net/netfilter/ipvs/ip_vs_nq.c

   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(svc->af, &least->addr), ntohs(least->port),
 111                       atomic_read(&least->activeconns),
 112                       atomic_read(&least->refcnt),
 113                       atomic_read(&least->weight), loh);
 114
 115         return least;
 116 }
 117
 118
 119 static struct ip_vs_scheduler ip_vs_nq_scheduler =
 120 {
 121         .name =                 "nq",
 122         .refcnt =               ATOMIC_INIT(0),
 123         .module =               THIS_MODULE,
 124         .n_list =               LIST_HEAD_INIT(ip_vs_nq_scheduler.n_list),
 125         .schedule =             ip_vs_nq_schedule,
 126 };
 127
 128
 129 static int __init ip_vs_nq_init(void)
 130 {
 131         return register_ip_vs_scheduler(&ip_vs_nq_scheduler);
 132 }
 133
 134 static void __exit ip_vs_nq_cleanup(void)
 135 {
 136         unregister_ip_vs_scheduler(&ip_vs_nq_scheduler);
 137         synchronize_rcu();
 138 }
 139
 140 module_init(ip_vs_nq_init);
 141 module_exit(ip_vs_nq_cleanup);
 142 MODULE_LICENSE("GPL");