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phoenix |
/*
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* IPVS: Shortest Expected Delay scheduling module
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*
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* Version: $Id: ip_vs_sed.c,v 1.1.1.1 2004-04-15 01:14:05 phoenix Exp $
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*
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* Authors: Wensong Zhang <wensong@linuxvirtualserver.org>
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version
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* 2 of the License, or (at your option) any later version.
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*
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* Changes:
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*
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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 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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#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 int
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ip_vs_sed_init_svc(struct ip_vs_service *svc)
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{
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return 0;
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}
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static int
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ip_vs_sed_done_svc(struct ip_vs_service *svc)
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{
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return 0;
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}
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static int
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ip_vs_sed_update_svc(struct ip_vs_service *svc)
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{
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return 0;
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}
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static inline unsigned 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, struct iphdr *iph)
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{
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register struct list_head *l, *e;
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struct ip_vs_dest *dest, *least;
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unsigned int loh, doh;
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IP_VS_DBG(6, "ip_vs_sed_schedule(): Scheduling...\n");
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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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l = &svc->destinations;
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for (e=l->next; e!=l; e=e->next) {
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least = list_entry(e, struct ip_vs_dest, n_list);
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if (atomic_read(&least->weight) > 0) {
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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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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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for (e=e->next; e!=l; e=e->next) {
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dest = list_entry(e, struct ip_vs_dest, n_list);
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doh = ip_vs_sed_dest_overhead(dest);
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if (loh * atomic_read(&dest->weight) >
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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(6, "SED: server %u.%u.%u.%u:%u "
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"activeconns %d refcnt %d weight %d overhead %d\n",
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NIPQUAD(least->addr), ntohs(least->port),
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atomic_read(&least->activeconns),
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atomic_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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.init_service = ip_vs_sed_init_svc,
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.done_service = ip_vs_sed_done_svc,
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.update_service = ip_vs_sed_update_svc,
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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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INIT_LIST_HEAD(&ip_vs_sed_scheduler.n_list);
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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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}
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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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