LXR linux/net/netfilter/ipvs/ip_vs

   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
  43static inline unsigned int
  44ip_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 */
  57static struct ip_vs_dest *
  58ip_vs_nq_schedule(struct ip_vs_service *svc, const struct sk_buff *skb)
  59{
  60        struct ip_vs_dest *dest, *least = NULL;
  61        unsigned int loh = 0, doh;
  62
  63        IP_VS_DBG(6, "%s(): Scheduling...\n", __func__);
  64
  65        /*
  66         * We calculate the load of each dest server as follows:
  67         *      (server expected overhead) / dest->weight
  68         *
  69         * Remember -- no floats in kernel mode!!!
  70         * The comparison of h1*w2 > h2*w1 is equivalent to that of
  71         *                h1/w1 > h2/w2
  72         * if every weight is larger than zero.
  73         *
  74         * The server with weight=0 is quiesced and will not receive any
  75         * new connections.
  76         */
  77
  78        list_for_each_entry(dest, &svc->destinations, n_list) {
  79
  80                if (dest->flags & IP_VS_DEST_F_OVERLOAD ||
  81                    !atomic_read(&dest->weight))
  82                        continue;
  83
  84                doh = ip_vs_nq_dest_overhead(dest);
  85
  86                /* return the server directly if it is idle */
  87                if (atomic_read(&dest->activeconns) == 0) {
  88                        least = dest;
  89                        loh = doh;
  90                        goto out;
  91                }
  92
  93                if (!least ||
  94                    (loh * atomic_read(&dest->weight) >
  95                     doh * atomic_read(&least->weight))) {
  96                        least = dest;
  97                        loh = doh;
  98                }
  99        }
 100
 101        if (!least) {
 102                IP_VS_ERR_RL("NQ: no destination available\n");
 103                return NULL;
 104        }
 105
 106  out:
 107        IP_VS_DBG_BUF(6, "NQ: server %s:%u "
 108                      "activeconns %d refcnt %d weight %d overhead %d\n",
 109                      IP_VS_DBG_ADDR(svc->af, &least->addr), ntohs(least->port),
 110                      atomic_read(&least->activeconns),
 111                      atomic_read(&least->refcnt),
 112                      atomic_read(&least->weight), loh);
 113
 114        return least;
 115}
 116
 117
 118static struct ip_vs_scheduler ip_vs_nq_scheduler =
 119{
 120        .name =                 "nq",
 121        .refcnt =               ATOMIC_INIT(0),
 122        .module =               THIS_MODULE,
 123        .n_list =               LIST_HEAD_INIT(ip_vs_nq_scheduler.n_list),
 124        .schedule =             ip_vs_nq_schedule,
 125};
 126
 127
 128static int __init ip_vs_nq_init(void)
 129{
 130        return register_ip_vs_scheduler(&ip_vs_nq_scheduler);
 131}
 132
 133static void __exit ip_vs_nq_cleanup(void)
 134{
 135        unregister_ip_vs_scheduler(&ip_vs_nq_scheduler);
 136}
 137
 138module_init(ip_vs_nq_init);
 139module_exit(ip_vs_nq_cleanup);
 140MODULE_LICENSE("GPL");
 141