1/*
2 * IPVS:        Never Queue scheduling module
3 *
4 * Version:     $Id: ip_vs_nq.c,v 1.1.1.1 2007/08/03 18:53:51 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 NQ algorithm adopts a two-speed model. When there is an idle server
19 * available, the job will be sent to the idle server, instead of waiting
20 * for a fast one. When there is no idle server available, the job will be
21 * sent to the server that minimize its expected delay (The Shortest
22 * Expected Delay scheduling algorithm).
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 NQ to me.
30 *
31 * The difference between NQ and SED is that NQ can improve overall
32 * system utilization.
33 *
34 */
35
36#include <linux/module.h>
37#include <linux/kernel.h>
38
39#include <net/ip_vs.h>
40
41
42static int
43ip_vs_nq_init_svc(struct ip_vs_service *svc)
44{
45	return 0;
46}
47
48
49static int
50ip_vs_nq_done_svc(struct ip_vs_service *svc)
51{
52	return 0;
53}
54
55
56static int
57ip_vs_nq_update_svc(struct ip_vs_service *svc)
58{
59	return 0;
60}
61
62
63static inline unsigned int
64ip_vs_nq_dest_overhead(struct ip_vs_dest *dest)
65{
66	/*
67	 * We only use the active connection number in the cost
68	 * calculation here.
69	 */
70	return atomic_read(&dest->activeconns) + 1;
71}
72
73
74/*
75 *	Weighted Least Connection scheduling
76 */
77static struct ip_vs_dest *
78ip_vs_nq_schedule(struct ip_vs_service *svc, const struct sk_buff *skb)
79{
80	struct ip_vs_dest *dest, *least = NULL;
81	unsigned int loh = 0, doh;
82
83	IP_VS_DBG(6, "ip_vs_nq_schedule(): Scheduling...\n");
84
85	/*
86	 * We calculate the load of each dest server as follows:
87	 *	(server expected overhead) / dest->weight
88	 *
89	 * Remember -- no floats in kernel mode!!!
90	 * The comparison of h1*w2 > h2*w1 is equivalent to that of
91	 *		  h1/w1 > h2/w2
92	 * if every weight is larger than zero.
93	 *
94	 * The server with weight=0 is quiesced and will not receive any
95	 * new connections.
96	 */
97
98	list_for_each_entry(dest, &svc->destinations, n_list) {
99
100		if (dest->flags & IP_VS_DEST_F_OVERLOAD ||
101		    !atomic_read(&dest->weight))
102			continue;
103
104		doh = ip_vs_nq_dest_overhead(dest);
105
106		/* return the server directly if it is idle */
107		if (atomic_read(&dest->activeconns) == 0) {
108			least = dest;
109			loh = doh;
110			goto out;
111		}
112
113		if (!least ||
114		    (loh * atomic_read(&dest->weight) >
115		     doh * atomic_read(&least->weight))) {
116			least = dest;
117			loh = doh;
118		}
119	}
120
121	if (!least)
122		return NULL;
123
124  out:
125	IP_VS_DBG(6, "NQ: server %u.%u.%u.%u:%u "
126		  "activeconns %d refcnt %d weight %d overhead %d\n",
127		  NIPQUAD(least->addr), ntohs(least->port),
128		  atomic_read(&least->activeconns),
129		  atomic_read(&least->refcnt),
130		  atomic_read(&least->weight), loh);
131
132	return least;
133}
134
135
136static struct ip_vs_scheduler ip_vs_nq_scheduler =
137{
138	.name =			"nq",
139	.refcnt =		ATOMIC_INIT(0),
140	.module =		THIS_MODULE,
141	.init_service =		ip_vs_nq_init_svc,
142	.done_service =		ip_vs_nq_done_svc,
143	.update_service =	ip_vs_nq_update_svc,
144	.schedule =		ip_vs_nq_schedule,
145};
146
147
148static int __init ip_vs_nq_init(void)
149{
150	INIT_LIST_HEAD(&ip_vs_nq_scheduler.n_list);
151	return register_ip_vs_scheduler(&ip_vs_nq_scheduler);
152}
153
154static void __exit ip_vs_nq_cleanup(void)
155{
156	unregister_ip_vs_scheduler(&ip_vs_nq_scheduler);
157}
158
159module_init(ip_vs_nq_init);
160module_exit(ip_vs_nq_cleanup);
161MODULE_LICENSE("GPL");
162