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/net/netfilter/ipvs/ip_vs_sed.c

http://github.com/mirrors/linux
C | 139 lines | 67 code | 20 blank | 52 comment | 3 complexity | 2953815bcb01b5bef66f05cceae72f72 MD5 | raw file
  1// SPDX-License-Identifier: GPL-2.0-or-later
  2/*
  3 * IPVS:        Shortest Expected Delay scheduling module
  4 *
  5 * Authors:     Wensong Zhang <wensong@linuxvirtualserver.org>
  6 *
  7 * Changes:
  8 */
  9
 10/*
 11 * The SED algorithm attempts to minimize each job's expected delay until
 12 * completion. The expected delay that the job will experience is
 13 * (Ci + 1) / Ui if sent to the ith server, in which Ci is the number of
 14 * jobs on the ith server and Ui is the fixed service rate (weight) of
 15 * the ith server. The SED algorithm adopts a greedy policy that each does
 16 * what is in its own best interest, i.e. to join the queue which would
 17 * minimize its expected delay of completion.
 18 *
 19 * See the following paper for more information:
 20 * A. Weinrib and S. Shenker, Greed is not enough: Adaptive load sharing
 21 * in large heterogeneous systems. In Proceedings IEEE INFOCOM'88,
 22 * pages 986-994, 1988.
 23 *
 24 * Thanks must go to Marko Buuri <marko@buuri.name> for talking SED to me.
 25 *
 26 * The difference between SED and WLC is that SED includes the incoming
 27 * job in the cost function (the increment of 1). SED may outperform
 28 * WLC, while scheduling big jobs under larger heterogeneous systems
 29 * (the server weight varies a lot).
 30 *
 31 */
 32
 33#define KMSG_COMPONENT "IPVS"
 34#define pr_fmt(fmt) KMSG_COMPONENT ": " fmt
 35
 36#include <linux/module.h>
 37#include <linux/kernel.h>
 38
 39#include <net/ip_vs.h>
 40
 41
 42static inline int
 43ip_vs_sed_dest_overhead(struct ip_vs_dest *dest)
 44{
 45	/*
 46	 * We only use the active connection number in the cost
 47	 * calculation here.
 48	 */
 49	return atomic_read(&dest->activeconns) + 1;
 50}
 51
 52
 53/*
 54 *	Weighted Least Connection scheduling
 55 */
 56static struct ip_vs_dest *
 57ip_vs_sed_schedule(struct ip_vs_service *svc, const struct sk_buff *skb,
 58		   struct ip_vs_iphdr *iph)
 59{
 60	struct ip_vs_dest *dest, *least;
 61	int loh, 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_rcu(dest, &svc->destinations, n_list) {
 79		if (!(dest->flags & IP_VS_DEST_F_OVERLOAD) &&
 80		    atomic_read(&dest->weight) > 0) {
 81			least = dest;
 82			loh = ip_vs_sed_dest_overhead(least);
 83			goto nextstage;
 84		}
 85	}
 86	ip_vs_scheduler_err(svc, "no destination available");
 87	return NULL;
 88
 89	/*
 90	 *    Find the destination with the least load.
 91	 */
 92  nextstage:
 93	list_for_each_entry_continue_rcu(dest, &svc->destinations, n_list) {
 94		if (dest->flags & IP_VS_DEST_F_OVERLOAD)
 95			continue;
 96		doh = ip_vs_sed_dest_overhead(dest);
 97		if ((__s64)loh * atomic_read(&dest->weight) >
 98		    (__s64)doh * atomic_read(&least->weight)) {
 99			least = dest;
100			loh = doh;
101		}
102	}
103
104	IP_VS_DBG_BUF(6, "SED: server %s:%u "
105		      "activeconns %d refcnt %d weight %d overhead %d\n",
106		      IP_VS_DBG_ADDR(least->af, &least->addr),
107		      ntohs(least->port),
108		      atomic_read(&least->activeconns),
109		      refcount_read(&least->refcnt),
110		      atomic_read(&least->weight), loh);
111
112	return least;
113}
114
115
116static struct ip_vs_scheduler ip_vs_sed_scheduler =
117{
118	.name =			"sed",
119	.refcnt =		ATOMIC_INIT(0),
120	.module =		THIS_MODULE,
121	.n_list =		LIST_HEAD_INIT(ip_vs_sed_scheduler.n_list),
122	.schedule =		ip_vs_sed_schedule,
123};
124
125
126static int __init ip_vs_sed_init(void)
127{
128	return register_ip_vs_scheduler(&ip_vs_sed_scheduler);
129}
130
131static void __exit ip_vs_sed_cleanup(void)
132{
133	unregister_ip_vs_scheduler(&ip_vs_sed_scheduler);
134	synchronize_rcu();
135}
136
137module_init(ip_vs_sed_init);
138module_exit(ip_vs_sed_cleanup);
139MODULE_LICENSE("GPL");