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 <asm/atomic.h> 24 25#define DM_MSG_PREFIX "multipath queue-length" 26#define QL_MIN_IO 128 27#define QL_VERSION "0.1.0" 28 29struct selector { 30 struct list_head valid_paths; 31 struct list_head failed_paths; 32}; 33 34struct path_info { 35 struct list_head list; 36 struct dm_path *path; 37 unsigned repeat_count; 38 atomic_t qlen; /* the number of in-flight I/Os */ 39}; 40 41static struct selector *alloc_selector(void) 42{ 43 struct selector *s = kmalloc(sizeof(*s), GFP_KERNEL); 44 45 if (s) { 46 INIT_LIST_HEAD(&s->valid_paths); 47 INIT_LIST_HEAD(&s->failed_paths); 48 } 49 50 return s; 51} 52 53static int ql_create(struct path_selector *ps, unsigned argc, char **argv) 54{ 55 struct selector *s = alloc_selector(); 56 57 if (!s) 58 return -ENOMEM; 59 60 ps->context = s; 61 return 0; 62} 63 64static void ql_free_paths(struct list_head *paths) 65{ 66 struct path_info *pi, *next; 67 68 list_for_each_entry_safe(pi, next, paths, list) { 69 list_del(&pi->list); 70 kfree(pi); 71 } 72} 73 74static void ql_destroy(struct path_selector *ps) 75{ 76 struct selector *s = ps->context; 77 78 ql_free_paths(&s->valid_paths); 79 ql_free_paths(&s->failed_paths); 80 kfree(s); 81 ps->context = NULL; 82} 83 84static int ql_status(struct path_selector *ps, struct dm_path *path, 85 status_type_t type, char *result, unsigned maxlen) 86{ 87 unsigned sz = 0; 88 struct path_info *pi; 89 90 /* When called with NULL path, return selector status/args. */ 91 if (!path) 92 DMEMIT("0 "); 93 else { 94 pi = path->pscontext; 95 96 switch (type) { 97 case STATUSTYPE_INFO: 98 DMEMIT("%d ", atomic_read(&pi->qlen)); 99 break; 100 case STATUSTYPE_TABLE: 101 DMEMIT("%u ", pi->repeat_count); 102 break; 103 } 104 } 105 106 return sz; 107} 108 109static int ql_add_path(struct path_selector *ps, struct dm_path *path, 110 int argc, char **argv, char **error) 111{ 112 struct selector *s = ps->context; 113 struct path_info *pi; 114 unsigned repeat_count = QL_MIN_IO; 115 116 /* 117 * Arguments: [<repeat_count>] 118 * <repeat_count>: The number of I/Os before switching path. 119 * If not given, default (QL_MIN_IO) is used. 120 */ 121 if (argc > 1) { 122 *error = "queue-length ps: incorrect number of arguments"; 123 return -EINVAL; 124 } 125 126 if ((argc == 1) && (sscanf(argv[0], "%u", &repeat_count) != 1)) { 127 *error = "queue-length ps: invalid repeat count"; 128 return -EINVAL; 129 } 130 131 /* Allocate the path information structure */ 132 pi = kmalloc(sizeof(*pi), GFP_KERNEL); 133 if (!pi) { 134 *error = "queue-length ps: Error allocating path information"; 135 return -ENOMEM; 136 } 137 138 pi->path = path; 139 pi->repeat_count = repeat_count; 140 atomic_set(&pi->qlen, 0); 141 142 path->pscontext = pi; 143 144 list_add_tail(&pi->list, &s->valid_paths); 145 146 return 0; 147} 148 149static void ql_fail_path(struct path_selector *ps, struct dm_path *path) 150{ 151 struct selector *s = ps->context; 152 struct path_info *pi = path->pscontext; 153 154 list_move(&pi->list, &s->failed_paths); 155} 156 157static int ql_reinstate_path(struct path_selector *ps, struct dm_path *path) 158{ 159 struct selector *s = ps->context; 160 struct path_info *pi = path->pscontext; 161 162 list_move_tail(&pi->list, &s->valid_paths); 163 164 return 0; 165} 166 167/* 168 * Select a path having the minimum number of in-flight I/Os 169 */ 170static struct dm_path *ql_select_path(struct path_selector *ps, 171 unsigned *repeat_count, size_t nr_bytes) 172{ 173 struct selector *s = ps->context; 174 struct path_info *pi = NULL, *best = NULL; 175 176 if (list_empty(&s->valid_paths)) 177 return NULL; 178 179 /* Change preferred (first in list) path to evenly balance. */ 180 list_move_tail(s->valid_paths.next, &s->valid_paths); 181 182 list_for_each_entry(pi, &s->valid_paths, list) { 183 if (!best || 184 (atomic_read(&pi->qlen) < atomic_read(&best->qlen))) 185 best = pi; 186 187 if (!atomic_read(&best->qlen)) 188 break; 189 } 190 191 if (!best) 192 return NULL; 193 194 *repeat_count = best->repeat_count; 195 196 return best->path; 197} 198 199static int ql_start_io(struct path_selector *ps, struct dm_path *path, 200 size_t nr_bytes) 201{ 202 struct path_info *pi = path->pscontext; 203 204 atomic_inc(&pi->qlen); 205 206 return 0; 207} 208 209static int ql_end_io(struct path_selector *ps, struct dm_path *path, 210 size_t nr_bytes) 211{ 212 struct path_info *pi = path->pscontext; 213 214 atomic_dec(&pi->qlen); 215 216 return 0; 217} 218 219static struct path_selector_type ql_ps = { 220 .name = "queue-length", 221 .module = THIS_MODULE, 222 .table_args = 1, 223 .info_args = 1, 224 .create = ql_create, 225 .destroy = ql_destroy, 226 .status = ql_status, 227 .add_path = ql_add_path, 228 .fail_path = ql_fail_path, 229 .reinstate_path = ql_reinstate_path, 230 .select_path = ql_select_path, 231 .start_io = ql_start_io, 232 .end_io = ql_end_io, 233}; 234 235static int __init dm_ql_init(void) 236{ 237 int r = dm_register_path_selector(&ql_ps); 238 239 if (r < 0) 240 DMERR("register failed %d", r); 241 242 DMINFO("version " QL_VERSION " loaded"); 243 244 return r; 245} 246 247static void __exit dm_ql_exit(void) 248{ 249 int r = dm_unregister_path_selector(&ql_ps); 250 251 if (r < 0) 252 DMERR("unregister failed %d", r); 253} 254 255module_init(dm_ql_init); 256module_exit(dm_ql_exit); 257 258MODULE_AUTHOR("Stefan Bader <Stefan.Bader at de.ibm.com>"); 259MODULE_DESCRIPTION( 260 "(C) Copyright IBM Corp. 2004,2005 All Rights Reserved.\n" 261 DM_NAME " path selector to balance the number of in-flight I/Os" 262); 263MODULE_LICENSE("GPL"); 264