net/netfilter/ipvs/ip_vs_wrr.c

   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 {
 167         struct ip_vs_dest *dest, *last, *stop = NULL;
 168         struct ip_vs_wrr_mark *mark = svc->sched_data;
 169         bool last_pass = false, restarted = false;
 170
 171         IP_VS_DBG(6, "%s(): Scheduling...\n", __func__);
 172
 173         spin_lock_bh(&svc->sched_lock);
 174         dest = mark->cl;
 175         /* No available dests? */
 176         if (mark->mw == 0)
 177                 goto err_noavail;
 178         last = dest;
 179         /* Stop only after all dests were checked for weight >= 1 (last pass) */
 180         while (1) {
 181                 list_for_each_entry_continue_rcu(dest,
 182                                                  &svc->destinations,
 183                                                  n_list) {
 184                         if (!(dest->flags & IP_VS_DEST_F_OVERLOAD) &&
 185                             atomic_read(&dest->weight) >= mark->cw)
 186                                 goto found;
 187                         if (dest == stop)
 188                                 goto err_over;
 189                 }
 190                 mark->cw -= mark->di;
 191                 if (mark->cw <= 0) {
 192                         mark->cw = mark->mw;
 193                         /* Stop if we tried last pass from first dest:
 194                          * 1. last_pass: we started checks when cw > di but
 195                          *      then all dests were checked for w >= 1
 196                          * 2. last was head: the first and only traversal
 197                          *      was for weight >= 1, for all dests.
 198                          */
 199                         if (last_pass ||
 200                             &last->n_list == &svc->destinations)
 201                                 goto err_over;
 202                         restarted = true;
 203                 }
 204                 last_pass = mark->cw <= mark->di;
 205                 if (last_pass && restarted &&
 206                     &last->n_list != &svc->destinations) {
 207                         /* First traversal was for w >= 1 but only
 208                          * for dests after 'last', now do the same
 209                          * for all dests up to 'last'.
 210                          */
 211                         stop = last;
 212                 }
 213         }
 214
 215 found:
 216         IP_VS_DBG_BUF(6, "WRR: server %s:%u "
 217                       "activeconns %d refcnt %d weight %d\n",
 218                       IP_VS_DBG_ADDR(svc->af, &dest->addr), ntohs(dest->port),
 219                       atomic_read(&dest->activeconns),
 220                       atomic_read(&dest->refcnt),
 221                       atomic_read(&dest->weight));
 222         mark->cl = dest;
 223
 224   out:
 225         spin_unlock_bh(&svc->sched_lock);
 226         return dest;
 227
 228 err_noavail:
 229         mark->cl = dest;
 230         dest = NULL;
 231         ip_vs_scheduler_err(svc, "no destination available");
 232         goto out;
 233
 234 err_over:
 235         mark->cl = dest;
 236         dest = NULL;
 237         ip_vs_scheduler_err(svc, "no destination available: "
 238                             "all destinations are overloaded");
 239         goto out;
 240 }
 241
 242
 243 static struct ip_vs_scheduler ip_vs_wrr_scheduler = {
 244         .name =                 "wrr",
 245         .refcnt =               ATOMIC_INIT(0),
 246         .module =               THIS_MODULE,
 247         .n_list =               LIST_HEAD_INIT(ip_vs_wrr_scheduler.n_list),
 248         .init_service =         ip_vs_wrr_init_svc,
 249         .done_service =         ip_vs_wrr_done_svc,
 250         .add_dest =             ip_vs_wrr_dest_changed,
 251         .del_dest =             ip_vs_wrr_dest_changed,
 252         .upd_dest =             ip_vs_wrr_dest_changed,
 253         .schedule =             ip_vs_wrr_schedule,
 254 };
 255
 256 static int __init ip_vs_wrr_init(void)
 257 {
 258         return register_ip_vs_scheduler(&ip_vs_wrr_scheduler) ;
 259 }
 260
 261 static void __exit ip_vs_wrr_cleanup(void)
 262 {
 263         unregister_ip_vs_scheduler(&ip_vs_wrr_scheduler);
 264         synchronize_rcu();
 265 }
 266
 267 module_init(ip_vs_wrr_init);
 268 module_exit(ip_vs_wrr_cleanup);
 269 MODULE_LICENSE("GPL");