1 /* 2 * Copyright (C) 2004-2005 IBM Corp. All Rights Reserved. 3 * Copyright (C) 2006-2009 NEC Corporation. 4 * 5 * dm-queue-length.c 6 * 7 * Module Author: Stefan Bader, IBM 8 * Modified by: Kiyoshi Ueda, NEC 9 * 10 * This file is released under the GPL. 11 * 12 * queue-length path selector - choose a path with the least number of 13 * in-flight I/Os. 14 */ 15 16 #include "dm.h" 17 #include "dm-path-selector.h" 18 19 #include <linux/slab.h> 20 #include <linux/ctype.h> 21 #include <linux/errno.h> 22 #include <linux/module.h> 23 #include <linux/atomic.h> 24 25 #define DM_MSG_PREFIX "multipath queue-length" 26 #define QL_MIN_IO 1 27 #define QL_VERSION "0.2.0" 28 29 struct selector { 30 struct list_head valid_paths; 31 struct list_head failed_paths; 32 spinlock_t lock; 33 }; 34 35 struct path_info { 36 struct list_head list; 37 struct dm_path *path; 38 unsigned repeat_count; 39 atomic_t qlen; /* the number of in-flight I/Os */ 40 }; 41 42 static struct selector *alloc_selector(void) 43 { 44 struct selector *s = kmalloc(sizeof(*s), GFP_KERNEL); 45 46 if (s) { 47 INIT_LIST_HEAD(&s->valid_paths); 48 INIT_LIST_HEAD(&s->failed_paths); 49 spin_lock_init(&s->lock); 50 } 51 52 return s; 53 } 54 55 static int ql_create(struct path_selector *ps, unsigned argc, char **argv) 56 { 57 struct selector *s = alloc_selector(); 58 59 if (!s) 60 return -ENOMEM; 61 62 ps->context = s; 63 return 0; 64 } 65 66 static void ql_free_paths(struct list_head *paths) 67 { 68 struct path_info *pi, *next; 69 70 list_for_each_entry_safe(pi, next, paths, list) { 71 list_del(&pi->list); 72 kfree(pi); 73 } 74 } 75 76 static void ql_destroy(struct path_selector *ps) 77 { 78 struct selector *s = ps->context; 79 80 ql_free_paths(&s->valid_paths); 81 ql_free_paths(&s->failed_paths); 82 kfree(s); 83 ps->context = NULL; 84 } 85 86 static int ql_status(struct path_selector *ps, struct dm_path *path, 87 status_type_t type, char *result, unsigned maxlen) 88 { 89 unsigned sz = 0; 90 struct path_info *pi; 91 92 /* When called with NULL path, return selector status/args. */ 93 if (!path) 94 DMEMIT("0 "); 95 else { 96 pi = path->pscontext; 97 98 switch (type) { 99 case STATUSTYPE_INFO: 100 DMEMIT("%d ", atomic_read(&pi->qlen)); 101 break; 102 case STATUSTYPE_TABLE: 103 DMEMIT("%u ", pi->repeat_count); 104 break; 105 } 106 } 107 108 return sz; 109 } 110 111 static int ql_add_path(struct path_selector *ps, struct dm_path *path, 112 int argc, char **argv, char **error) 113 { 114 struct selector *s = ps->context; 115 struct path_info *pi; 116 unsigned repeat_count = QL_MIN_IO; 117 char dummy; 118 unsigned long flags; 119 120 /* 121 * Arguments: [<repeat_count>] 122 * <repeat_count>: The number of I/Os before switching path. 123 * If not given, default (QL_MIN_IO) is used. 124 */ 125 if (argc > 1) { 126 *error = "queue-length ps: incorrect number of arguments"; 127 return -EINVAL; 128 } 129 130 if ((argc == 1) && (sscanf(argv[0], "%u%c", &repeat_count, &dummy) != 1)) { 131 *error = "queue-length ps: invalid repeat count"; 132 return -EINVAL; 133 } 134 135 if (repeat_count > 1) { 136 DMWARN_LIMIT("repeat_count > 1 is deprecated, using 1 instead"); 137 repeat_count = 1; 138 } 139 140 /* Allocate the path information structure */ 141 pi = kmalloc(sizeof(*pi), GFP_KERNEL); 142 if (!pi) { 143 *error = "queue-length ps: Error allocating path information"; 144 return -ENOMEM; 145 } 146 147 pi->path = path; 148 pi->repeat_count = repeat_count; 149 atomic_set(&pi->qlen, 0); 150 151 path->pscontext = pi; 152 153 spin_lock_irqsave(&s->lock, flags); 154 list_add_tail(&pi->list, &s->valid_paths); 155 spin_unlock_irqrestore(&s->lock, flags); 156 157 return 0; 158 } 159 160 static void ql_fail_path(struct path_selector *ps, struct dm_path *path) 161 { 162 struct selector *s = ps->context; 163 struct path_info *pi = path->pscontext; 164 unsigned long flags; 165 166 spin_lock_irqsave(&s->lock, flags); 167 list_move(&pi->list, &s->failed_paths); 168 spin_unlock_irqrestore(&s->lock, flags); 169 } 170 171 static int ql_reinstate_path(struct path_selector *ps, struct dm_path *path) 172 { 173 struct selector *s = ps->context; 174 struct path_info *pi = path->pscontext; 175 unsigned long flags; 176 177 spin_lock_irqsave(&s->lock, flags); 178 list_move_tail(&pi->list, &s->valid_paths); 179 spin_unlock_irqrestore(&s->lock, flags); 180 181 return 0; 182 } 183 184 /* 185 * Select a path having the minimum number of in-flight I/Os 186 */ 187 static struct dm_path *ql_select_path(struct path_selector *ps, size_t nr_bytes) 188 { 189 struct selector *s = ps->context; 190 struct path_info *pi = NULL, *best = NULL; 191 struct dm_path *ret = NULL; 192 unsigned long flags; 193 194 spin_lock_irqsave(&s->lock, flags); 195 if (list_empty(&s->valid_paths)) 196 goto out; 197 198 list_for_each_entry(pi, &s->valid_paths, list) { 199 if (!best || 200 (atomic_read(&pi->qlen) < atomic_read(&best->qlen))) 201 best = pi; 202 203 if (!atomic_read(&best->qlen)) 204 break; 205 } 206 207 if (!best) 208 goto out; 209 210 /* Move most recently used to least preferred to evenly balance. */ 211 list_move_tail(&best->list, &s->valid_paths); 212 213 ret = best->path; 214 out: 215 spin_unlock_irqrestore(&s->lock, flags); 216 return ret; 217 } 218 219 static int ql_start_io(struct path_selector *ps, struct dm_path *path, 220 size_t nr_bytes) 221 { 222 struct path_info *pi = path->pscontext; 223 224 atomic_inc(&pi->qlen); 225 226 return 0; 227 } 228 229 static int ql_end_io(struct path_selector *ps, struct dm_path *path, 230 size_t nr_bytes, u64 start_time) 231 { 232 struct path_info *pi = path->pscontext; 233 234 atomic_dec(&pi->qlen); 235 236 return 0; 237 } 238 239 static struct path_selector_type ql_ps = { 240 .name = "queue-length", 241 .module = THIS_MODULE, 242 .table_args = 1, 243 .info_args = 1, 244 .create = ql_create, 245 .destroy = ql_destroy, 246 .status = ql_status, 247 .add_path = ql_add_path, 248 .fail_path = ql_fail_path, 249 .reinstate_path = ql_reinstate_path, 250 .select_path = ql_select_path, 251 .start_io = ql_start_io, 252 .end_io = ql_end_io, 253 }; 254 255 static int __init dm_ql_init(void) 256 { 257 int r = dm_register_path_selector(&ql_ps); 258 259 if (r < 0) 260 DMERR("register failed %d", r); 261 262 DMINFO("version " QL_VERSION " loaded"); 263 264 return r; 265 } 266 267 static void __exit dm_ql_exit(void) 268 { 269 int r = dm_unregister_path_selector(&ql_ps); 270 271 if (r < 0) 272 DMERR("unregister failed %d", r); 273 } 274 275 module_init(dm_ql_init); 276 module_exit(dm_ql_exit); 277 278 MODULE_AUTHOR("Stefan Bader <Stefan.Bader at de.ibm.com>"); 279 MODULE_DESCRIPTION( 280 "(C) Copyright IBM Corp. 2004,2005 All Rights Reserved.\n" 281 DM_NAME " path selector to balance the number of in-flight I/Os" 282 ); 283 MODULE_LICENSE("GPL"); 284