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_update_queue_map(unsigned int *map, unsigned int nr_queues)
  35 {
  36         unsigned int i, nr_cpus, nr_uniq_cpus, queue, first_sibling;
  37         cpumask_var_t cpus;
  38
  39         if (!alloc_cpumask_var(&cpus, GFP_ATOMIC))
  40                 return 1;
  41
  42         cpumask_clear(cpus);
  43         nr_cpus = nr_uniq_cpus = 0;
  44         for_each_online_cpu(i) {
  45                 nr_cpus++;
  46                 first_sibling = get_first_sibling(i);
  47                 if (!cpumask_test_cpu(first_sibling, cpus))
  48                         nr_uniq_cpus++;
  49                 cpumask_set_cpu(i, cpus);
  50         }
  51
  52         queue = 0;
  53         for_each_possible_cpu(i) {
  54                 if (!cpu_online(i)) {
  55                         map[i] = 0;
  56                         continue;
  57                 }
  58
  59                 /*
  60                  * Easy case - we have equal or more hardware queues. Or
  61                  * there are no thread siblings to take into account. Do
  62                  * 1:1 if enough, or sequential mapping if less.
  63                  */
  64                 if (nr_queues >= nr_cpus || nr_cpus == nr_uniq_cpus) {
  65                         map[i] = cpu_to_queue_index(nr_cpus, nr_queues, queue);
  66                         queue++;
  67                         continue;
  68                 }
  69
  70                 /*
  71                  * Less then nr_cpus queues, and we have some number of
  72                  * threads per cores. Map sibling threads to the same
  73                  * queue.
  74                  */
  75                 first_sibling = get_first_sibling(i);
  76                 if (first_sibling == i) {
  77                         map[i] = cpu_to_queue_index(nr_uniq_cpus, nr_queues,
  78                                                         queue);
  79                         queue++;
  80                 } else
  81                         map[i] = map[first_sibling];
  82         }
  83
  84         free_cpumask_var(cpus);
  85         return 0;
  86 }
  87
  88 unsigned int *blk_mq_make_queue_map(struct blk_mq_tag_set *set)
  89 {
  90         unsigned int *map;
  91
  92         /* If cpus are offline, map them to first hctx */
  93         map = kzalloc_node(sizeof(*map) * nr_cpu_ids, GFP_KERNEL,
  94                                 set->numa_node);
  95         if (!map)
  96                 return NULL;
  97
  98         if (!blk_mq_update_queue_map(map, set->nr_hw_queues))
  99                 return map;
 100
 101         kfree(map);
 102         return NULL;
 103 }
 104
 105 /*
 106  * We have no quick way of doing reverse lookups. This is only used at
 107  * queue init time, so runtime isn't important.
 108  */
 109 int blk_mq_hw_queue_to_node(unsigned int *mq_map, unsigned int index)
 110 {
 111         int i;
 112
 113         for_each_possible_cpu(i) {
 114                 if (index == mq_map[i])
 115                         return cpu_to_node(i);
 116         }
 117
 118         return NUMA_NO_NODE;
 119 }