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1da177e4 LT |
1 | /* |
2 | * IPVS: Never Queue scheduling module | |
3 | * | |
1da177e4 LT |
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 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). | |
21 | * | |
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. | |
26 | * | |
27 | * Thanks must go to Marko Buuri <marko@buuri.name> for talking NQ to me. | |
28 | * | |
29 | * The difference between NQ and SED is that NQ can improve overall | |
30 | * system utilization. | |
31 | * | |
32 | */ | |
33 | ||
9aada7ac HE |
34 | #define KMSG_COMPONENT "IPVS" |
35 | #define pr_fmt(fmt) KMSG_COMPONENT ": " fmt | |
36 | ||
1da177e4 LT |
37 | #include <linux/module.h> |
38 | #include <linux/kernel.h> | |
39 | ||
40 | #include <net/ip_vs.h> | |
41 | ||
42 | ||
c16526a7 | 43 | static inline int |
1da177e4 LT |
44 | ip_vs_nq_dest_overhead(struct ip_vs_dest *dest) |
45 | { | |
46 | /* | |
47 | * We only use the active connection number in the cost | |
48 | * calculation here. | |
49 | */ | |
50 | return atomic_read(&dest->activeconns) + 1; | |
51 | } | |
52 | ||
53 | ||
54 | /* | |
55 | * Weighted Least Connection scheduling | |
56 | */ | |
57 | static struct ip_vs_dest * | |
bba54de5 JA |
58 | ip_vs_nq_schedule(struct ip_vs_service *svc, const struct sk_buff *skb, |
59 | struct ip_vs_iphdr *iph) | |
1da177e4 LT |
60 | { |
61 | struct ip_vs_dest *dest, *least = NULL; | |
c16526a7 | 62 | int loh = 0, doh; |
1da177e4 | 63 | |
1e3e238e | 64 | IP_VS_DBG(6, "%s(): Scheduling...\n", __func__); |
1da177e4 LT |
65 | |
66 | /* | |
67 | * We calculate the load of each dest server as follows: | |
68 | * (server expected overhead) / dest->weight | |
69 | * | |
70 | * Remember -- no floats in kernel mode!!! | |
71 | * The comparison of h1*w2 > h2*w1 is equivalent to that of | |
72 | * h1/w1 > h2/w2 | |
73 | * if every weight is larger than zero. | |
74 | * | |
75 | * The server with weight=0 is quiesced and will not receive any | |
76 | * new connections. | |
77 | */ | |
78 | ||
f92ea8f0 | 79 | list_for_each_entry_rcu(dest, &svc->destinations, n_list) { |
1da177e4 LT |
80 | |
81 | if (dest->flags & IP_VS_DEST_F_OVERLOAD || | |
82 | !atomic_read(&dest->weight)) | |
83 | continue; | |
84 | ||
85 | doh = ip_vs_nq_dest_overhead(dest); | |
86 | ||
87 | /* return the server directly if it is idle */ | |
88 | if (atomic_read(&dest->activeconns) == 0) { | |
89 | least = dest; | |
90 | loh = doh; | |
91 | goto out; | |
92 | } | |
93 | ||
94 | if (!least || | |
c16526a7 SK |
95 | ((__s64)loh * atomic_read(&dest->weight) > |
96 | (__s64)doh * atomic_read(&least->weight))) { | |
1da177e4 LT |
97 | least = dest; |
98 | loh = doh; | |
99 | } | |
100 | } | |
101 | ||
68888d10 | 102 | if (!least) { |
41ac51ee | 103 | ip_vs_scheduler_err(svc, "no destination available"); |
1da177e4 | 104 | return NULL; |
68888d10 | 105 | } |
1da177e4 LT |
106 | |
107 | out: | |
b14198f6 JV |
108 | IP_VS_DBG_BUF(6, "NQ: server %s:%u " |
109 | "activeconns %d refcnt %d weight %d overhead %d\n", | |
4d316f3f JA |
110 | IP_VS_DBG_ADDR(least->af, &least->addr), |
111 | ntohs(least->port), | |
b14198f6 JV |
112 | atomic_read(&least->activeconns), |
113 | atomic_read(&least->refcnt), | |
114 | atomic_read(&least->weight), loh); | |
1da177e4 LT |
115 | |
116 | return least; | |
117 | } | |
118 | ||
119 | ||
120 | static struct ip_vs_scheduler ip_vs_nq_scheduler = | |
121 | { | |
122 | .name = "nq", | |
123 | .refcnt = ATOMIC_INIT(0), | |
124 | .module = THIS_MODULE, | |
d149ccc9 | 125 | .n_list = LIST_HEAD_INIT(ip_vs_nq_scheduler.n_list), |
1da177e4 LT |
126 | .schedule = ip_vs_nq_schedule, |
127 | }; | |
128 | ||
129 | ||
130 | static int __init ip_vs_nq_init(void) | |
131 | { | |
1da177e4 LT |
132 | return register_ip_vs_scheduler(&ip_vs_nq_scheduler); |
133 | } | |
134 | ||
135 | static void __exit ip_vs_nq_cleanup(void) | |
136 | { | |
137 | unregister_ip_vs_scheduler(&ip_vs_nq_scheduler); | |
ceec4c38 | 138 | synchronize_rcu(); |
1da177e4 LT |
139 | } |
140 | ||
141 | module_init(ip_vs_nq_init); | |
142 | module_exit(ip_vs_nq_cleanup); | |
143 | MODULE_LICENSE("GPL"); |