2 * IPVS: Never Queue 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 NQ algorithm adopts a two-speed model. When there is an idle server
17 * available, the job will be sent to the idle server, instead of waiting
18 * for a fast one. When there is no idle server available, the job will be
19 * sent to the server that minimize its expected delay (The Shortest
20 * Expected Delay scheduling algorithm).
22 * See the following paper for more information:
23 * A. Weinrib and S. Shenker, Greed is not enough: Adaptive load sharing
24 * in large heterogeneous systems. In Proceedings IEEE INFOCOM'88,
25 * pages 986-994, 1988.
27 * Thanks must go to Marko Buuri <marko@buuri.name> for talking NQ to me.
29 * The difference between NQ and SED is that NQ can improve overall
34 #define KMSG_COMPONENT "IPVS"
35 #define pr_fmt(fmt) KMSG_COMPONENT ": " fmt
37 #include <linux/module.h>
38 #include <linux/kernel.h>
40 #include <net/ip_vs.h>
44 ip_vs_nq_dest_overhead(struct ip_vs_dest
*dest
)
47 * We only use the active connection number in the cost
50 return atomic_read(&dest
->activeconns
) + 1;
55 * Weighted Least Connection scheduling
57 static struct ip_vs_dest
*
58 ip_vs_nq_schedule(struct ip_vs_service
*svc
, const struct sk_buff
*skb
,
59 struct ip_vs_iphdr
*iph
)
61 struct ip_vs_dest
*dest
, *least
= NULL
;
64 IP_VS_DBG(6, "%s(): Scheduling...\n", __func__
);
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_rcu(dest
, &svc
->destinations
, n_list
) {
81 if (dest
->flags
& IP_VS_DEST_F_OVERLOAD
||
82 !atomic_read(&dest
->weight
))
85 doh
= ip_vs_nq_dest_overhead(dest
);
87 /* return the server directly if it is idle */
88 if (atomic_read(&dest
->activeconns
) == 0) {
95 ((__s64
)loh
* atomic_read(&dest
->weight
) >
96 (__s64
)doh
* atomic_read(&least
->weight
))) {
103 ip_vs_scheduler_err(svc
, "no destination available");
108 IP_VS_DBG_BUF(6, "NQ: server %s:%u "
109 "activeconns %d refcnt %d weight %d overhead %d\n",
110 IP_VS_DBG_ADDR(least
->af
, &least
->addr
),
112 atomic_read(&least
->activeconns
),
113 atomic_read(&least
->refcnt
),
114 atomic_read(&least
->weight
), loh
);
120 static struct ip_vs_scheduler ip_vs_nq_scheduler
=
123 .refcnt
= ATOMIC_INIT(0),
124 .module
= THIS_MODULE
,
125 .n_list
= LIST_HEAD_INIT(ip_vs_nq_scheduler
.n_list
),
126 .schedule
= ip_vs_nq_schedule
,
130 static int __init
ip_vs_nq_init(void)
132 return register_ip_vs_scheduler(&ip_vs_nq_scheduler
);
135 static void __exit
ip_vs_nq_cleanup(void)
137 unregister_ip_vs_scheduler(&ip_vs_nq_scheduler
);
141 module_init(ip_vs_nq_init
);
142 module_exit(ip_vs_nq_cleanup
);
143 MODULE_LICENSE("GPL");