xref: /openbmc/linux/block/blk-ioprio.c (revision ddf63516)
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  */
34 enum 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 
42 static 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 
50 static struct blkcg_policy ioprio_policy;
51 
52 /**
53  * struct ioprio_blkg - Per (cgroup, request queue) data.
54  * @pd: blkg_policy_data structure.
55  */
56 struct ioprio_blkg {
57 	struct blkg_policy_data pd;
58 };
59 
60 /**
61  * struct ioprio_blkcg - Per cgroup data.
62  * @cpd: blkcg_policy_data structure.
63  * @prio_policy: One of the IOPRIO_CLASS_* values. See also <linux/ioprio.h>.
64  */
65 struct ioprio_blkcg {
66 	struct blkcg_policy_data cpd;
67 	enum prio_policy	 prio_policy;
68 };
69 
pd_to_ioprio(struct blkg_policy_data * pd)70 static inline struct ioprio_blkg *pd_to_ioprio(struct blkg_policy_data *pd)
71 {
72 	return pd ? container_of(pd, struct ioprio_blkg, pd) : NULL;
73 }
74 
blkcg_to_ioprio_blkcg(struct blkcg * blkcg)75 static struct ioprio_blkcg *blkcg_to_ioprio_blkcg(struct blkcg *blkcg)
76 {
77 	return container_of(blkcg_to_cpd(blkcg, &ioprio_policy),
78 			    struct ioprio_blkcg, cpd);
79 }
80 
81 static struct ioprio_blkcg *
ioprio_blkcg_from_css(struct cgroup_subsys_state * css)82 ioprio_blkcg_from_css(struct cgroup_subsys_state *css)
83 {
84 	return blkcg_to_ioprio_blkcg(css_to_blkcg(css));
85 }
86 
ioprio_blkcg_from_bio(struct bio * bio)87 static struct ioprio_blkcg *ioprio_blkcg_from_bio(struct bio *bio)
88 {
89 	struct blkg_policy_data *pd = blkg_to_pd(bio->bi_blkg, &ioprio_policy);
90 
91 	if (!pd)
92 		return NULL;
93 
94 	return blkcg_to_ioprio_blkcg(pd->blkg->blkcg);
95 }
96 
ioprio_show_prio_policy(struct seq_file * sf,void * v)97 static int ioprio_show_prio_policy(struct seq_file *sf, void *v)
98 {
99 	struct ioprio_blkcg *blkcg = ioprio_blkcg_from_css(seq_css(sf));
100 
101 	seq_printf(sf, "%s\n", policy_name[blkcg->prio_policy]);
102 	return 0;
103 }
104 
ioprio_set_prio_policy(struct kernfs_open_file * of,char * buf,size_t nbytes,loff_t off)105 static ssize_t ioprio_set_prio_policy(struct kernfs_open_file *of, char *buf,
106 				      size_t nbytes, loff_t off)
107 {
108 	struct ioprio_blkcg *blkcg = ioprio_blkcg_from_css(of_css(of));
109 	int ret;
110 
111 	if (off != 0)
112 		return -EIO;
113 	/* kernfs_fop_write_iter() terminates 'buf' with '\0'. */
114 	ret = sysfs_match_string(policy_name, buf);
115 	if (ret < 0)
116 		return ret;
117 	blkcg->prio_policy = ret;
118 	return nbytes;
119 }
120 
121 static struct blkg_policy_data *
ioprio_alloc_pd(struct gendisk * disk,struct blkcg * blkcg,gfp_t gfp)122 ioprio_alloc_pd(struct gendisk *disk, struct blkcg *blkcg, gfp_t gfp)
123 {
124 	struct ioprio_blkg *ioprio_blkg;
125 
126 	ioprio_blkg = kzalloc(sizeof(*ioprio_blkg), gfp);
127 	if (!ioprio_blkg)
128 		return NULL;
129 
130 	return &ioprio_blkg->pd;
131 }
132 
ioprio_free_pd(struct blkg_policy_data * pd)133 static void ioprio_free_pd(struct blkg_policy_data *pd)
134 {
135 	struct ioprio_blkg *ioprio_blkg = pd_to_ioprio(pd);
136 
137 	kfree(ioprio_blkg);
138 }
139 
ioprio_alloc_cpd(gfp_t gfp)140 static struct blkcg_policy_data *ioprio_alloc_cpd(gfp_t gfp)
141 {
142 	struct ioprio_blkcg *blkcg;
143 
144 	blkcg = kzalloc(sizeof(*blkcg), gfp);
145 	if (!blkcg)
146 		return NULL;
147 	blkcg->prio_policy = POLICY_NO_CHANGE;
148 	return &blkcg->cpd;
149 }
150 
ioprio_free_cpd(struct blkcg_policy_data * cpd)151 static void ioprio_free_cpd(struct blkcg_policy_data *cpd)
152 {
153 	struct ioprio_blkcg *blkcg = container_of(cpd, typeof(*blkcg), cpd);
154 
155 	kfree(blkcg);
156 }
157 
158 #define IOPRIO_ATTRS						\
159 	{							\
160 		.name		= "prio.class",			\
161 		.seq_show	= ioprio_show_prio_policy,	\
162 		.write		= ioprio_set_prio_policy,	\
163 	},							\
164 	{ } /* sentinel */
165 
166 /* cgroup v2 attributes */
167 static struct cftype ioprio_files[] = {
168 	IOPRIO_ATTRS
169 };
170 
171 /* cgroup v1 attributes */
172 static struct cftype ioprio_legacy_files[] = {
173 	IOPRIO_ATTRS
174 };
175 
176 static struct blkcg_policy ioprio_policy = {
177 	.dfl_cftypes	= ioprio_files,
178 	.legacy_cftypes = ioprio_legacy_files,
179 
180 	.cpd_alloc_fn	= ioprio_alloc_cpd,
181 	.cpd_free_fn	= ioprio_free_cpd,
182 
183 	.pd_alloc_fn	= ioprio_alloc_pd,
184 	.pd_free_fn	= ioprio_free_pd,
185 };
186 
blkcg_set_ioprio(struct bio * bio)187 void blkcg_set_ioprio(struct bio *bio)
188 {
189 	struct ioprio_blkcg *blkcg = ioprio_blkcg_from_bio(bio);
190 	u16 prio;
191 
192 	if (!blkcg || blkcg->prio_policy == POLICY_NO_CHANGE)
193 		return;
194 
195 	if (blkcg->prio_policy == POLICY_PROMOTE_TO_RT ||
196 	    blkcg->prio_policy == POLICY_NONE_TO_RT) {
197 		/*
198 		 * For RT threads, the default priority level is 4 because
199 		 * task_nice is 0. By promoting non-RT io-priority to RT-class
200 		 * and default level 4, those requests that are already
201 		 * RT-class but need a higher io-priority can use ioprio_set()
202 		 * to achieve this.
203 		 */
204 		if (IOPRIO_PRIO_CLASS(bio->bi_ioprio) != IOPRIO_CLASS_RT)
205 			bio->bi_ioprio = IOPRIO_PRIO_VALUE(IOPRIO_CLASS_RT, 4);
206 		return;
207 	}
208 
209 	/*
210 	 * Except for IOPRIO_CLASS_NONE, higher I/O priority numbers
211 	 * correspond to a lower priority. Hence, the max_t() below selects
212 	 * the lower priority of bi_ioprio and the cgroup I/O priority class.
213 	 * If the bio I/O priority equals IOPRIO_CLASS_NONE, the cgroup I/O
214 	 * priority is assigned to the bio.
215 	 */
216 	prio = max_t(u16, bio->bi_ioprio,
217 			IOPRIO_PRIO_VALUE(blkcg->prio_policy, 0));
218 	if (prio > bio->bi_ioprio)
219 		bio->bi_ioprio = prio;
220 }
221 
blk_ioprio_exit(struct gendisk * disk)222 void blk_ioprio_exit(struct gendisk *disk)
223 {
224 	blkcg_deactivate_policy(disk, &ioprio_policy);
225 }
226 
blk_ioprio_init(struct gendisk * disk)227 int blk_ioprio_init(struct gendisk *disk)
228 {
229 	return blkcg_activate_policy(disk, &ioprio_policy);
230 }
231 
ioprio_init(void)232 static int __init ioprio_init(void)
233 {
234 	return blkcg_policy_register(&ioprio_policy);
235 }
236 
ioprio_exit(void)237 static void __exit ioprio_exit(void)
238 {
239 	blkcg_policy_unregister(&ioprio_policy);
240 }
241 
242 module_init(ioprio_init);
243 module_exit(ioprio_exit);
244