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1 | // SPDX-License-Identifier: GPL-2.0-or-later | |
2 | /* | |
3 | * IPVS: Shortest Expected Delay scheduling module | |
4 | * | |
5 | * Authors: Wensong Zhang <wensong@linuxvirtualserver.org> | |
6 | * | |
7 | * Changes: | |
8 | */ | |
9 | ||
10 | /* | |
11 | * The SED algorithm attempts to minimize each job's expected delay until | |
12 | * completion. The expected delay that the job will experience is | |
13 | * (Ci + 1) / Ui if sent to the ith server, in which Ci is the number of | |
14 | * jobs on the ith server and Ui is the fixed service rate (weight) of | |
15 | * the ith server. The SED algorithm adopts a greedy policy that each does | |
16 | * what is in its own best interest, i.e. to join the queue which would | |
17 | * minimize its expected delay of completion. | |
18 | * | |
19 | * See the following paper for more information: | |
20 | * A. Weinrib and S. Shenker, Greed is not enough: Adaptive load sharing | |
21 | * in large heterogeneous systems. In Proceedings IEEE INFOCOM'88, | |
22 | * pages 986-994, 1988. | |
23 | * | |
24 | * Thanks must go to Marko Buuri <marko@buuri.name> for talking SED to me. | |
25 | * | |
26 | * The difference between SED and WLC is that SED includes the incoming | |
27 | * job in the cost function (the increment of 1). SED may outperform | |
28 | * WLC, while scheduling big jobs under larger heterogeneous systems | |
29 | * (the server weight varies a lot). | |
30 | * | |
31 | */ | |
32 | ||
33 | #define KMSG_COMPONENT "IPVS" | |
34 | #define pr_fmt(fmt) KMSG_COMPONENT ": " fmt | |
35 | ||
36 | #include <linux/module.h> | |
37 | #include <linux/kernel.h> | |
38 | ||
39 | #include <net/ip_vs.h> | |
40 | ||
41 | ||
42 | static inline int | |
43 | ip_vs_sed_dest_overhead(struct ip_vs_dest *dest) | |
44 | { | |
45 | /* | |
46 | * We only use the active connection number in the cost | |
47 | * calculation here. | |
48 | */ | |
49 | return atomic_read(&dest->activeconns) + 1; | |
50 | } | |
51 | ||
52 | ||
53 | /* | |
54 | * Weighted Least Connection scheduling | |
55 | */ | |
56 | static struct ip_vs_dest * | |
57 | ip_vs_sed_schedule(struct ip_vs_service *svc, const struct sk_buff *skb, | |
58 | struct ip_vs_iphdr *iph) | |
59 | { | |
60 | struct ip_vs_dest *dest, *least; | |
61 | int loh, doh; | |
62 | ||
63 | IP_VS_DBG(6, "%s(): Scheduling...\n", __func__); | |
64 | ||
65 | /* | |
66 | * We calculate the load of each dest server as follows: | |
67 | * (server expected overhead) / dest->weight | |
68 | * | |
69 | * Remember -- no floats in kernel mode!!! | |
70 | * The comparison of h1*w2 > h2*w1 is equivalent to that of | |
71 | * h1/w1 > h2/w2 | |
72 | * if every weight is larger than zero. | |
73 | * | |
74 | * The server with weight=0 is quiesced and will not receive any | |
75 | * new connections. | |
76 | */ | |
77 | ||
78 | list_for_each_entry_rcu(dest, &svc->destinations, n_list) { | |
79 | if (!(dest->flags & IP_VS_DEST_F_OVERLOAD) && | |
80 | atomic_read(&dest->weight) > 0) { | |
81 | least = dest; | |
82 | loh = ip_vs_sed_dest_overhead(least); | |
83 | goto nextstage; | |
84 | } | |
85 | } | |
86 | ip_vs_scheduler_err(svc, "no destination available"); | |
87 | return NULL; | |
88 | ||
89 | /* | |
90 | * Find the destination with the least load. | |
91 | */ | |
92 | nextstage: | |
93 | list_for_each_entry_continue_rcu(dest, &svc->destinations, n_list) { | |
94 | if (dest->flags & IP_VS_DEST_F_OVERLOAD) | |
95 | continue; | |
96 | doh = ip_vs_sed_dest_overhead(dest); | |
97 | if ((__s64)loh * atomic_read(&dest->weight) > | |
98 | (__s64)doh * atomic_read(&least->weight)) { | |
99 | least = dest; | |
100 | loh = doh; | |
101 | } | |
102 | } | |
103 | ||
104 | IP_VS_DBG_BUF(6, "SED: server %s:%u " | |
105 | "activeconns %d refcnt %d weight %d overhead %d\n", | |
106 | IP_VS_DBG_ADDR(least->af, &least->addr), | |
107 | ntohs(least->port), | |
108 | atomic_read(&least->activeconns), | |
109 | refcount_read(&least->refcnt), | |
110 | atomic_read(&least->weight), loh); | |
111 | ||
112 | return least; | |
113 | } | |
114 | ||
115 | ||
116 | static struct ip_vs_scheduler ip_vs_sed_scheduler = | |
117 | { | |
118 | .name = "sed", | |
119 | .refcnt = ATOMIC_INIT(0), | |
120 | .module = THIS_MODULE, | |
121 | .n_list = LIST_HEAD_INIT(ip_vs_sed_scheduler.n_list), | |
122 | .schedule = ip_vs_sed_schedule, | |
123 | }; | |
124 | ||
125 | ||
126 | static int __init ip_vs_sed_init(void) | |
127 | { | |
128 | return register_ip_vs_scheduler(&ip_vs_sed_scheduler); | |
129 | } | |
130 | ||
131 | static void __exit ip_vs_sed_cleanup(void) | |
132 | { | |
133 | unregister_ip_vs_scheduler(&ip_vs_sed_scheduler); | |
134 | synchronize_rcu(); | |
135 | } | |
136 | ||
137 | module_init(ip_vs_sed_init); | |
138 | module_exit(ip_vs_sed_cleanup); | |
139 | MODULE_LICENSE("GPL"); |