensure that we have at least one bit
                             * still set in the array, since the map could have
                             * been concurrently emptied between the first and
                             * second reads of vec->mask.  If we hit this
                             * condition, simply act as though we never hit this
                             * priority level and continue on.
                             */
                            if (cpumask_any(lowest_mask) >= nr_cpu_ids)
                                    continue;
                    }
    
                    return 1;
            }
   
           return 0;
   }
   
   /**
    * cpupri_set - update the cpu priority setting
    * @cp: The cpupri context
    * @cpu: The target cpu
    * @pri: The priority (INVALID-RT99) to assign to this CPU
    *
    * Note: Assumes cpu_rq(cpu)->lock is locked
    *
    * Returns: (void)
    */
   void cpupri_set(struct cpupri *cp, int cpu, int newpri)
   {
           int                 *currpri = &cp->cpu_to_pri[cpu];
           int                  oldpri  = *currpri;
           unsigned long        flags;
   
           newpri = convert_prio(newpri);
   
           BUG_ON(newpri >= CPUPRI_NR_PRIORITIES);
   
           if (newpri == oldpri)
                   return;
   
           /*
            * If the cpu was currently mapped to a different value, we
            * need to map it to the new value then remove the old value.
            * Note, we must add the new value first, otherwise we risk the
            * cpu being cleared from pri_active, and this cpu could be
            * missed for a push or pull.
            */
           if (likely(newpri != CPUPRI_INVALID)) {
                   struct cpupri_vec *vec = &cp->pri_to_cpu[newpri];
   
                   raw_spin_lock_irqsave(&vec->lock, flags);
   
                   cpumask_set_cpu(cpu, vec->mask);
                   vec->count++;
                   if (vec->count == 1)
                           set_bit(newpri, cp->pri_active);
   
                   raw_spin_unlock_irqrestore(&vec->lock, flags);
           }
           if (likely(oldpri != CPUPRI_INVALID)) {
                   struct cpupri_vec *vec  = &cp->pri_to_cpu[oldpri];
   
                   raw_spin_lock_irqsave(&vec->lock, flags);
   
                   vec->count--;
                   if (!vec->count)
                           clear_bit(oldpri, cp->pri_active);
                   cpumask_clear_cpu(cpu, vec->mask);
   
                   raw_spin_unlock_irqrestore(&vec->lock, flags);
           }
   
           *currpri = newpri;
   }
   
   /**
    * cpupri_init - initialize the cpupri structure
    * @cp: The cpupri context
    * @bootmem: true if allocations need to use bootmem
    *
    * Returns: -ENOMEM if memory fails.
    */
   int cpupri_init(struct cpupri *cp)
   {
           int i;
   
           memset(cp, 0, sizeof(*cp));
   
           for (i = 0; i < CPUPRI_NR_PRIORITIES; i++) {
                   struct cpupri_vec *vec = &cp->pri_to_cpu[i];
   
                   raw_spin_lock_init(&vec->lock);
                   vec->count = 0;
                   if (!zalloc_cpumask_var(&vec->mask, GFP_KERNEL))
                           goto cleanup;
           }
   
           for_each_possible_cpu(i)
                   cp->cpu_to_pri[i] = CPUPRI_INVALID;
           return 0;
   
   cleanup:
           for (i--; i >= 0; i--)
                   free_cpumask_var(cp->pri_to_cpu[i].mask);
           return -ENOMEM;
   }
   
   /**
    * cpupri_cleanup - clean up the cpupri structure
    * @cp: The cpupri context
    */
   void cpupri_cleanup(struct cpupri *cp)
   {
           int i;
   
           for (i = 0; i < CPUPRI_NR_PRIORITIES; i++)
                   free_cpumask_var(cp->pri_to_cpu[i].mask);
   }

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