1 /* 2 * IPVS: Never Queue scheduling module 3 * 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 #define KMSG_COMPONENT "IPVS" 35 #define pr_fmt(fmt) KMSG_COMPONENT ": " fmt 36 37 #include <linux/module.h> 38 #include <linux/kernel.h> 39 40 #include <net/ip_vs.h> 41 42 43 static inline int 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 * 58 ip_vs_nq_schedule(struct ip_vs_service *svc, const struct sk_buff *skb, 59 struct ip_vs_iphdr *iph) 60 { 61 struct ip_vs_dest *dest, *least = NULL; 62 int loh = 0, doh; 63 64 IP_VS_DBG(6, "%s(): Scheduling...\n", __func__); 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 79 list_for_each_entry_rcu(dest, &svc->destinations, n_list) { 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 || 95 ((__s64)loh * atomic_read(&dest->weight) > 96 (__s64)doh * atomic_read(&least->weight))) { 97 least = dest; 98 loh = doh; 99 } 100 } 101 102 if (!least) { 103 ip_vs_scheduler_err(svc, "no destination available"); 104 return NULL; 105 } 106 107 out: 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), 111 ntohs(least->port), 112 atomic_read(&least->activeconns), 113 refcount_read(&least->refcnt), 114 atomic_read(&least->weight), loh); 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, 125 .n_list = LIST_HEAD_INIT(ip_vs_nq_scheduler.n_list), 126 .schedule = ip_vs_nq_schedule, 127 }; 128 129 130 static int __init ip_vs_nq_init(void) 131 { 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); 138 synchronize_rcu(); 139 } 140 141 module_init(ip_vs_nq_init); 142 module_exit(ip_vs_nq_cleanup); 143 MODULE_LICENSE("GPL"); 144