1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /*
3 * IPVS: Weighted Round-Robin Scheduling module
4 *
5 * Authors: Wensong Zhang <wensong@linuxvirtualserver.org>
6 *
7 * Changes:
8 * Wensong Zhang : changed the ip_vs_wrr_schedule to return dest
9 * Wensong Zhang : changed some comestics things for debugging
10 * Wensong Zhang : changed for the d-linked destination list
11 * Wensong Zhang : added the ip_vs_wrr_update_svc
12 * Julian Anastasov : fixed the bug of returning destination
13 * with weight 0 when all weights are zero
14 */
15
16 #define pr_fmt(fmt) "IPVS: " fmt
17
18 #include <linux/module.h>
19 #include <linux/kernel.h>
20 #include <linux/slab.h>
21 #include <linux/net.h>
22 #include <linux/gcd.h>
23
24 #include <net/ip_vs.h>
25
26 /* The WRR algorithm depends on some caclulations:
27 * - mw: maximum weight
28 * - di: weight step, greatest common divisor from all weights
29 * - cw: current required weight
30 * As result, all weights are in the [di..mw] range with a step=di.
31 *
32 * First, we start with cw = mw and select dests with weight >= cw.
33 * Then cw is reduced with di and all dests are checked again.
34 * Last pass should be with cw = di. We have mw/di passes in total:
35 *
36 * pass 1: cw = max weight
37 * pass 2: cw = max weight - di
38 * pass 3: cw = max weight - 2 * di
39 * ...
40 * last pass: cw = di
41 *
42 * Weights are supposed to be >= di but we run in parallel with
43 * weight changes, it is possible some dest weight to be reduced
44 * below di, bad if it is the only available dest.
45 *
46 * So, we modify how mw is calculated, now it is reduced with (di - 1),
47 * so that last cw is 1 to catch such dests with weight below di:
48 * pass 1: cw = max weight - (di - 1)
49 * pass 2: cw = max weight - di - (di - 1)
50 * pass 3: cw = max weight - 2 * di - (di - 1)
51 * ...
52 * last pass: cw = 1
53 *
54 */
55
56 /*
57 * current destination pointer for weighted round-robin scheduling
58 */
59 struct ip_vs_wrr_mark {
60 struct ip_vs_dest *cl; /* current dest or head */
61 int cw; /* current weight */
62 int mw; /* maximum weight */
63 int di; /* decreasing interval */
64 struct rcu_head rcu_head;
65 };
66
67
ip_vs_wrr_gcd_weight(struct ip_vs_service * svc)68 static int ip_vs_wrr_gcd_weight(struct ip_vs_service *svc)
69 {
70 struct ip_vs_dest *dest;
71 int weight;
72 int g = 0;
73
74 list_for_each_entry(dest, &svc->destinations, n_list) {
75 weight = atomic_read(&dest->weight);
76 if (weight > 0) {
77 if (g > 0)
78 g = gcd(weight, g);
79 else
80 g = weight;
81 }
82 }
83 return g ? g : 1;
84 }
85
86
87 /*
88 * Get the maximum weight of the service destinations.
89 */
ip_vs_wrr_max_weight(struct ip_vs_service * svc)90 static int ip_vs_wrr_max_weight(struct ip_vs_service *svc)
91 {
92 struct ip_vs_dest *dest;
93 int new_weight, weight = 0;
94
95 list_for_each_entry(dest, &svc->destinations, n_list) {
96 new_weight = atomic_read(&dest->weight);
97 if (new_weight > weight)
98 weight = new_weight;
99 }
100
101 return weight;
102 }
103
104
ip_vs_wrr_init_svc(struct ip_vs_service * svc)105 static int ip_vs_wrr_init_svc(struct ip_vs_service *svc)
106 {
107 struct ip_vs_wrr_mark *mark;
108
109 /*
110 * Allocate the mark variable for WRR scheduling
111 */
112 mark = kmalloc_obj(struct ip_vs_wrr_mark);
113 if (mark == NULL)
114 return -ENOMEM;
115
116 mark->cl = list_entry(&svc->destinations, struct ip_vs_dest, n_list);
117 mark->di = ip_vs_wrr_gcd_weight(svc);
118 mark->mw = ip_vs_wrr_max_weight(svc) - (mark->di - 1);
119 mark->cw = mark->mw;
120 svc->sched_data = mark;
121
122 return 0;
123 }
124
125
ip_vs_wrr_done_svc(struct ip_vs_service * svc)126 static void ip_vs_wrr_done_svc(struct ip_vs_service *svc)
127 {
128 struct ip_vs_wrr_mark *mark = svc->sched_data;
129
130 /*
131 * Release the mark variable
132 */
133 kfree_rcu(mark, rcu_head);
134 }
135
136
ip_vs_wrr_dest_changed(struct ip_vs_service * svc,struct ip_vs_dest * dest)137 static int ip_vs_wrr_dest_changed(struct ip_vs_service *svc,
138 struct ip_vs_dest *dest)
139 {
140 struct ip_vs_wrr_mark *mark = svc->sched_data;
141
142 spin_lock_bh(&svc->sched_lock);
143 mark->cl = list_entry(&svc->destinations, struct ip_vs_dest, n_list);
144 mark->di = ip_vs_wrr_gcd_weight(svc);
145 mark->mw = ip_vs_wrr_max_weight(svc) - (mark->di - 1);
146 if (mark->cw > mark->mw || !mark->cw)
147 mark->cw = mark->mw;
148 else if (mark->di > 1)
149 mark->cw = (mark->cw / mark->di) * mark->di + 1;
150 spin_unlock_bh(&svc->sched_lock);
151 return 0;
152 }
153
154
155 /*
156 * Weighted Round-Robin Scheduling
157 */
158 static struct ip_vs_dest *
ip_vs_wrr_schedule(struct ip_vs_service * svc,const struct sk_buff * skb,struct ip_vs_iphdr * iph)159 ip_vs_wrr_schedule(struct ip_vs_service *svc, const struct sk_buff *skb,
160 struct ip_vs_iphdr *iph)
161 {
162 struct ip_vs_dest *dest, *last, *stop = NULL;
163 struct ip_vs_wrr_mark *mark = svc->sched_data;
164 bool last_pass = false, restarted = false;
165
166 IP_VS_DBG(6, "%s(): Scheduling...\n", __func__);
167
168 spin_lock_bh(&svc->sched_lock);
169 dest = mark->cl;
170 /* No available dests? */
171 if (mark->mw == 0)
172 goto err_noavail;
173 last = dest;
174 /* Stop only after all dests were checked for weight >= 1 (last pass) */
175 while (1) {
176 list_for_each_entry_continue_rcu(dest,
177 &svc->destinations,
178 n_list) {
179 if (!(dest->flags & IP_VS_DEST_F_OVERLOAD) &&
180 atomic_read(&dest->weight) >= mark->cw)
181 goto found;
182 if (dest == stop)
183 goto err_over;
184 }
185 mark->cw -= mark->di;
186 if (mark->cw <= 0) {
187 mark->cw = mark->mw;
188 /* Stop if we tried last pass from first dest:
189 * 1. last_pass: we started checks when cw > di but
190 * then all dests were checked for w >= 1
191 * 2. last was head: the first and only traversal
192 * was for weight >= 1, for all dests.
193 */
194 if (last_pass ||
195 &last->n_list == &svc->destinations)
196 goto err_over;
197 restarted = true;
198 }
199 last_pass = mark->cw <= mark->di;
200 if (last_pass && restarted &&
201 &last->n_list != &svc->destinations) {
202 /* First traversal was for w >= 1 but only
203 * for dests after 'last', now do the same
204 * for all dests up to 'last'.
205 */
206 stop = last;
207 }
208 }
209
210 found:
211 IP_VS_DBG_BUF(6, "WRR: server %s:%u "
212 "activeconns %d refcnt %d weight %d\n",
213 IP_VS_DBG_ADDR(dest->af, &dest->addr), ntohs(dest->port),
214 atomic_read(&dest->activeconns),
215 refcount_read(&dest->refcnt),
216 atomic_read(&dest->weight));
217 mark->cl = dest;
218
219 out:
220 spin_unlock_bh(&svc->sched_lock);
221 return dest;
222
223 err_noavail:
224 mark->cl = dest;
225 dest = NULL;
226 ip_vs_scheduler_err(svc, "no destination available");
227 goto out;
228
229 err_over:
230 mark->cl = dest;
231 dest = NULL;
232 ip_vs_scheduler_err(svc, "no destination available: "
233 "all destinations are overloaded");
234 goto out;
235 }
236
237
238 static struct ip_vs_scheduler ip_vs_wrr_scheduler = {
239 .name = "wrr",
240 .refcnt = ATOMIC_INIT(0),
241 .module = THIS_MODULE,
242 .n_list = LIST_HEAD_INIT(ip_vs_wrr_scheduler.n_list),
243 .init_service = ip_vs_wrr_init_svc,
244 .done_service = ip_vs_wrr_done_svc,
245 .add_dest = ip_vs_wrr_dest_changed,
246 .del_dest = ip_vs_wrr_dest_changed,
247 .upd_dest = ip_vs_wrr_dest_changed,
248 .schedule = ip_vs_wrr_schedule,
249 };
250
ip_vs_wrr_init(void)251 static int __init ip_vs_wrr_init(void)
252 {
253 return register_ip_vs_scheduler(&ip_vs_wrr_scheduler) ;
254 }
255
ip_vs_wrr_cleanup(void)256 static void __exit ip_vs_wrr_cleanup(void)
257 {
258 unregister_ip_vs_scheduler(&ip_vs_wrr_scheduler);
259 synchronize_rcu();
260 }
261
262 module_init(ip_vs_wrr_init);
263 module_exit(ip_vs_wrr_cleanup);
264 MODULE_LICENSE("GPL");
265 MODULE_DESCRIPTION("ipvs weighted round-robin scheduler");
266