1 /* 2 * IPVS: Weighted Round-Robin Scheduling module 3 * 4 * Authors: Wensong Zhang <wensong@linuxvirtualserver.org> 5 * 6 * This program is free software; you can redistribute it and/or 7 * modify it under the terms of the GNU General Public License 8 * as published by the Free Software Foundation; either version 9 * 2 of the License, or (at your option) any later version. 10 * 11 * Changes: 12 * Wensong Zhang : changed the ip_vs_wrr_schedule to return dest 13 * Wensong Zhang : changed some comestics things for debugging 14 * Wensong Zhang : changed for the d-linked destination list 15 * Wensong Zhang : added the ip_vs_wrr_update_svc 16 * Julian Anastasov : fixed the bug of returning destination 17 * with weight 0 when all weights are zero 18 * 19 */ 20 21 #define KMSG_COMPONENT "IPVS" 22 #define pr_fmt(fmt) KMSG_COMPONENT ": " fmt 23 24 #include <linux/module.h> 25 #include <linux/kernel.h> 26 #include <linux/slab.h> 27 #include <linux/net.h> 28 #include <linux/gcd.h> 29 30 #include <net/ip_vs.h> 31 32 /* The WRR algorithm depends on some caclulations: 33 * - mw: maximum weight 34 * - di: weight step, greatest common divisor from all weights 35 * - cw: current required weight 36 * As result, all weights are in the [di..mw] range with a step=di. 37 * 38 * First, we start with cw = mw and select dests with weight >= cw. 39 * Then cw is reduced with di and all dests are checked again. 40 * Last pass should be with cw = di. We have mw/di passes in total: 41 * 42 * pass 1: cw = max weight 43 * pass 2: cw = max weight - di 44 * pass 3: cw = max weight - 2 * di 45 * ... 46 * last pass: cw = di 47 * 48 * Weights are supposed to be >= di but we run in parallel with 49 * weight changes, it is possible some dest weight to be reduced 50 * below di, bad if it is the only available dest. 51 * 52 * So, we modify how mw is calculated, now it is reduced with (di - 1), 53 * so that last cw is 1 to catch such dests with weight below di: 54 * pass 1: cw = max weight - (di - 1) 55 * pass 2: cw = max weight - di - (di - 1) 56 * pass 3: cw = max weight - 2 * di - (di - 1) 57 * ... 58 * last pass: cw = 1 59 * 60 */ 61 62 /* 63 * current destination pointer for weighted round-robin scheduling 64 */ 65 struct ip_vs_wrr_mark { 66 struct ip_vs_dest *cl; /* current dest or head */ 67 int cw; /* current weight */ 68 int mw; /* maximum weight */ 69 int di; /* decreasing interval */ 70 struct rcu_head rcu_head; 71 }; 72 73 74 static int ip_vs_wrr_gcd_weight(struct ip_vs_service *svc) 75 { 76 struct ip_vs_dest *dest; 77 int weight; 78 int g = 0; 79 80 list_for_each_entry(dest, &svc->destinations, n_list) { 81 weight = atomic_read(&dest->weight); 82 if (weight > 0) { 83 if (g > 0) 84 g = gcd(weight, g); 85 else 86 g = weight; 87 } 88 } 89 return g ? g : 1; 90 } 91 92 93 /* 94 * Get the maximum weight of the service destinations. 95 */ 96 static int ip_vs_wrr_max_weight(struct ip_vs_service *svc) 97 { 98 struct ip_vs_dest *dest; 99 int new_weight, weight = 0; 100 101 list_for_each_entry(dest, &svc->destinations, n_list) { 102 new_weight = atomic_read(&dest->weight); 103 if (new_weight > weight) 104 weight = new_weight; 105 } 106 107 return weight; 108 } 109 110 111 static int ip_vs_wrr_init_svc(struct ip_vs_service *svc) 112 { 113 struct ip_vs_wrr_mark *mark; 114 115 /* 116 * Allocate the mark variable for WRR scheduling 117 */ 118 mark = kmalloc(sizeof(struct ip_vs_wrr_mark), GFP_KERNEL); 119 if (mark == NULL) 120 return -ENOMEM; 121 122 mark->cl = list_entry(&svc->destinations, struct ip_vs_dest, n_list); 123 mark->di = ip_vs_wrr_gcd_weight(svc); 124 mark->mw = ip_vs_wrr_max_weight(svc) - (mark->di - 1); 125 mark->cw = mark->mw; 126 svc->sched_data = mark; 127 128 return 0; 129 } 130 131 132 static void ip_vs_wrr_done_svc(struct ip_vs_service *svc) 133 { 134 struct ip_vs_wrr_mark *mark = svc->sched_data; 135 136 /* 137 * Release the mark variable 138 */ 139 kfree_rcu(mark, rcu_head); 140 } 141 142 143 static int ip_vs_wrr_dest_changed(struct ip_vs_service *svc, 144 struct ip_vs_dest *dest) 145 { 146 struct ip_vs_wrr_mark *mark = svc->sched_data; 147 148 spin_lock_bh(&svc->sched_lock); 149 mark->cl = list_entry(&svc->destinations, struct ip_vs_dest, n_list); 150 mark->di = ip_vs_wrr_gcd_weight(svc); 151 mark->mw = ip_vs_wrr_max_weight(svc) - (mark->di - 1); 152 if (mark->cw > mark->mw || !mark->cw) 153 mark->cw = mark->mw; 154 else if (mark->di > 1) 155 mark->cw = (mark->cw / mark->di) * mark->di + 1; 156 spin_unlock_bh(&svc->sched_lock); 157 return 0; 158 } 159 160 161 /* 162 * Weighted Round-Robin Scheduling 163 */ 164 static struct ip_vs_dest * 165 ip_vs_wrr_schedule(struct ip_vs_service *svc, const struct sk_buff *skb, 166 struct ip_vs_iphdr *iph) 167 { 168 struct ip_vs_dest *dest, *last, *stop = NULL; 169 struct ip_vs_wrr_mark *mark = svc->sched_data; 170 bool last_pass = false, restarted = false; 171 172 IP_VS_DBG(6, "%s(): Scheduling...\n", __func__); 173 174 spin_lock_bh(&svc->sched_lock); 175 dest = mark->cl; 176 /* No available dests? */ 177 if (mark->mw == 0) 178 goto err_noavail; 179 last = dest; 180 /* Stop only after all dests were checked for weight >= 1 (last pass) */ 181 while (1) { 182 list_for_each_entry_continue_rcu(dest, 183 &svc->destinations, 184 n_list) { 185 if (!(dest->flags & IP_VS_DEST_F_OVERLOAD) && 186 atomic_read(&dest->weight) >= mark->cw) 187 goto found; 188 if (dest == stop) 189 goto err_over; 190 } 191 mark->cw -= mark->di; 192 if (mark->cw <= 0) { 193 mark->cw = mark->mw; 194 /* Stop if we tried last pass from first dest: 195 * 1. last_pass: we started checks when cw > di but 196 * then all dests were checked for w >= 1 197 * 2. last was head: the first and only traversal 198 * was for weight >= 1, for all dests. 199 */ 200 if (last_pass || 201 &last->n_list == &svc->destinations) 202 goto err_over; 203 restarted = true; 204 } 205 last_pass = mark->cw <= mark->di; 206 if (last_pass && restarted && 207 &last->n_list != &svc->destinations) { 208 /* First traversal was for w >= 1 but only 209 * for dests after 'last', now do the same 210 * for all dests up to 'last'. 211 */ 212 stop = last; 213 } 214 } 215 216 found: 217 IP_VS_DBG_BUF(6, "WRR: server %s:%u " 218 "activeconns %d refcnt %d weight %d\n", 219 IP_VS_DBG_ADDR(dest->af, &dest->addr), ntohs(dest->port), 220 atomic_read(&dest->activeconns), 221 refcount_read(&dest->refcnt), 222 atomic_read(&dest->weight)); 223 mark->cl = dest; 224 225 out: 226 spin_unlock_bh(&svc->sched_lock); 227 return dest; 228 229 err_noavail: 230 mark->cl = dest; 231 dest = NULL; 232 ip_vs_scheduler_err(svc, "no destination available"); 233 goto out; 234 235 err_over: 236 mark->cl = dest; 237 dest = NULL; 238 ip_vs_scheduler_err(svc, "no destination available: " 239 "all destinations are overloaded"); 240 goto out; 241 } 242 243 244 static struct ip_vs_scheduler ip_vs_wrr_scheduler = { 245 .name = "wrr", 246 .refcnt = ATOMIC_INIT(0), 247 .module = THIS_MODULE, 248 .n_list = LIST_HEAD_INIT(ip_vs_wrr_scheduler.n_list), 249 .init_service = ip_vs_wrr_init_svc, 250 .done_service = ip_vs_wrr_done_svc, 251 .add_dest = ip_vs_wrr_dest_changed, 252 .del_dest = ip_vs_wrr_dest_changed, 253 .upd_dest = ip_vs_wrr_dest_changed, 254 .schedule = ip_vs_wrr_schedule, 255 }; 256 257 static int __init ip_vs_wrr_init(void) 258 { 259 return register_ip_vs_scheduler(&ip_vs_wrr_scheduler) ; 260 } 261 262 static void __exit ip_vs_wrr_cleanup(void) 263 { 264 unregister_ip_vs_scheduler(&ip_vs_wrr_scheduler); 265 synchronize_rcu(); 266 } 267 268 module_init(ip_vs_wrr_init); 269 module_exit(ip_vs_wrr_cleanup); 270 MODULE_LICENSE("GPL"); 271