1 /* 2 * IPVS: Shortest Expected Delay 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 SED algorithm attempts to minimize each job's expected delay until 17 * completion. The expected delay that the job will experience is 18 * (Ci + 1) / Ui if sent to the ith server, in which Ci is the number of 19 * jobs on the ith server and Ui is the fixed service rate (weight) of 20 * the ith server. The SED algorithm adopts a greedy policy that each does 21 * what is in its own best interest, i.e. to join the queue which would 22 * minimize its expected delay of completion. 23 * 24 * See the following paper for more information: 25 * A. Weinrib and S. Shenker, Greed is not enough: Adaptive load sharing 26 * in large heterogeneous systems. In Proceedings IEEE INFOCOM'88, 27 * pages 986-994, 1988. 28 * 29 * Thanks must go to Marko Buuri <marko@buuri.name> for talking SED to me. 30 * 31 * The difference between SED and WLC is that SED includes the incoming 32 * job in the cost function (the increment of 1). SED may outperform 33 * WLC, while scheduling big jobs under larger heterogeneous systems 34 * (the server weight varies a lot). 35 * 36 */ 37 38 #define KMSG_COMPONENT "IPVS" 39 #define pr_fmt(fmt) KMSG_COMPONENT ": " fmt 40 41 #include <linux/module.h> 42 #include <linux/kernel.h> 43 44 #include <net/ip_vs.h> 45 46 47 static inline int 48 ip_vs_sed_dest_overhead(struct ip_vs_dest *dest) 49 { 50 /* 51 * We only use the active connection number in the cost 52 * calculation here. 53 */ 54 return atomic_read(&dest->activeconns) + 1; 55 } 56 57 58 /* 59 * Weighted Least Connection scheduling 60 */ 61 static struct ip_vs_dest * 62 ip_vs_sed_schedule(struct ip_vs_service *svc, const struct sk_buff *skb, 63 struct ip_vs_iphdr *iph) 64 { 65 struct ip_vs_dest *dest, *least; 66 int loh, doh; 67 68 IP_VS_DBG(6, "%s(): Scheduling...\n", __func__); 69 70 /* 71 * We calculate the load of each dest server as follows: 72 * (server expected overhead) / dest->weight 73 * 74 * Remember -- no floats in kernel mode!!! 75 * The comparison of h1*w2 > h2*w1 is equivalent to that of 76 * h1/w1 > h2/w2 77 * if every weight is larger than zero. 78 * 79 * The server with weight=0 is quiesced and will not receive any 80 * new connections. 81 */ 82 83 list_for_each_entry_rcu(dest, &svc->destinations, n_list) { 84 if (!(dest->flags & IP_VS_DEST_F_OVERLOAD) && 85 atomic_read(&dest->weight) > 0) { 86 least = dest; 87 loh = ip_vs_sed_dest_overhead(least); 88 goto nextstage; 89 } 90 } 91 ip_vs_scheduler_err(svc, "no destination available"); 92 return NULL; 93 94 /* 95 * Find the destination with the least load. 96 */ 97 nextstage: 98 list_for_each_entry_continue_rcu(dest, &svc->destinations, n_list) { 99 if (dest->flags & IP_VS_DEST_F_OVERLOAD) 100 continue; 101 doh = ip_vs_sed_dest_overhead(dest); 102 if ((__s64)loh * atomic_read(&dest->weight) > 103 (__s64)doh * atomic_read(&least->weight)) { 104 least = dest; 105 loh = doh; 106 } 107 } 108 109 IP_VS_DBG_BUF(6, "SED: server %s:%u " 110 "activeconns %d refcnt %d weight %d overhead %d\n", 111 IP_VS_DBG_ADDR(least->af, &least->addr), 112 ntohs(least->port), 113 atomic_read(&least->activeconns), 114 atomic_read(&least->refcnt), 115 atomic_read(&least->weight), loh); 116 117 return least; 118 } 119 120 121 static struct ip_vs_scheduler ip_vs_sed_scheduler = 122 { 123 .name = "sed", 124 .refcnt = ATOMIC_INIT(0), 125 .module = THIS_MODULE, 126 .n_list = LIST_HEAD_INIT(ip_vs_sed_scheduler.n_list), 127 .schedule = ip_vs_sed_schedule, 128 }; 129 130 131 static int __init ip_vs_sed_init(void) 132 { 133 return register_ip_vs_scheduler(&ip_vs_sed_scheduler); 134 } 135 136 static void __exit ip_vs_sed_cleanup(void) 137 { 138 unregister_ip_vs_scheduler(&ip_vs_sed_scheduler); 139 synchronize_rcu(); 140 } 141 142 module_init(ip_vs_sed_init); 143 module_exit(ip_vs_sed_cleanup); 144 MODULE_LICENSE("GPL"); 145