1/*
2 * IPVS:        Shortest Expected Delay scheduling module
3 *
4 * Version:     $Id: ip_vs_sed.c,v 1.1.1.1 2007/08/03 18:53:52 Exp $
5 *
6 * Authors:     Wensong Zhang <wensong@linuxvirtualserver.org>
7 *
8 *              This program is free software; you can redistribute it and/or
9 *              modify it under the terms of the GNU General Public License
10 *              as published by the Free Software Foundation; either version
11 *              2 of the License, or (at your option) any later version.
12 *
13 * Changes:
14 *
15 */
16
17/*
18 * The SED algorithm attempts to minimize each job's expected delay until
19 * completion. The expected delay that the job will experience is
20 * (Ci + 1) / Ui if sent to the ith server, in which Ci is the number of
21 * jobs on the ith server and Ui is the fixed service rate (weight) of
22 * the ith server. The SED algorithm adopts a greedy policy that each does
23 * what is in its own best interest, i.e. to join the queue which would
24 * minimize its expected delay of completion.
25 *
26 * See the following paper for more information:
27 * A. Weinrib and S. Shenker, Greed is not enough: Adaptive load sharing
28 * in large heterogeneous systems. In Proceedings IEEE INFOCOM'88,
29 * pages 986-994, 1988.
30 *
31 * Thanks must go to Marko Buuri <marko@buuri.name> for talking SED to me.
32 *
33 * The difference between SED and WLC is that SED includes the incoming
34 * job in the cost function (the increment of 1). SED may outperform
35 * WLC, while scheduling big jobs under larger heterogeneous systems
36 * (the server weight varies a lot).
37 *
38 */
39
40#include <linux/module.h>
41#include <linux/kernel.h>
42
43#include <net/ip_vs.h>
44
45
46static int
47ip_vs_sed_init_svc(struct ip_vs_service *svc)
48{
49	return 0;
50}
51
52
53static int
54ip_vs_sed_done_svc(struct ip_vs_service *svc)
55{
56	return 0;
57}
58
59
60static int
61ip_vs_sed_update_svc(struct ip_vs_service *svc)
62{
63	return 0;
64}
65
66
67static inline unsigned int
68ip_vs_sed_dest_overhead(struct ip_vs_dest *dest)
69{
70	/*
71	 * We only use the active connection number in the cost
72	 * calculation here.
73	 */
74	return atomic_read(&dest->activeconns) + 1;
75}
76
77
78/*
79 *	Weighted Least Connection scheduling
80 */
81static struct ip_vs_dest *
82ip_vs_sed_schedule(struct ip_vs_service *svc, const struct sk_buff *skb)
83{
84	struct ip_vs_dest *dest, *least;
85	unsigned int loh, doh;
86
87	IP_VS_DBG(6, "ip_vs_sed_schedule(): Scheduling...\n");
88
89	/*
90	 * We calculate the load of each dest server as follows:
91	 *	(server expected overhead) / dest->weight
92	 *
93	 * Remember -- no floats in kernel mode!!!
94	 * The comparison of h1*w2 > h2*w1 is equivalent to that of
95	 *		  h1/w1 > h2/w2
96	 * if every weight is larger than zero.
97	 *
98	 * The server with weight=0 is quiesced and will not receive any
99	 * new connections.
100	 */
101
102	list_for_each_entry(dest, &svc->destinations, n_list) {
103		if (!(dest->flags & IP_VS_DEST_F_OVERLOAD) &&
104		    atomic_read(&dest->weight) > 0) {
105			least = dest;
106			loh = ip_vs_sed_dest_overhead(least);
107			goto nextstage;
108		}
109	}
110	return NULL;
111
112	/*
113	 *    Find the destination with the least load.
114	 */
115  nextstage:
116	list_for_each_entry_continue(dest, &svc->destinations, n_list) {
117		if (dest->flags & IP_VS_DEST_F_OVERLOAD)
118			continue;
119		doh = ip_vs_sed_dest_overhead(dest);
120		if (loh * atomic_read(&dest->weight) >
121		    doh * atomic_read(&least->weight)) {
122			least = dest;
123			loh = doh;
124		}
125	}
126
127	IP_VS_DBG(6, "SED: server %u.%u.%u.%u:%u "
128		  "activeconns %d refcnt %d weight %d overhead %d\n",
129		  NIPQUAD(least->addr), ntohs(least->port),
130		  atomic_read(&least->activeconns),
131		  atomic_read(&least->refcnt),
132		  atomic_read(&least->weight), loh);
133
134	return least;
135}
136
137
138static struct ip_vs_scheduler ip_vs_sed_scheduler =
139{
140	.name =			"sed",
141	.refcnt =		ATOMIC_INIT(0),
142	.module =		THIS_MODULE,
143	.init_service =		ip_vs_sed_init_svc,
144	.done_service =		ip_vs_sed_done_svc,
145	.update_service =	ip_vs_sed_update_svc,
146	.schedule =		ip_vs_sed_schedule,
147};
148
149
150static int __init ip_vs_sed_init(void)
151{
152	INIT_LIST_HEAD(&ip_vs_sed_scheduler.n_list);
153	return register_ip_vs_scheduler(&ip_vs_sed_scheduler);
154}
155
156static void __exit ip_vs_sed_cleanup(void)
157{
158	unregister_ip_vs_scheduler(&ip_vs_sed_scheduler);
159}
160
161module_init(ip_vs_sed_init);
162module_exit(ip_vs_sed_cleanup);
163MODULE_LICENSE("GPL");
164