1/* 2 * Copyright (C) 2007-2009 NEC Corporation. All Rights Reserved. 3 * 4 * Module Author: Kiyoshi Ueda 5 * 6 * This file is released under the GPL. 7 * 8 * Throughput oriented path selector. 9 */ 10 11#include "dm.h" 12#include "dm-path-selector.h" 13 14#include <linux/slab.h> 15 16#define DM_MSG_PREFIX "multipath service-time" 17#define ST_MIN_IO 1 18#define ST_MAX_RELATIVE_THROUGHPUT 100 19#define ST_MAX_RELATIVE_THROUGHPUT_SHIFT 7 20#define ST_MAX_INFLIGHT_SIZE ((size_t)-1 >> ST_MAX_RELATIVE_THROUGHPUT_SHIFT) 21#define ST_VERSION "0.2.0" 22 23struct selector { 24 struct list_head valid_paths; 25 struct list_head failed_paths; 26}; 27 28struct path_info { 29 struct list_head list; 30 struct dm_path *path; 31 unsigned repeat_count; 32 unsigned relative_throughput; 33 atomic_t in_flight_size; /* Total size of in-flight I/Os */ 34}; 35 36static struct selector *alloc_selector(void) 37{ 38 struct selector *s = kmalloc(sizeof(*s), GFP_KERNEL); 39 40 if (s) { 41 INIT_LIST_HEAD(&s->valid_paths); 42 INIT_LIST_HEAD(&s->failed_paths); 43 } 44 45 return s; 46} 47 48static int st_create(struct path_selector *ps, unsigned argc, char **argv) 49{ 50 struct selector *s = alloc_selector(); 51 52 if (!s) 53 return -ENOMEM; 54 55 ps->context = s; 56 return 0; 57} 58 59static void free_paths(struct list_head *paths) 60{ 61 struct path_info *pi, *next; 62 63 list_for_each_entry_safe(pi, next, paths, list) { 64 list_del(&pi->list); 65 kfree(pi); 66 } 67} 68 69static void st_destroy(struct path_selector *ps) 70{ 71 struct selector *s = ps->context; 72 73 free_paths(&s->valid_paths); 74 free_paths(&s->failed_paths); 75 kfree(s); 76 ps->context = NULL; 77} 78 79static int st_status(struct path_selector *ps, struct dm_path *path, 80 status_type_t type, char *result, unsigned maxlen) 81{ 82 unsigned sz = 0; 83 struct path_info *pi; 84 85 if (!path) 86 DMEMIT("0 "); 87 else { 88 pi = path->pscontext; 89 90 switch (type) { 91 case STATUSTYPE_INFO: 92 DMEMIT("%d %u ", atomic_read(&pi->in_flight_size), 93 pi->relative_throughput); 94 break; 95 case STATUSTYPE_TABLE: 96 DMEMIT("%u %u ", pi->repeat_count, 97 pi->relative_throughput); 98 break; 99 } 100 } 101 102 return sz; 103} 104 105static int st_add_path(struct path_selector *ps, struct dm_path *path, 106 int argc, char **argv, char **error) 107{ 108 struct selector *s = ps->context; 109 struct path_info *pi; 110 unsigned repeat_count = ST_MIN_IO; 111 unsigned relative_throughput = 1; 112 113 /* 114 * Arguments: [<repeat_count> [<relative_throughput>]] 115 * <repeat_count>: The number of I/Os before switching path. 116 * If not given, default (ST_MIN_IO) is used. 117 * <relative_throughput>: The relative throughput value of 118 * the path among all paths in the path-group. 119 * The valid range: 0-<ST_MAX_RELATIVE_THROUGHPUT> 120 * If not given, minimum value '1' is used. 121 * If '0' is given, the path isn't selected while 122 * other paths having a positive value are 123 * available. 124 */ 125 if (argc > 2) { 126 *error = "service-time ps: incorrect number of arguments"; 127 return -EINVAL; 128 } 129 130 if (argc && (sscanf(argv[0], "%u", &repeat_count) != 1)) { 131 *error = "service-time ps: invalid repeat count"; 132 return -EINVAL; 133 } 134 135 if ((argc == 2) && 136 (sscanf(argv[1], "%u", &relative_throughput) != 1 || 137 relative_throughput > ST_MAX_RELATIVE_THROUGHPUT)) { 138 *error = "service-time ps: invalid relative_throughput value"; 139 return -EINVAL; 140 } 141 142 /* allocate the path */ 143 pi = kmalloc(sizeof(*pi), GFP_KERNEL); 144 if (!pi) { 145 *error = "service-time ps: Error allocating path context"; 146 return -ENOMEM; 147 } 148 149 pi->path = path; 150 pi->repeat_count = repeat_count; 151 pi->relative_throughput = relative_throughput; 152 atomic_set(&pi->in_flight_size, 0); 153 154 path->pscontext = pi; 155 156 list_add_tail(&pi->list, &s->valid_paths); 157 158 return 0; 159} 160 161static void st_fail_path(struct path_selector *ps, struct dm_path *path) 162{ 163 struct selector *s = ps->context; 164 struct path_info *pi = path->pscontext; 165 166 list_move(&pi->list, &s->failed_paths); 167} 168 169static int st_reinstate_path(struct path_selector *ps, struct dm_path *path) 170{ 171 struct selector *s = ps->context; 172 struct path_info *pi = path->pscontext; 173 174 list_move_tail(&pi->list, &s->valid_paths); 175 176 return 0; 177} 178 179/* 180 * Compare the estimated service time of 2 paths, pi1 and pi2, 181 * for the incoming I/O. 182 * 183 * Returns: 184 * < 0 : pi1 is better 185 * 0 : no difference between pi1 and pi2 186 * > 0 : pi2 is better 187 * 188 * Description: 189 * Basically, the service time is estimated by: 190 * ('pi->in-flight-size' + 'incoming') / 'pi->relative_throughput' 191 * To reduce the calculation, some optimizations are made. 192 * (See comments inline) 193 */ 194static int st_compare_load(struct path_info *pi1, struct path_info *pi2, 195 size_t incoming) 196{ 197 size_t sz1, sz2, st1, st2; 198 199 sz1 = atomic_read(&pi1->in_flight_size); 200 sz2 = atomic_read(&pi2->in_flight_size); 201 202 /* 203 * Case 1: Both have same throughput value. Choose less loaded path. 204 */ 205 if (pi1->relative_throughput == pi2->relative_throughput) 206 return sz1 - sz2; 207 208 /* 209 * Case 2a: Both have same load. Choose higher throughput path. 210 * Case 2b: One path has no throughput value. Choose the other one. 211 */ 212 if (sz1 == sz2 || 213 !pi1->relative_throughput || !pi2->relative_throughput) 214 return pi2->relative_throughput - pi1->relative_throughput; 215 216 /* 217 * Case 3: Calculate service time. Choose faster path. 218 * Service time using pi1: 219 * st1 = (sz1 + incoming) / pi1->relative_throughput 220 * Service time using pi2: 221 * st2 = (sz2 + incoming) / pi2->relative_throughput 222 * 223 * To avoid the division, transform the expression to use 224 * multiplication. 225 * Because ->relative_throughput > 0 here, if st1 < st2, 226 * the expressions below are the same meaning: 227 * (sz1 + incoming) / pi1->relative_throughput < 228 * (sz2 + incoming) / pi2->relative_throughput 229 * (sz1 + incoming) * pi2->relative_throughput < 230 * (sz2 + incoming) * pi1->relative_throughput 231 * So use the later one. 232 */ 233 sz1 += incoming; 234 sz2 += incoming; 235 if (unlikely(sz1 >= ST_MAX_INFLIGHT_SIZE || 236 sz2 >= ST_MAX_INFLIGHT_SIZE)) { 237 /* 238 * Size may be too big for multiplying pi->relative_throughput 239 * and overflow. 240 * To avoid the overflow and mis-selection, shift down both. 241 */ 242 sz1 >>= ST_MAX_RELATIVE_THROUGHPUT_SHIFT; 243 sz2 >>= ST_MAX_RELATIVE_THROUGHPUT_SHIFT; 244 } 245 st1 = sz1 * pi2->relative_throughput; 246 st2 = sz2 * pi1->relative_throughput; 247 if (st1 != st2) 248 return st1 - st2; 249 250 /* 251 * Case 4: Service time is equal. Choose higher throughput path. 252 */ 253 return pi2->relative_throughput - pi1->relative_throughput; 254} 255 256static struct dm_path *st_select_path(struct path_selector *ps, 257 unsigned *repeat_count, size_t nr_bytes) 258{ 259 struct selector *s = ps->context; 260 struct path_info *pi = NULL, *best = NULL; 261 262 if (list_empty(&s->valid_paths)) 263 return NULL; 264 265 /* Change preferred (first in list) path to evenly balance. */ 266 list_move_tail(s->valid_paths.next, &s->valid_paths); 267 268 list_for_each_entry(pi, &s->valid_paths, list) 269 if (!best || (st_compare_load(pi, best, nr_bytes) < 0)) 270 best = pi; 271 272 if (!best) 273 return NULL; 274 275 *repeat_count = best->repeat_count; 276 277 return best->path; 278} 279 280static int st_start_io(struct path_selector *ps, struct dm_path *path, 281 size_t nr_bytes) 282{ 283 struct path_info *pi = path->pscontext; 284 285 atomic_add(nr_bytes, &pi->in_flight_size); 286 287 return 0; 288} 289 290static int st_end_io(struct path_selector *ps, struct dm_path *path, 291 size_t nr_bytes) 292{ 293 struct path_info *pi = path->pscontext; 294 295 atomic_sub(nr_bytes, &pi->in_flight_size); 296 297 return 0; 298} 299 300static struct path_selector_type st_ps = { 301 .name = "service-time", 302 .module = THIS_MODULE, 303 .table_args = 2, 304 .info_args = 2, 305 .create = st_create, 306 .destroy = st_destroy, 307 .status = st_status, 308 .add_path = st_add_path, 309 .fail_path = st_fail_path, 310 .reinstate_path = st_reinstate_path, 311 .select_path = st_select_path, 312 .start_io = st_start_io, 313 .end_io = st_end_io, 314}; 315 316static int __init dm_st_init(void) 317{ 318 int r = dm_register_path_selector(&st_ps); 319 320 if (r < 0) 321 DMERR("register failed %d", r); 322 323 DMINFO("version " ST_VERSION " loaded"); 324 325 return r; 326} 327 328static void __exit dm_st_exit(void) 329{ 330 int r = dm_unregister_path_selector(&st_ps); 331 332 if (r < 0) 333 DMERR("unregister failed %d", r); 334} 335 336module_init(dm_st_init); 337module_exit(dm_st_exit); 338 339MODULE_DESCRIPTION(DM_NAME " throughput oriented path selector"); 340MODULE_AUTHOR("Kiyoshi Ueda <k-ueda@ct.jp.nec.com>"); 341MODULE_LICENSE("GPL"); 342