block/blk-mq-cpumap.c

   1 /*
   2  * CPU <-> hardware queue mapping helpers
   3  *
   4  * Copyright (C) 2013-2014 Jens Axboe
   5  */
   6 #include <linux/kernel.h>
   7 #include <linux/threads.h>
   8 #include <linux/module.h>
   9 #include <linux/mm.h>
  10 #include <linux/smp.h>
  11 #include <linux/cpu.h>
  12
  13 #include <linux/blk-mq.h>
  14 #include "blk.h"
  15 #include "blk-mq.h"
  16
  17 static int cpu_to_queue_index(unsigned int nr_cpus, unsigned int nr_queues,
  18                               const int cpu)
  19 {
  20         return cpu * nr_queues / nr_cpus;
  21 }
  22
  23 static int get_first_sibling(unsigned int cpu)
  24 {
  25         unsigned int ret;
  26
  27         ret = cpumask_first(topology_sibling_cpumask(cpu));
  28         if (ret < nr_cpu_ids)
  29                 return ret;
  30
  31         return cpu;
  32 }
  33
  34 int blk_mq_map_queues(struct blk_mq_tag_set *set)
  35 {
  36         unsigned int *map = set->mq_map;
  37         unsigned int nr_queues = set->nr_hw_queues;
  38         const struct cpumask *online_mask = cpu_online_mask;
  39         unsigned int i, nr_cpus, nr_uniq_cpus, queue, first_sibling;
  40         cpumask_var_t cpus;
  41
  42         if (!alloc_cpumask_var(&cpus, GFP_ATOMIC))
  43                 return -ENOMEM;
  44
  45         cpumask_clear(cpus);
  46         nr_cpus = nr_uniq_cpus = 0;
  47         for_each_cpu(i, online_mask) {
  48                 nr_cpus++;
  49                 first_sibling = get_first_sibling(i);
  50                 if (!cpumask_test_cpu(first_sibling, cpus))
  51                         nr_uniq_cpus++;
  52                 cpumask_set_cpu(i, cpus);
  53         }
  54
  55         queue = 0;
  56         for_each_possible_cpu(i) {
  57                 if (!cpumask_test_cpu(i, online_mask)) {
  58                         map[i] = 0;
  59                         continue;
  60                 }
  61
  62                 /*
  63                  * Easy case - we have equal or more hardware queues. Or
  64                  * there are no thread siblings to take into account. Do
  65                  * 1:1 if enough, or sequential mapping if less.
  66                  */
  67                 if (nr_queues >= nr_cpus || nr_cpus == nr_uniq_cpus) {
  68                         map[i] = cpu_to_queue_index(nr_cpus, nr_queues, queue);
  69                         queue++;
  70                         continue;
  71                 }
  72
  73                 /*
  74                  * Less then nr_cpus queues, and we have some number of
  75                  * threads per cores. Map sibling threads to the same
  76                  * queue.
  77                  */
  78                 first_sibling = get_first_sibling(i);
  79                 if (first_sibling == i) {
  80                         map[i] = cpu_to_queue_index(nr_uniq_cpus, nr_queues,
  81                                                         queue);
  82                         queue++;
  83                 } else
  84                         map[i] = map[first_sibling];
  85         }
  86
  87         free_cpumask_var(cpus);
  88         return 0;
  89 }
  90
  91 /*
  92  * We have no quick way of doing reverse lookups. This is only used at
  93  * queue init time, so runtime isn't important.
  94  */
  95 int blk_mq_hw_queue_to_node(unsigned int *mq_map, unsigned int index)
  96 {
  97         int i;
  98
  99         for_each_possible_cpu(i) {
 100                 if (index == mq_map[i])
 101                         return local_memory_node(cpu_to_node(i));
 102         }
 103
 104         return NUMA_NO_NODE;
 105 }