1 | // SPDX-License-Identifier: GPL-2.0-or-later |
2 | /* |
3 | * IPVS: Never Queue scheduling module |
4 | * |
5 | * Authors: Wensong Zhang <wensong@linuxvirtualserver.org> |
6 | * |
7 | * Changes: |
8 | */ |
9 | |
10 | /* |
11 | * The NQ algorithm adopts a two-speed model. When there is an idle server |
12 | * available, the job will be sent to the idle server, instead of waiting |
13 | * for a fast one. When there is no idle server available, the job will be |
14 | * sent to the server that minimize its expected delay (The Shortest |
15 | * Expected Delay scheduling algorithm). |
16 | * |
17 | * See the following paper for more information: |
18 | * A. Weinrib and S. Shenker, Greed is not enough: Adaptive load sharing |
19 | * in large heterogeneous systems. In Proceedings IEEE INFOCOM'88, |
20 | * pages 986-994, 1988. |
21 | * |
22 | * Thanks must go to Marko Buuri <marko@buuri.name> for talking NQ to me. |
23 | * |
24 | * The difference between NQ and SED is that NQ can improve overall |
25 | * system utilization. |
26 | * |
27 | */ |
28 | |
29 | #define KMSG_COMPONENT "IPVS" |
30 | #define pr_fmt(fmt) KMSG_COMPONENT ": " fmt |
31 | |
32 | #include <linux/module.h> |
33 | #include <linux/kernel.h> |
34 | |
35 | #include <net/ip_vs.h> |
36 | |
37 | |
38 | static inline int |
39 | ip_vs_nq_dest_overhead(struct ip_vs_dest *dest) |
40 | { |
41 | /* |
42 | * We only use the active connection number in the cost |
43 | * calculation here. |
44 | */ |
45 | return atomic_read(v: &dest->activeconns) + 1; |
46 | } |
47 | |
48 | |
49 | /* |
50 | * Weighted Least Connection scheduling |
51 | */ |
52 | static struct ip_vs_dest * |
53 | ip_vs_nq_schedule(struct ip_vs_service *svc, const struct sk_buff *skb, |
54 | struct ip_vs_iphdr *iph) |
55 | { |
56 | struct ip_vs_dest *dest, *least = NULL; |
57 | int loh = 0, doh; |
58 | |
59 | IP_VS_DBG(6, "%s(): Scheduling...\n" , __func__); |
60 | |
61 | /* |
62 | * We calculate the load of each dest server as follows: |
63 | * (server expected overhead) / dest->weight |
64 | * |
65 | * Remember -- no floats in kernel mode!!! |
66 | * The comparison of h1*w2 > h2*w1 is equivalent to that of |
67 | * h1/w1 > h2/w2 |
68 | * if every weight is larger than zero. |
69 | * |
70 | * The server with weight=0 is quiesced and will not receive any |
71 | * new connections. |
72 | */ |
73 | |
74 | list_for_each_entry_rcu(dest, &svc->destinations, n_list) { |
75 | |
76 | if (dest->flags & IP_VS_DEST_F_OVERLOAD || |
77 | !atomic_read(v: &dest->weight)) |
78 | continue; |
79 | |
80 | doh = ip_vs_nq_dest_overhead(dest); |
81 | |
82 | /* return the server directly if it is idle */ |
83 | if (atomic_read(v: &dest->activeconns) == 0) { |
84 | least = dest; |
85 | loh = doh; |
86 | goto out; |
87 | } |
88 | |
89 | if (!least || |
90 | ((__s64)loh * atomic_read(v: &dest->weight) > |
91 | (__s64)doh * atomic_read(v: &least->weight))) { |
92 | least = dest; |
93 | loh = doh; |
94 | } |
95 | } |
96 | |
97 | if (!least) { |
98 | ip_vs_scheduler_err(svc, msg: "no destination available" ); |
99 | return NULL; |
100 | } |
101 | |
102 | out: |
103 | IP_VS_DBG_BUF(6, "NQ: server %s:%u " |
104 | "activeconns %d refcnt %d weight %d overhead %d\n" , |
105 | IP_VS_DBG_ADDR(least->af, &least->addr), |
106 | ntohs(least->port), |
107 | atomic_read(&least->activeconns), |
108 | refcount_read(&least->refcnt), |
109 | atomic_read(&least->weight), loh); |
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, |
120 | .n_list = LIST_HEAD_INIT(ip_vs_nq_scheduler.n_list), |
121 | .schedule = ip_vs_nq_schedule, |
122 | }; |
123 | |
124 | |
125 | static int __init ip_vs_nq_init(void) |
126 | { |
127 | return register_ip_vs_scheduler(scheduler: &ip_vs_nq_scheduler); |
128 | } |
129 | |
130 | static void __exit ip_vs_nq_cleanup(void) |
131 | { |
132 | unregister_ip_vs_scheduler(scheduler: &ip_vs_nq_scheduler); |
133 | synchronize_rcu(); |
134 | } |
135 | |
136 | module_init(ip_vs_nq_init); |
137 | module_exit(ip_vs_nq_cleanup); |
138 | MODULE_LICENSE("GPL" ); |
139 | MODULE_DESCRIPTION("ipvs never queue scheduler" ); |
140 | |