1// SPDX-License-Identifier: GPL-2.0
2/*
3 * Block rq-qos policy for assigning an I/O priority class to requests.
4 *
5 * Using an rq-qos policy for assigning I/O priority class has two advantages
6 * over using the ioprio_set() system call:
7 *
8 * - This policy is cgroup based so it has all the advantages of cgroups.
9 * - While ioprio_set() does not affect page cache writeback I/O, this rq-qos
10 * controller affects page cache writeback I/O for filesystems that support
11 * assiociating a cgroup with writeback I/O. See also
12 * Documentation/admin-guide/cgroup-v2.rst.
13 */
14
15#include <linux/blk-mq.h>
16#include <linux/blk_types.h>
17#include <linux/kernel.h>
18#include <linux/module.h>
19#include "blk-cgroup.h"
20#include "blk-ioprio.h"
21#include "blk-rq-qos.h"
22
23/**
24 * enum prio_policy - I/O priority class policy.
25 * @POLICY_NO_CHANGE: (default) do not modify the I/O priority class.
26 * @POLICY_PROMOTE_TO_RT: modify no-IOPRIO_CLASS_RT to IOPRIO_CLASS_RT.
27 * @POLICY_RESTRICT_TO_BE: modify IOPRIO_CLASS_NONE and IOPRIO_CLASS_RT into
28 * IOPRIO_CLASS_BE.
29 * @POLICY_ALL_TO_IDLE: change the I/O priority class into IOPRIO_CLASS_IDLE.
30 * @POLICY_NONE_TO_RT: an alias for POLICY_PROMOTE_TO_RT.
31 *
32 * See also <linux/ioprio.h>.
33 */
34enum prio_policy {
35 POLICY_NO_CHANGE = 0,
36 POLICY_PROMOTE_TO_RT = 1,
37 POLICY_RESTRICT_TO_BE = 2,
38 POLICY_ALL_TO_IDLE = 3,
39 POLICY_NONE_TO_RT = 4,
40};
41
42static const char *policy_name[] = {
43 [POLICY_NO_CHANGE] = "no-change",
44 [POLICY_PROMOTE_TO_RT] = "promote-to-rt",
45 [POLICY_RESTRICT_TO_BE] = "restrict-to-be",
46 [POLICY_ALL_TO_IDLE] = "idle",
47 [POLICY_NONE_TO_RT] = "none-to-rt",
48};
49
50static struct blkcg_policy ioprio_policy;
51
52/**
53 * struct ioprio_blkcg - Per cgroup data.
54 * @cpd: blkcg_policy_data structure.
55 * @prio_policy: One of the IOPRIO_CLASS_* values. See also <linux/ioprio.h>.
56 */
57struct ioprio_blkcg {
58 struct blkcg_policy_data cpd;
59 enum prio_policy prio_policy;
60};
61
62static struct ioprio_blkcg *blkcg_to_ioprio_blkcg(struct blkcg *blkcg)
63{
64 return container_of(blkcg_to_cpd(blkcg, &ioprio_policy),
65 struct ioprio_blkcg, cpd);
66}
67
68static struct ioprio_blkcg *
69ioprio_blkcg_from_css(struct cgroup_subsys_state *css)
70{
71 return blkcg_to_ioprio_blkcg(blkcg: css_to_blkcg(css));
72}
73
74static int ioprio_show_prio_policy(struct seq_file *sf, void *v)
75{
76 struct ioprio_blkcg *blkcg = ioprio_blkcg_from_css(css: seq_css(seq: sf));
77
78 seq_printf(m: sf, fmt: "%s\n", policy_name[blkcg->prio_policy]);
79 return 0;
80}
81
82static ssize_t ioprio_set_prio_policy(struct kernfs_open_file *of, char *buf,
83 size_t nbytes, loff_t off)
84{
85 struct ioprio_blkcg *blkcg = ioprio_blkcg_from_css(css: of_css(of));
86 int ret;
87
88 if (off != 0)
89 return -EIO;
90 /* kernfs_fop_write_iter() terminates 'buf' with '\0'. */
91 ret = sysfs_match_string(policy_name, buf);
92 if (ret < 0)
93 return ret;
94 blkcg->prio_policy = ret;
95 return nbytes;
96}
97
98static struct blkcg_policy_data *ioprio_alloc_cpd(gfp_t gfp)
99{
100 struct ioprio_blkcg *blkcg;
101
102 blkcg = kzalloc(sizeof(*blkcg), gfp);
103 if (!blkcg)
104 return NULL;
105 blkcg->prio_policy = POLICY_NO_CHANGE;
106 return &blkcg->cpd;
107}
108
109static void ioprio_free_cpd(struct blkcg_policy_data *cpd)
110{
111 struct ioprio_blkcg *blkcg = container_of(cpd, typeof(*blkcg), cpd);
112
113 kfree(objp: blkcg);
114}
115
116static struct cftype ioprio_files[] = {
117 {
118 .name = "prio.class",
119 .seq_show = ioprio_show_prio_policy,
120 .write = ioprio_set_prio_policy,
121 },
122 { } /* sentinel */
123};
124
125static struct blkcg_policy ioprio_policy = {
126 .dfl_cftypes = ioprio_files,
127 .legacy_cftypes = ioprio_files,
128
129 .cpd_alloc_fn = ioprio_alloc_cpd,
130 .cpd_free_fn = ioprio_free_cpd,
131};
132
133void blkcg_set_ioprio(struct bio *bio)
134{
135 struct ioprio_blkcg *blkcg = blkcg_to_ioprio_blkcg(blkcg: bio->bi_blkg->blkcg);
136 u16 prio;
137
138 if (!blkcg || blkcg->prio_policy == POLICY_NO_CHANGE)
139 return;
140
141 if (blkcg->prio_policy == POLICY_PROMOTE_TO_RT ||
142 blkcg->prio_policy == POLICY_NONE_TO_RT) {
143 /*
144 * For RT threads, the default priority level is 4 because
145 * task_nice is 0. By promoting non-RT io-priority to RT-class
146 * and default level 4, those requests that are already
147 * RT-class but need a higher io-priority can use ioprio_set()
148 * to achieve this.
149 */
150 if (IOPRIO_PRIO_CLASS(bio->bi_ioprio) != IOPRIO_CLASS_RT)
151 bio->bi_ioprio = IOPRIO_PRIO_VALUE(IOPRIO_CLASS_RT, 4);
152 return;
153 }
154
155 /*
156 * Except for IOPRIO_CLASS_NONE, higher I/O priority numbers
157 * correspond to a lower priority. Hence, the max_t() below selects
158 * the lower priority of bi_ioprio and the cgroup I/O priority class.
159 * If the bio I/O priority equals IOPRIO_CLASS_NONE, the cgroup I/O
160 * priority is assigned to the bio.
161 */
162 prio = max_t(u16, bio->bi_ioprio,
163 IOPRIO_PRIO_VALUE(blkcg->prio_policy, 0));
164 if (prio > bio->bi_ioprio)
165 bio->bi_ioprio = prio;
166}
167
168static int __init ioprio_init(void)
169{
170 return blkcg_policy_register(pol: &ioprio_policy);
171}
172
173static void __exit ioprio_exit(void)
174{
175 blkcg_policy_unregister(pol: &ioprio_policy);
176}
177
178module_init(ioprio_init);
179module_exit(ioprio_exit);
180