LXR linux/net/netfilter/ipvs/ip_vs

   1// SPDX-License-Identifier: GPL-2.0-or-later
   2/* IPVS:        Power of Twos Choice Scheduling module
   3 *
   4 * Authors:     Darby Payne <darby.payne@applovin.com>
   5 */
   6
   7#define KMSG_COMPONENT "IPVS"
   8#define pr_fmt(fmt) KMSG_COMPONENT ": " fmt
   9
  10#include <linux/kernel.h>
  11#include <linux/module.h>
  12#include <linux/random.h>
  13
  14#include <net/ip_vs.h>
  15
  16/*    Power of Twos Choice scheduling, algorithm originally described by
  17 *    Michael Mitzenmacher.
  18 *
  19 *    Randomly picks two destinations and picks the one with the least
  20 *    amount of connections
  21 *
  22 *    The algorithm calculates a few variables
  23 *    - total_weight = sum of all weights
  24 *    - rweight1 = random number between [0,total_weight]
  25 *    - rweight2 = random number between [0,total_weight]
  26 *
  27 *    For each destination
  28 *      decrement rweight1 and rweight2 by the destination weight
  29 *      pick choice1 when rweight1 is <= 0
  30 *      pick choice2 when rweight2 is <= 0
  31 *
  32 *    Return choice2 if choice2 has less connections than choice 1 normalized
  33 *    by weight
  34 *
  35 * References
  36 * ----------
  37 *
  38 * [Mitzenmacher 2016]
  39 *    The Power of Two Random Choices: A Survey of Techniques and Results
  40 *    Michael Mitzenmacher, Andrea W. Richa y, Ramesh Sitaraman
  41 *    http://www.eecs.harvard.edu/~michaelm/NEWWORK/postscripts/twosurvey.pdf
  42 *
  43 */
  44static struct ip_vs_dest *ip_vs_twos_schedule(struct ip_vs_service *svc,
  45                                              const struct sk_buff *skb,
  46                                              struct ip_vs_iphdr *iph)
  47{
  48        struct ip_vs_dest *dest, *choice1 = NULL, *choice2 = NULL;
  49        int rweight1, rweight2, weight1 = -1, weight2 = -1, overhead1 = 0;
  50        int overhead2, total_weight = 0, weight;
  51
  52        IP_VS_DBG(6, "%s(): Scheduling...\n", __func__);
  53
  54        /* Generate a random weight between [0,sum of all weights) */
  55        list_for_each_entry_rcu(dest, &svc->destinations, n_list) {
  56                if (!(dest->flags & IP_VS_DEST_F_OVERLOAD)) {
  57                        weight = atomic_read(&dest->weight);
  58                        if (weight > 0) {
  59                                total_weight += weight;
  60                                choice1 = dest;
  61                        }
  62                }
  63        }
  64
  65        if (!choice1) {
  66                ip_vs_scheduler_err(svc, "no destination available");
  67                return NULL;
  68        }
  69
  70        /* Add 1 to total_weight so that the random weights are inclusive
  71         * from 0 to total_weight
  72         */
  73        total_weight += 1;
  74        rweight1 = prandom_u32() % total_weight;
  75        rweight2 = prandom_u32() % total_weight;
  76
  77        /* Pick two weighted servers */
  78        list_for_each_entry_rcu(dest, &svc->destinations, n_list) {
  79                if (dest->flags & IP_VS_DEST_F_OVERLOAD)
  80                        continue;
  81
  82                weight = atomic_read(&dest->weight);
  83                if (weight <= 0)
  84                        continue;
  85
  86                rweight1 -= weight;
  87                rweight2 -= weight;
  88
  89                if (rweight1 <= 0 && weight1 == -1) {
  90                        choice1 = dest;
  91                        weight1 = weight;
  92                        overhead1 = ip_vs_dest_conn_overhead(dest);
  93                }
  94
  95                if (rweight2 <= 0 && weight2 == -1) {
  96                        choice2 = dest;
  97                        weight2 = weight;
  98                        overhead2 = ip_vs_dest_conn_overhead(dest);
  99                }
 100
 101                if (weight1 != -1 && weight2 != -1)
 102                        goto nextstage;
 103        }
 104
 105nextstage:
 106        if (choice2 && (weight2 * overhead1) > (weight1 * overhead2))
 107                choice1 = choice2;
 108
 109        IP_VS_DBG_BUF(6, "twos: server %s:%u conns %d refcnt %d weight %d\n",
 110                      IP_VS_DBG_ADDR(choice1->af, &choice1->addr),
 111                      ntohs(choice1->port), atomic_read(&choice1->activeconns),
 112                      refcount_read(&choice1->refcnt),
 113                      atomic_read(&choice1->weight));
 114
 115        return choice1;
 116}
 117
 118static struct ip_vs_scheduler ip_vs_twos_scheduler = {
 119        .name = "twos",
 120        .refcnt = ATOMIC_INIT(0),
 121        .module = THIS_MODULE,
 122        .n_list = LIST_HEAD_INIT(ip_vs_twos_scheduler.n_list),
 123        .schedule = ip_vs_twos_schedule,
 124};
 125
 126static int __init ip_vs_twos_init(void)
 127{
 128        return register_ip_vs_scheduler(&ip_vs_twos_scheduler);
 129}
 130
 131static void __exit ip_vs_twos_cleanup(void)
 132{
 133        unregister_ip_vs_scheduler(&ip_vs_twos_scheduler);
 134        synchronize_rcu();
 135}
 136
 137module_init(ip_vs_twos_init);
 138module_exit(ip_vs_twos_cleanup);
 139MODULE_LICENSE("GPL");
 140