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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 | ||
34 | #include <linux/module.h> | |
35 | #include <linux/kernel.h> | |
36 | ||
37 | #include <net/ip_vs.h> | |
38 | ||
39 | ||
1da177e4 LT |
40 | static inline unsigned int |
41 | ip_vs_nq_dest_overhead(struct ip_vs_dest *dest) | |
42 | { | |
43 | /* | |
44 | * We only use the active connection number in the cost | |
45 | * calculation here. | |
46 | */ | |
47 | return atomic_read(&dest->activeconns) + 1; | |
48 | } | |
49 | ||
50 | ||
51 | /* | |
52 | * Weighted Least Connection scheduling | |
53 | */ | |
54 | static struct ip_vs_dest * | |
55 | ip_vs_nq_schedule(struct ip_vs_service *svc, const struct sk_buff *skb) | |
56 | { | |
57 | struct ip_vs_dest *dest, *least = NULL; | |
58 | unsigned int loh = 0, doh; | |
59 | ||
60 | IP_VS_DBG(6, "ip_vs_nq_schedule(): Scheduling...\n"); | |
61 | ||
62 | /* | |
63 | * We calculate the load of each dest server as follows: | |
64 | * (server expected overhead) / dest->weight | |
65 | * | |
66 | * Remember -- no floats in kernel mode!!! | |
67 | * The comparison of h1*w2 > h2*w1 is equivalent to that of | |
68 | * h1/w1 > h2/w2 | |
69 | * if every weight is larger than zero. | |
70 | * | |
71 | * The server with weight=0 is quiesced and will not receive any | |
72 | * new connections. | |
73 | */ | |
74 | ||
75 | list_for_each_entry(dest, &svc->destinations, n_list) { | |
76 | ||
77 | if (dest->flags & IP_VS_DEST_F_OVERLOAD || | |
78 | !atomic_read(&dest->weight)) | |
79 | continue; | |
80 | ||
81 | doh = ip_vs_nq_dest_overhead(dest); | |
82 | ||
83 | /* return the server directly if it is idle */ | |
84 | if (atomic_read(&dest->activeconns) == 0) { | |
85 | least = dest; | |
86 | loh = doh; | |
87 | goto out; | |
88 | } | |
89 | ||
90 | if (!least || | |
91 | (loh * atomic_read(&dest->weight) > | |
92 | doh * atomic_read(&least->weight))) { | |
93 | least = dest; | |
94 | loh = doh; | |
95 | } | |
96 | } | |
97 | ||
68888d10 SH |
98 | if (!least) { |
99 | IP_VS_ERR_RL("NQ: no destination available\n"); | |
1da177e4 | 100 | return NULL; |
68888d10 | 101 | } |
1da177e4 LT |
102 | |
103 | out: | |
b14198f6 JV |
104 | IP_VS_DBG_BUF(6, "NQ: server %s:%u " |
105 | "activeconns %d refcnt %d weight %d overhead %d\n", | |
106 | IP_VS_DBG_ADDR(svc->af, &least->addr), ntohs(least->port), | |
107 | atomic_read(&least->activeconns), | |
108 | atomic_read(&least->refcnt), | |
109 | atomic_read(&least->weight), loh); | |
1da177e4 LT |
110 | |
111 | return least; | |
112 | } | |
113 | ||
114 | ||
115 | static struct ip_vs_scheduler ip_vs_nq_scheduler = | |
116 | { | |
117 | .name = "nq", | |
118 | .refcnt = ATOMIC_INIT(0), | |
119 | .module = THIS_MODULE, | |
d149ccc9 | 120 | .n_list = LIST_HEAD_INIT(ip_vs_nq_scheduler.n_list), |
1da177e4 LT |
121 | .schedule = ip_vs_nq_schedule, |
122 | }; | |
123 | ||
124 | ||
125 | static int __init ip_vs_nq_init(void) | |
126 | { | |
1da177e4 LT |
127 | return register_ip_vs_scheduler(&ip_vs_nq_scheduler); |
128 | } | |
129 | ||
130 | static void __exit ip_vs_nq_cleanup(void) | |
131 | { | |
132 | unregister_ip_vs_scheduler(&ip_vs_nq_scheduler); | |
133 | } | |
134 | ||
135 | module_init(ip_vs_nq_init); | |
136 | module_exit(ip_vs_nq_cleanup); | |
137 | MODULE_LICENSE("GPL"); |