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