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
17static 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
23static 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
34int blk_mq_update_queue_map(unsigned int *map, unsigned int nr_queues,
35			    const struct cpumask *online_mask)
36{
37	unsigned int i, nr_cpus, nr_uniq_cpus, queue, first_sibling;
38	cpumask_var_t cpus;
39
40	if (!alloc_cpumask_var(&cpus, GFP_ATOMIC))
41		return 1;
42
43	cpumask_clear(cpus);
44	nr_cpus = nr_uniq_cpus = 0;
45	for_each_cpu(i, online_mask) {
46		nr_cpus++;
47		first_sibling = get_first_sibling(i);
48		if (!cpumask_test_cpu(first_sibling, cpus))
49			nr_uniq_cpus++;
50		cpumask_set_cpu(i, cpus);
51	}
52
53	queue = 0;
54	for_each_possible_cpu(i) {
55		if (!cpumask_test_cpu(i, online_mask)) {
56			map[i] = 0;
57			continue;
58		}
59
60		/*
61		 * Easy case - we have equal or more hardware queues. Or
62		 * there are no thread siblings to take into account. Do
63		 * 1:1 if enough, or sequential mapping if less.
64		 */
65		if (nr_queues >= nr_cpus || nr_cpus == nr_uniq_cpus) {
66			map[i] = cpu_to_queue_index(nr_cpus, nr_queues, queue);
67			queue++;
68			continue;
69		}
70
71		/*
72		 * Less then nr_cpus queues, and we have some number of
73		 * threads per cores. Map sibling threads to the same
74		 * queue.
75		 */
76		first_sibling = get_first_sibling(i);
77		if (first_sibling == i) {
78			map[i] = cpu_to_queue_index(nr_uniq_cpus, nr_queues,
79							queue);
80			queue++;
81		} else
82			map[i] = map[first_sibling];
83	}
84
85	free_cpumask_var(cpus);
86	return 0;
87}
88
89unsigned int *blk_mq_make_queue_map(struct blk_mq_tag_set *set)
90{
91	unsigned int *map;
92
93	/* If cpus are offline, map them to first hctx */
94	map = kzalloc_node(sizeof(*map) * nr_cpu_ids, GFP_KERNEL,
95				set->numa_node);
96	if (!map)
97		return NULL;
98
99	if (!blk_mq_update_queue_map(map, set->nr_hw_queues, cpu_online_mask))
100		return map;
101
102	kfree(map);
103	return NULL;
104}
105
106/*
107 * We have no quick way of doing reverse lookups. This is only used at
108 * queue init time, so runtime isn't important.
109 */
110int blk_mq_hw_queue_to_node(unsigned int *mq_map, unsigned int index)
111{
112	int i;
113
114	for_each_possible_cpu(i) {
115		if (index == mq_map[i])
116			return cpu_to_node(i);
117	}
118
119	return NUMA_NO_NODE;
120}
121