1 /*
2 * IPVS: Shortest Expected Delay 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 *
13 */
14
15 /*
16 * The SED algorithm attempts to minimize each job's expected delay until
17 * completion. The expected delay that the job will experience is
18 * (Ci + 1) / Ui if sent to the ith server, in which Ci is the number of
19 * jobs on the ith server and Ui is the fixed service rate (weight) of
20 * the ith server. The SED algorithm adopts a greedy policy that each does
21 * what is in its own best interest, i.e. to join the queue which would
22 * minimize its expected delay of completion.
23 *
24 * See the following paper for more information:
25 * A. Weinrib and S. Shenker, Greed is not enough: Adaptive load sharing
26 * in large heterogeneous systems. In Proceedings IEEE INFOCOM'88,
27 * pages 986-994, 1988.
28 *
29 * Thanks must go to Marko Buuri <marko@buuri.name> for talking SED to me.
30 *
31 * The difference between SED and WLC is that SED includes the incoming
32 * job in the cost function (the increment of 1). SED may outperform
33 * WLC, while scheduling big jobs under larger heterogeneous systems
34 * (the server weight varies a lot).
35 *
36 */
37
38 #define KMSG_COMPONENT "IPVS"
39 #define pr_fmt(fmt) KMSG_COMPONENT ": " fmt
40
41 #include <linux/module.h>
42 #include <linux/kernel.h>
43
44 #include <net/ip_vs.h>
45
46
47 static inline unsigned int
ip_vs_sed_dest_overhead(struct ip_vs_dest * dest)48 ip_vs_sed_dest_overhead(struct ip_vs_dest *dest)
49 {
50 /*
51 * We only use the active connection number in the cost
52 * calculation here.
53 */
54 return atomic_read(&dest->activeconns) + 1;
55 }
56
57
58 /*
59 * Weighted Least Connection scheduling
60 */
61 static struct ip_vs_dest *
ip_vs_sed_schedule(struct ip_vs_service * svc,const struct sk_buff * skb)62 ip_vs_sed_schedule(struct ip_vs_service *svc, const struct sk_buff *skb)
63 {
64 struct ip_vs_dest *dest, *least;
65 unsigned int loh, doh;
66
67 IP_VS_DBG(6, "%s(): Scheduling...\n", __func__);
68
69 /*
70 * We calculate the load of each dest server as follows:
71 * (server expected overhead) / dest->weight
72 *
73 * Remember -- no floats in kernel mode!!!
74 * The comparison of h1*w2 > h2*w1 is equivalent to that of
75 * h1/w1 > h2/w2
76 * if every weight is larger than zero.
77 *
78 * The server with weight=0 is quiesced and will not receive any
79 * new connections.
80 */
81
82 list_for_each_entry(dest, &svc->destinations, n_list) {
83 if (!(dest->flags & IP_VS_DEST_F_OVERLOAD) &&
84 atomic_read(&dest->weight) > 0) {
85 least = dest;
86 loh = ip_vs_sed_dest_overhead(least);
87 goto nextstage;
88 }
89 }
90 ip_vs_scheduler_err(svc, "no destination available");
91 return NULL;
92
93 /*
94 * Find the destination with the least load.
95 */
96 nextstage:
97 list_for_each_entry_continue(dest, &svc->destinations, n_list) {
98 if (dest->flags & IP_VS_DEST_F_OVERLOAD)
99 continue;
100 doh = ip_vs_sed_dest_overhead(dest);
101 if (loh * atomic_read(&dest->weight) >
102 doh * atomic_read(&least->weight)) {
103 least = dest;
104 loh = doh;
105 }
106 }
107
108 IP_VS_DBG_BUF(6, "SED: server %s:%u "
109 "activeconns %d refcnt %d weight %d overhead %d\n",
110 IP_VS_DBG_ADDR(svc->af, &least->addr), ntohs(least->port),
111 atomic_read(&least->activeconns),
112 atomic_read(&least->refcnt),
113 atomic_read(&least->weight), loh);
114
115 return least;
116 }
117
118
119 static struct ip_vs_scheduler ip_vs_sed_scheduler =
120 {
121 .name = "sed",
122 .refcnt = ATOMIC_INIT(0),
123 .module = THIS_MODULE,
124 .n_list = LIST_HEAD_INIT(ip_vs_sed_scheduler.n_list),
125 .schedule = ip_vs_sed_schedule,
126 };
127
128
ip_vs_sed_init(void)129 static int __init ip_vs_sed_init(void)
130 {
131 return register_ip_vs_scheduler(&ip_vs_sed_scheduler);
132 }
133
ip_vs_sed_cleanup(void)134 static void __exit ip_vs_sed_cleanup(void)
135 {
136 unregister_ip_vs_scheduler(&ip_vs_sed_scheduler);
137 }
138
139 module_init(ip_vs_sed_init);
140 module_exit(ip_vs_sed_cleanup);
141 MODULE_LICENSE("GPL");
142