1 // SPDX-License-Identifier: GPL-2.0-or-later 2 /* 3 * IPVS: Never Queue scheduling module 4 * 5 * Authors: Wensong Zhang <wensong@linuxvirtualserver.org> 6 * 7 * Changes: 8 */ 9 10 /* 11 * The NQ algorithm adopts a two-speed model. When there is an idle server 12 * available, the job will be sent to the idle server, instead of waiting 13 * for a fast one. When there is no idle server available, the job will be 14 * sent to the server that minimize its expected delay (The Shortest 15 * Expected Delay scheduling algorithm). 16 * 17 * See the following paper for more information: 18 * A. Weinrib and S. Shenker, Greed is not enough: Adaptive load sharing 19 * in large heterogeneous systems. In Proceedings IEEE INFOCOM'88, 20 * pages 986-994, 1988. 21 * 22 * Thanks must go to Marko Buuri <marko@buuri.name> for talking NQ to me. 23 * 24 * The difference between NQ and SED is that NQ can improve overall 25 * system utilization. 26 * 27 */ 28 29 #define KMSG_COMPONENT "IPVS" 30 #define pr_fmt(fmt) KMSG_COMPONENT ": " fmt 31 32 #include <linux/module.h> 33 #include <linux/kernel.h> 34 35 #include <net/ip_vs.h> 36 37 38 static inline int 39 ip_vs_nq_dest_overhead(struct ip_vs_dest *dest) 40 { 41 /* 42 * We only use the active connection number in the cost 43 * calculation here. 44 */ 45 return atomic_read(&dest->activeconns) + 1; 46 } 47 48 49 /* 50 * Weighted Least Connection scheduling 51 */ 52 static struct ip_vs_dest * 53 ip_vs_nq_schedule(struct ip_vs_service *svc, const struct sk_buff *skb, 54 struct ip_vs_iphdr *iph) 55 { 56 struct ip_vs_dest *dest, *least = NULL; 57 int loh = 0, doh; 58 59 IP_VS_DBG(6, "%s(): Scheduling...\n", __func__); 60 61 /* 62 * We calculate the load of each dest server as follows: 63 * (server expected overhead) / dest->weight 64 * 65 * Remember -- no floats in kernel mode!!! 66 * The comparison of h1*w2 > h2*w1 is equivalent to that of 67 * h1/w1 > h2/w2 68 * if every weight is larger than zero. 69 * 70 * The server with weight=0 is quiesced and will not receive any 71 * new connections. 72 */ 73 74 list_for_each_entry_rcu(dest, &svc->destinations, n_list) { 75 76 if (dest->flags & IP_VS_DEST_F_OVERLOAD || 77 !atomic_read(&dest->weight)) 78 continue; 79 80 doh = ip_vs_nq_dest_overhead(dest); 81 82 /* return the server directly if it is idle */ 83 if (atomic_read(&dest->activeconns) == 0) { 84 least = dest; 85 loh = doh; 86 goto out; 87 } 88 89 if (!least || 90 ((__s64)loh * atomic_read(&dest->weight) > 91 (__s64)doh * atomic_read(&least->weight))) { 92 least = dest; 93 loh = doh; 94 } 95 } 96 97 if (!least) { 98 ip_vs_scheduler_err(svc, "no destination available"); 99 return NULL; 100 } 101 102 out: 103 IP_VS_DBG_BUF(6, "NQ: server %s:%u " 104 "activeconns %d refcnt %d weight %d overhead %d\n", 105 IP_VS_DBG_ADDR(least->af, &least->addr), 106 ntohs(least->port), 107 atomic_read(&least->activeconns), 108 refcount_read(&least->refcnt), 109 atomic_read(&least->weight), loh); 110 111 return least; 112 } 113 114 115 static struct ip_vs_scheduler ip_vs_nq_scheduler = 116 { 117 .name = "nq", 118 .refcnt = ATOMIC_INIT(0), 119 .module = THIS_MODULE, 120 .n_list = LIST_HEAD_INIT(ip_vs_nq_scheduler.n_list), 121 .schedule = ip_vs_nq_schedule, 122 }; 123 124 125 static int __init ip_vs_nq_init(void) 126 { 127 return register_ip_vs_scheduler(&ip_vs_nq_scheduler); 128 } 129 130 static void __exit ip_vs_nq_cleanup(void) 131 { 132 unregister_ip_vs_scheduler(&ip_vs_nq_scheduler); 133 synchronize_rcu(); 134 } 135 136 module_init(ip_vs_nq_init); 137 module_exit(ip_vs_nq_cleanup); 138 MODULE_LICENSE("GPL"); 139 MODULE_DESCRIPTION("ipvs never queue scheduler"); 140