1/* 2 * IPVS: Shortest Expected Delay scheduling module 3 * 4 * Version: $Id: ip_vs_sed.c,v 1.1.1.1 2007/08/03 18:53:52 Exp $ 5 * 6 * Authors: Wensong Zhang <wensong@linuxvirtualserver.org> 7 * 8 * This program is free software; you can redistribute it and/or 9 * modify it under the terms of the GNU General Public License 10 * as published by the Free Software Foundation; either version 11 * 2 of the License, or (at your option) any later version. 12 * 13 * Changes: 14 * 15 */ 16 17/* 18 * The SED algorithm attempts to minimize each job's expected delay until 19 * completion. The expected delay that the job will experience is 20 * (Ci + 1) / Ui if sent to the ith server, in which Ci is the number of 21 * jobs on the ith server and Ui is the fixed service rate (weight) of 22 * the ith server. The SED algorithm adopts a greedy policy that each does 23 * what is in its own best interest, i.e. to join the queue which would 24 * minimize its expected delay of completion. 25 * 26 * See the following paper for more information: 27 * A. Weinrib and S. Shenker, Greed is not enough: Adaptive load sharing 28 * in large heterogeneous systems. In Proceedings IEEE INFOCOM'88, 29 * pages 986-994, 1988. 30 * 31 * Thanks must go to Marko Buuri <marko@buuri.name> for talking SED to me. 32 * 33 * The difference between SED and WLC is that SED includes the incoming 34 * job in the cost function (the increment of 1). SED may outperform 35 * WLC, while scheduling big jobs under larger heterogeneous systems 36 * (the server weight varies a lot). 37 * 38 */ 39 40#include <linux/module.h> 41#include <linux/kernel.h> 42 43#include <net/ip_vs.h> 44 45 46static int 47ip_vs_sed_init_svc(struct ip_vs_service *svc) 48{ 49 return 0; 50} 51 52 53static int 54ip_vs_sed_done_svc(struct ip_vs_service *svc) 55{ 56 return 0; 57} 58 59 60static int 61ip_vs_sed_update_svc(struct ip_vs_service *svc) 62{ 63 return 0; 64} 65 66 67static inline unsigned int 68ip_vs_sed_dest_overhead(struct ip_vs_dest *dest) 69{ 70 /* 71 * We only use the active connection number in the cost 72 * calculation here. 73 */ 74 return atomic_read(&dest->activeconns) + 1; 75} 76 77 78/* 79 * Weighted Least Connection scheduling 80 */ 81static struct ip_vs_dest * 82ip_vs_sed_schedule(struct ip_vs_service *svc, const struct sk_buff *skb) 83{ 84 struct ip_vs_dest *dest, *least; 85 unsigned int loh, doh; 86 87 IP_VS_DBG(6, "ip_vs_sed_schedule(): Scheduling...\n"); 88 89 /* 90 * We calculate the load of each dest server as follows: 91 * (server expected overhead) / dest->weight 92 * 93 * Remember -- no floats in kernel mode!!! 94 * The comparison of h1*w2 > h2*w1 is equivalent to that of 95 * h1/w1 > h2/w2 96 * if every weight is larger than zero. 97 * 98 * The server with weight=0 is quiesced and will not receive any 99 * new connections. 100 */ 101 102 list_for_each_entry(dest, &svc->destinations, n_list) { 103 if (!(dest->flags & IP_VS_DEST_F_OVERLOAD) && 104 atomic_read(&dest->weight) > 0) { 105 least = dest; 106 loh = ip_vs_sed_dest_overhead(least); 107 goto nextstage; 108 } 109 } 110 return NULL; 111 112 /* 113 * Find the destination with the least load. 114 */ 115 nextstage: 116 list_for_each_entry_continue(dest, &svc->destinations, n_list) { 117 if (dest->flags & IP_VS_DEST_F_OVERLOAD) 118 continue; 119 doh = ip_vs_sed_dest_overhead(dest); 120 if (loh * atomic_read(&dest->weight) > 121 doh * atomic_read(&least->weight)) { 122 least = dest; 123 loh = doh; 124 } 125 } 126 127 IP_VS_DBG(6, "SED: server %u.%u.%u.%u:%u " 128 "activeconns %d refcnt %d weight %d overhead %d\n", 129 NIPQUAD(least->addr), ntohs(least->port), 130 atomic_read(&least->activeconns), 131 atomic_read(&least->refcnt), 132 atomic_read(&least->weight), loh); 133 134 return least; 135} 136 137 138static struct ip_vs_scheduler ip_vs_sed_scheduler = 139{ 140 .name = "sed", 141 .refcnt = ATOMIC_INIT(0), 142 .module = THIS_MODULE, 143 .init_service = ip_vs_sed_init_svc, 144 .done_service = ip_vs_sed_done_svc, 145 .update_service = ip_vs_sed_update_svc, 146 .schedule = ip_vs_sed_schedule, 147}; 148 149 150static int __init ip_vs_sed_init(void) 151{ 152 INIT_LIST_HEAD(&ip_vs_sed_scheduler.n_list); 153 return register_ip_vs_scheduler(&ip_vs_sed_scheduler); 154} 155 156static void __exit ip_vs_sed_cleanup(void) 157{ 158 unregister_ip_vs_scheduler(&ip_vs_sed_scheduler); 159} 160 161module_init(ip_vs_sed_init); 162module_exit(ip_vs_sed_cleanup); 163MODULE_LICENSE("GPL"); 164