1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * CPU <-> hardware queue mapping helpers
4  *
5  * Copyright (C) 2013-2014 Jens Axboe
6  */
7 #include <linux/kernel.h>
8 #include <linux/threads.h>
9 #include <linux/module.h>
10 #include <linux/mm.h>
11 #include <linux/smp.h>
12 #include <linux/cpu.h>
13 
14 #include <linux/blk-mq.h>
15 #include "blk.h"
16 #include "blk-mq.h"
17 
queue_index(struct blk_mq_queue_map * qmap,unsigned int nr_queues,const int q)18 static int queue_index(struct blk_mq_queue_map *qmap,
19 		       unsigned int nr_queues, const int q)
20 {
21 	return qmap->queue_offset + (q % nr_queues);
22 }
23 
get_first_sibling(unsigned int cpu)24 static int get_first_sibling(unsigned int cpu)
25 {
26 	unsigned int ret;
27 
28 	ret = cpumask_first(topology_sibling_cpumask(cpu));
29 	if (ret < nr_cpu_ids)
30 		return ret;
31 
32 	return cpu;
33 }
34 
blk_mq_map_queues(struct blk_mq_queue_map * qmap)35 int blk_mq_map_queues(struct blk_mq_queue_map *qmap)
36 {
37 	unsigned int *map = qmap->mq_map;
38 	unsigned int nr_queues = qmap->nr_queues;
39 	unsigned int cpu, first_sibling, q = 0;
40 
41 	for_each_possible_cpu(cpu)
42 		map[cpu] = -1;
43 
44 	/*
45 	 * Spread queues among present CPUs first for minimizing
46 	 * count of dead queues which are mapped by all un-present CPUs
47 	 */
48 	for_each_present_cpu(cpu) {
49 		if (q >= nr_queues)
50 			break;
51 		map[cpu] = queue_index(qmap, nr_queues, q++);
52 	}
53 
54 	for_each_possible_cpu(cpu) {
55 		if (map[cpu] != -1)
56 			continue;
57 		/*
58 		 * First do sequential mapping between CPUs and queues.
59 		 * In case we still have CPUs to map, and we have some number of
60 		 * threads per cores then map sibling threads to the same queue
61 		 * for performance optimizations.
62 		 */
63 		if (q < nr_queues) {
64 			map[cpu] = queue_index(qmap, nr_queues, q++);
65 		} else {
66 			first_sibling = get_first_sibling(cpu);
67 			if (first_sibling == cpu)
68 				map[cpu] = queue_index(qmap, nr_queues, q++);
69 			else
70 				map[cpu] = map[first_sibling];
71 		}
72 	}
73 
74 	return 0;
75 }
76 EXPORT_SYMBOL_GPL(blk_mq_map_queues);
77 
78 /**
79  * blk_mq_hw_queue_to_node - Look up the memory node for a hardware queue index
80  * @qmap: CPU to hardware queue map.
81  * @index: hardware queue index.
82  *
83  * We have no quick way of doing reverse lookups. This is only used at
84  * queue init time, so runtime isn't important.
85  */
blk_mq_hw_queue_to_node(struct blk_mq_queue_map * qmap,unsigned int index)86 int blk_mq_hw_queue_to_node(struct blk_mq_queue_map *qmap, unsigned int index)
87 {
88 	int i;
89 
90 	for_each_possible_cpu(i) {
91 		if (index == qmap->mq_map[i])
92 			return cpu_to_node(i);
93 	}
94 
95 	return NUMA_NO_NODE;
96 }
97