2 * IPVS: Shortest Expected Delay scheduling module
4 * Authors: Wensong Zhang <wensong@linuxvirtualserver.org>
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.
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.
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.
29 * Thanks must go to Marko Buuri <marko@buuri.name> for talking SED to me.
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).
38 #include <linux/module.h>
39 #include <linux/kernel.h>
41 #include <net/ip_vs.h>
44 static inline unsigned int
45 ip_vs_sed_dest_overhead(struct ip_vs_dest *dest)
48 * We only use the active connection number in the cost
51 return atomic_read(&dest->activeconns) + 1;
56 * Weighted Least Connection scheduling
58 static struct ip_vs_dest *
59 ip_vs_sed_schedule(struct ip_vs_service *svc, const struct sk_buff *skb)
61 struct ip_vs_dest *dest, *least;
62 unsigned int loh, doh;
64 IP_VS_DBG(6, "ip_vs_sed_schedule(): Scheduling...\n");
67 * We calculate the load of each dest server as follows:
68 * (server expected overhead) / dest->weight
70 * Remember -- no floats in kernel mode!!!
71 * The comparison of h1*w2 > h2*w1 is equivalent to that of
73 * if every weight is larger than zero.
75 * The server with weight=0 is quiesced and will not receive any
79 list_for_each_entry(dest, &svc->destinations, n_list) {
80 if (!(dest->flags & IP_VS_DEST_F_OVERLOAD) &&
81 atomic_read(&dest->weight) > 0) {
83 loh = ip_vs_sed_dest_overhead(least);
90 * Find the destination with the least load.
93 list_for_each_entry_continue(dest, &svc->destinations, n_list) {
94 if (dest->flags & IP_VS_DEST_F_OVERLOAD)
96 doh = ip_vs_sed_dest_overhead(dest);
97 if (loh * atomic_read(&dest->weight) >
98 doh * atomic_read(&least->weight)) {
104 IP_VS_DBG(6, "SED: server %u.%u.%u.%u:%u "
105 "activeconns %d refcnt %d weight %d overhead %d\n",
106 NIPQUAD(least->addr.ip), ntohs(least->port),
107 atomic_read(&least->activeconns),
108 atomic_read(&least->refcnt),
109 atomic_read(&least->weight), loh);
115 static struct ip_vs_scheduler ip_vs_sed_scheduler =
118 .refcnt = ATOMIC_INIT(0),
119 .module = THIS_MODULE,
120 .n_list = LIST_HEAD_INIT(ip_vs_sed_scheduler.n_list),
121 .schedule = ip_vs_sed_schedule,
125 static int __init ip_vs_sed_init(void)
127 return register_ip_vs_scheduler(&ip_vs_sed_scheduler);
130 static void __exit ip_vs_sed_cleanup(void)
132 unregister_ip_vs_scheduler(&ip_vs_sed_scheduler);
135 module_init(ip_vs_sed_init);
136 module_exit(ip_vs_sed_cleanup);
137 MODULE_LICENSE("GPL");