net/ipv4/ipvs/ip_vs_sed.c

   1 /*
   2  * IPVS:        Shortest Expected Delay scheduling module
   3  *
   4  * Version:     $Id: ip_vs_sed.c,v 1.1 2003/05/10 03:06:08 wensong 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 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
  46 static int
  47 ip_vs_sed_init_svc(struct ip_vs_service *svc)
  48 {
  49         return 0;
  50 }
  51
  52
  53 static int
  54 ip_vs_sed_done_svc(struct ip_vs_service *svc)
  55 {
  56         return 0;
  57 }
  58
  59
  60 static int
  61 ip_vs_sed_update_svc(struct ip_vs_service *svc)
  62 {
  63         return 0;
  64 }
  65
  66
  67 static inline unsigned int
  68 ip_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  */
  81 static struct ip_vs_dest *
  82 ip_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
 138 static 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
 150 static 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
 156 static void __exit ip_vs_sed_cleanup(void)
 157 {
 158         unregister_ip_vs_scheduler(&ip_vs_sed_scheduler);
 159 }
 160
 161 module_init(ip_vs_sed_init);
 162 module_exit(ip_vs_sed_cleanup);
 163 MODULE_LICENSE("GPL");