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- /*
- * IPVS: Never Queue 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 NQ algorithm adopts a two-speed model. When there is an idle server
- * available, the job will be sent to the idle server, instead of waiting
- * for a fast one. When there is no idle server available, the job will be
- * sent to the server that minimize its expected delay (The Shortest
- * Expected Delay scheduling algorithm).
- *
- * 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 NQ to me.
- *
- * The difference between NQ and SED is that NQ can improve overall
- * system utilization.
- *
- */
- #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_nq_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_nq_schedule(struct ip_vs_service *svc, const struct sk_buff *skb,
- struct ip_vs_iphdr *iph)
- {
- struct ip_vs_dest *dest, *least = NULL;
- int loh = 0, 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))
- continue;
- doh = ip_vs_nq_dest_overhead(dest);
- /* return the server directly if it is idle */
- if (atomic_read(&dest->activeconns) == 0) {
- least = dest;
- loh = doh;
- goto out;
- }
- if (!least ||
- ((__s64)loh * atomic_read(&dest->weight) >
- (__s64)doh * atomic_read(&least->weight))) {
- least = dest;
- loh = doh;
- }
- }
- if (!least) {
- ip_vs_scheduler_err(svc, "no destination available");
- return NULL;
- }
- out:
- IP_VS_DBG_BUF(6, "NQ: 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_nq_scheduler =
- {
- .name = "nq",
- .refcnt = ATOMIC_INIT(0),
- .module = THIS_MODULE,
- .n_list = LIST_HEAD_INIT(ip_vs_nq_scheduler.n_list),
- .schedule = ip_vs_nq_schedule,
- };
- static int __init ip_vs_nq_init(void)
- {
- return register_ip_vs_scheduler(&ip_vs_nq_scheduler);
- }
- static void __exit ip_vs_nq_cleanup(void)
- {
- unregister_ip_vs_scheduler(&ip_vs_nq_scheduler);
- synchronize_rcu();
- }
- module_init(ip_vs_nq_init);
- module_exit(ip_vs_nq_cleanup);
- MODULE_LICENSE("GPL");
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