ip_vs_nq.c

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/*
 * IPVS:        Never Queue scheduling module
 *
 * Authors:     Wensong Zhang <[email protected]>
 *
 *              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 <[email protected]> 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 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, "%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(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) {
        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(svc->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);
}

module_init(ip_vs_nq_init);
module_exit(ip_vs_nq_cleanup);
MODULE_LICENSE("GPL");