net/ipv4/ipvs/ip_vs_nq.c

   1 /*
   2  * IPVS:        Never Queue scheduling module
   3  *
   4  * Version:     $Id: ip_vs_nq.c,v 1.2 2003/06/08 09:31:19 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 NQ algorithm adopts a two-speed model. When there is an idle server
  19  * available, the job will be sent to the idle server, instead of waiting
  20  * for a fast one. When there is no idle server available, the job will be
  21  * sent to the server that minimize its expected delay (The Shortest
  22  * Expected Delay scheduling algorithm).
  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 NQ to me.
  30  *
  31  * The difference between NQ and SED is that NQ can improve overall
  32  * system utilization.
  33  *
  34  */
  35
  36 #include <linux/module.h>
  37 #include <linux/kernel.h>
  38
  39 #include <net/ip_vs.h>
  40
  41
  42 static int
  43 ip_vs_nq_init_svc(struct ip_vs_service *svc)
  44 {
  45         return 0;
  46 }
  47
  48
  49 static int
  50 ip_vs_nq_done_svc(struct ip_vs_service *svc)
  51 {
  52         return 0;
  53 }
  54
  55
  56 static int
  57 ip_vs_nq_update_svc(struct ip_vs_service *svc)
  58 {
  59         return 0;
  60 }
  61
  62
  63 static inline unsigned int
  64 ip_vs_nq_dest_overhead(struct ip_vs_dest *dest)
  65 {
  66         /*
  67          * We only use the active connection number in the cost
  68          * calculation here.
  69          */
  70         return atomic_read(&dest->activeconns) + 1;
  71 }
  72
  73
  74 /*
  75  *      Weighted Least Connection scheduling
  76  */
  77 static struct ip_vs_dest *
  78 ip_vs_nq_schedule(struct ip_vs_service *svc, const struct sk_buff *skb)
  79 {
  80         struct ip_vs_dest *dest, *least = NULL;
  81         unsigned int loh = 0, doh;
  82
  83         IP_VS_DBG(6, "ip_vs_nq_schedule(): Scheduling...\n");
  84
  85         /*
  86          * We calculate the load of each dest server as follows:
  87          *      (server expected overhead) / dest->weight
  88          *
  89          * Remember -- no floats in kernel mode!!!
  90          * The comparison of h1*w2 > h2*w1 is equivalent to that of
  91          *                h1/w1 > h2/w2
  92          * if every weight is larger than zero.
  93          *
  94          * The server with weight=0 is quiesced and will not receive any
  95          * new connections.
  96          */
  97
  98         list_for_each_entry(dest, &svc->destinations, n_list) {
  99
 100                 if (dest->flags & IP_VS_DEST_F_OVERLOAD ||
 101                     !atomic_read(&dest->weight))
 102                         continue;
 103
 104                 doh = ip_vs_nq_dest_overhead(dest);
 105
 106                 /* return the server directly if it is idle */
 107                 if (atomic_read(&dest->activeconns) == 0) {
 108                         least = dest;
 109                         loh = doh;
 110                         goto out;
 111                 }
 112
 113                 if (!least ||
 114                     (loh * atomic_read(&dest->weight) >
 115                      doh * atomic_read(&least->weight))) {
 116                         least = dest;
 117                         loh = doh;
 118                 }
 119         }
 120
 121         if (!least)
 122                 return NULL;
 123
 124   out:
 125         IP_VS_DBG(6, "NQ: server %u.%u.%u.%u:%u "
 126                   "activeconns %d refcnt %d weight %d overhead %d\n",
 127                   NIPQUAD(least->addr), ntohs(least->port),
 128                   atomic_read(&least->activeconns),
 129                   atomic_read(&least->refcnt),
 130                   atomic_read(&least->weight), loh);
 131
 132         return least;
 133 }
 134
 135
 136 static struct ip_vs_scheduler ip_vs_nq_scheduler =
 137 {
 138         .name =                 "nq",
 139         .refcnt =               ATOMIC_INIT(0),
 140         .module =               THIS_MODULE,
 141         .init_service =         ip_vs_nq_init_svc,
 142         .done_service =         ip_vs_nq_done_svc,
 143         .update_service =       ip_vs_nq_update_svc,
 144         .schedule =             ip_vs_nq_schedule,
 145 };
 146
 147
 148 static int __init ip_vs_nq_init(void)
 149 {
 150         INIT_LIST_HEAD(&ip_vs_nq_scheduler.n_list);
 151         return register_ip_vs_scheduler(&ip_vs_nq_scheduler);
 152 }
 153
 154 static void __exit ip_vs_nq_cleanup(void)
 155 {
 156         unregister_ip_vs_scheduler(&ip_vs_nq_scheduler);
 157 }
 158
 159 module_init(ip_vs_nq_init);
 160 module_exit(ip_vs_nq_cleanup);
 161 MODULE_LICENSE("GPL");