// SPDX-License-Identifier: GPL-2.0-or-later
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/*
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* IPVS: Shortest Expected Delay scheduling module
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*
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* Authors: Wensong Zhang <wensong@linuxvirtualserver.org>
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*
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* Changes:
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*/
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/*
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* The SED algorithm attempts to minimize each job's expected delay until
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* completion. The expected delay that the job will experience is
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* (Ci + 1) / Ui if sent to the ith server, in which Ci is the number of
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* jobs on the ith server and Ui is the fixed service rate (weight) of
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* the ith server. The SED algorithm adopts a greedy policy that each does
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* what is in its own best interest, i.e. to join the queue which would
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* minimize its expected delay of completion.
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*
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* See the following paper for more information:
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* A. Weinrib and S. Shenker, Greed is not enough: Adaptive load sharing
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* in large heterogeneous systems. In Proceedings IEEE INFOCOM'88,
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* pages 986-994, 1988.
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*
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* Thanks must go to Marko Buuri <marko@buuri.name> for talking SED to me.
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*
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* The difference between SED and WLC is that SED includes the incoming
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* job in the cost function (the increment of 1). SED may outperform
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* WLC, while scheduling big jobs under larger heterogeneous systems
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* (the server weight varies a lot).
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*
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*/
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#define KMSG_COMPONENT "IPVS"
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#define pr_fmt(fmt) KMSG_COMPONENT ": " fmt
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#include <linux/module.h>
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#include <linux/kernel.h>
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#include <net/ip_vs.h>
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static inline int
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ip_vs_sed_dest_overhead(struct ip_vs_dest *dest)
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{
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/*
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* We only use the active connection number in the cost
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* calculation here.
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*/
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return atomic_read(&dest->activeconns) + 1;
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}
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/*
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* Weighted Least Connection scheduling
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*/
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static struct ip_vs_dest *
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ip_vs_sed_schedule(struct ip_vs_service *svc, const struct sk_buff *skb,
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struct ip_vs_iphdr *iph)
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{
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struct ip_vs_dest *dest, *least;
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int loh, doh;
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IP_VS_DBG(6, "%s(): Scheduling...\n", __func__);
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/*
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* We calculate the load of each dest server as follows:
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* (server expected overhead) / dest->weight
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*
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* Remember -- no floats in kernel mode!!!
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* The comparison of h1*w2 > h2*w1 is equivalent to that of
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* h1/w1 > h2/w2
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* if every weight is larger than zero.
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*
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* The server with weight=0 is quiesced and will not receive any
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* new connections.
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*/
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list_for_each_entry_rcu(dest, &svc->destinations, n_list) {
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if (!(dest->flags & IP_VS_DEST_F_OVERLOAD) &&
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atomic_read(&dest->weight) > 0) {
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least = dest;
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loh = ip_vs_sed_dest_overhead(least);
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goto nextstage;
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}
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}
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ip_vs_scheduler_err(svc, "no destination available");
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return NULL;
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/*
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* Find the destination with the least load.
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*/
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nextstage:
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list_for_each_entry_continue_rcu(dest, &svc->destinations, n_list) {
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if (dest->flags & IP_VS_DEST_F_OVERLOAD)
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continue;
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doh = ip_vs_sed_dest_overhead(dest);
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if ((__s64)loh * atomic_read(&dest->weight) >
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(__s64)doh * atomic_read(&least->weight)) {
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least = dest;
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loh = doh;
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}
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}
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IP_VS_DBG_BUF(6, "SED: server %s:%u "
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"activeconns %d refcnt %d weight %d overhead %d\n",
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IP_VS_DBG_ADDR(least->af, &least->addr),
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ntohs(least->port),
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atomic_read(&least->activeconns),
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refcount_read(&least->refcnt),
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atomic_read(&least->weight), loh);
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return least;
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}
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static struct ip_vs_scheduler ip_vs_sed_scheduler =
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{
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.name = "sed",
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.refcnt = ATOMIC_INIT(0),
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.module = THIS_MODULE,
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.n_list = LIST_HEAD_INIT(ip_vs_sed_scheduler.n_list),
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.schedule = ip_vs_sed_schedule,
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};
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static int __init ip_vs_sed_init(void)
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{
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return register_ip_vs_scheduler(&ip_vs_sed_scheduler);
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}
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static void __exit ip_vs_sed_cleanup(void)
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{
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unregister_ip_vs_scheduler(&ip_vs_sed_scheduler);
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synchronize_rcu();
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}
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module_init(ip_vs_sed_init);
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module_exit(ip_vs_sed_cleanup);
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MODULE_LICENSE("GPL");
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