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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.
*
*/
#include <linux/module.h>
#include <linux/kernel.h>
#include <net/ip_vs.h>
static inline unsigned 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_dest *dest, *least = NULL;
unsigned int loh = 0, doh;
IP_VS_DBG(6, "ip_vs_nq_schedule(): Scheduling...\n");
/*
* 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(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 ||
(loh * atomic_read(&dest->weight) >
doh * atomic_read(&least->weight))) {
least = dest;
loh = doh;
}
}
if (!least)
return NULL;
out:
IP_VS_DBG(6, "NQ: server %u.%u.%u.%u:%u "
"activeconns %d refcnt %d weight %d overhead %d\n",
NIPQUAD(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);
}
module_init(ip_vs_nq_init);
module_exit(ip_vs_nq_cleanup);
MODULE_LICENSE("GPL");
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