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

source code of linux/net/netfilter/ipvs/ip_vs_wrr.c