ip_vs_wrr.c

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/*
 * IPVS:        Weighted Round-Robin 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:
 *     Wensong Zhang            :     changed the ip_vs_wrr_schedule to return dest
 *     Wensong Zhang            :     changed some comestics things for debugging
 *     Wensong Zhang            :     changed for the d-linked destination list
 *     Wensong Zhang            :     added the ip_vs_wrr_update_svc
 *     Julian Anastasov         :     fixed the bug of returning destination
 *                                    with weight 0 when all weights are zero
 *
 */

#define KMSG_COMPONENT "IPVS"
#define pr_fmt(fmt) KMSG_COMPONENT ": " fmt

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/net.h>
#include <linux/gcd.h>

#include <net/ip_vs.h>

/*
 * current destination pointer for weighted round-robin scheduling
 */
struct ip_vs_wrr_mark {
    struct list_head *cl;   /* current list head */
    int cw;         /* current weight */
    int mw;         /* maximum weight */
    int di;         /* decreasing interval */
};


static int ip_vs_wrr_gcd_weight(struct ip_vs_service *svc)
{
    struct ip_vs_dest *dest;
    int weight;
    int g = 0;

    list_for_each_entry(dest, &svc->destinations, n_list) {
        weight = atomic_read(&dest->weight);
        if (weight > 0) {
            if (g > 0)
                g = gcd(weight, g);
            else
                g = weight;
        }
    }
    return g ? g : 1;
}


/*
 *    Get the maximum weight of the service destinations.
 */
static int ip_vs_wrr_max_weight(struct ip_vs_service *svc)
{
    struct ip_vs_dest *dest;
    int new_weight, weight = 0;

    list_for_each_entry(dest, &svc->destinations, n_list) {
        new_weight = atomic_read(&dest->weight);
        if (new_weight > weight)
            weight = new_weight;
    }

    return weight;
}


static int ip_vs_wrr_init_svc(struct ip_vs_service *svc)
{
    struct ip_vs_wrr_mark *mark;

    /*
     *    Allocate the mark variable for WRR scheduling
     */
    mark = kmalloc(sizeof(struct ip_vs_wrr_mark), GFP_KERNEL);
    if (mark == NULL)
        return -ENOMEM;

    mark->cl = &svc->destinations;
    mark->cw = 0;
    mark->mw = ip_vs_wrr_max_weight(svc);
    mark->di = ip_vs_wrr_gcd_weight(svc);
    svc->sched_data = mark;

    return 0;
}


static int ip_vs_wrr_done_svc(struct ip_vs_service *svc)
{
    /*
     *    Release the mark variable
     */
    kfree(svc->sched_data);

    return 0;
}


static int ip_vs_wrr_update_svc(struct ip_vs_service *svc)
{
    struct ip_vs_wrr_mark *mark = svc->sched_data;

    mark->cl = &svc->destinations;
    mark->mw = ip_vs_wrr_max_weight(svc);
    mark->di = ip_vs_wrr_gcd_weight(svc);
    if (mark->cw > mark->mw)
        mark->cw = 0;
    return 0;
}


/*
 *    Weighted Round-Robin Scheduling
 */
static struct ip_vs_dest *
ip_vs_wrr_schedule(struct ip_vs_service *svc, const struct sk_buff *skb)
{
    struct ip_vs_dest *dest;
    struct ip_vs_wrr_mark *mark = svc->sched_data;
    struct list_head *p;

    IP_VS_DBG(6, "%s(): Scheduling...\n", __func__);

    /*
     * This loop will always terminate, because mark->cw in (0, max_weight]
     * and at least one server has its weight equal to max_weight.
     */
    write_lock(&svc->sched_lock);
    p = mark->cl;
    while (1) {
        if (mark->cl == &svc->destinations) {
            /* it is at the head of the destination list */

            if (mark->cl == mark->cl->next) {
                /* no dest entry */
                ip_vs_scheduler_err(svc,
                    "no destination available: "
                    "no destinations present");
                dest = NULL;
                goto out;
            }

            mark->cl = svc->destinations.next;
            mark->cw -= mark->di;
            if (mark->cw <= 0) {
                mark->cw = mark->mw;
                /*
                 * Still zero, which means no available servers.
                 */
                if (mark->cw == 0) {
                    mark->cl = &svc->destinations;
                    ip_vs_scheduler_err(svc,
                        "no destination available");
                    dest = NULL;
                    goto out;
                }
            }
        } else
            mark->cl = mark->cl->next;

        if (mark->cl != &svc->destinations) {
            /* not at the head of the list */
            dest = list_entry(mark->cl, struct ip_vs_dest, n_list);
            if (!(dest->flags & IP_VS_DEST_F_OVERLOAD) &&
                atomic_read(&dest->weight) >= mark->cw) {
                /* got it */
                break;
            }
        }

        if (mark->cl == p && mark->cw == mark->di) {
            /* back to the start, and no dest is found.
               It is only possible when all dests are OVERLOADED */
            dest = NULL;
            ip_vs_scheduler_err(svc,
                "no destination available: "
                "all destinations are overloaded");
            goto out;
        }
    }

    IP_VS_DBG_BUF(6, "WRR: server %s:%u "
              "activeconns %d refcnt %d weight %d\n",
              IP_VS_DBG_ADDR(svc->af, &dest->addr), ntohs(dest->port),
              atomic_read(&dest->activeconns),
              atomic_read(&dest->refcnt),
              atomic_read(&dest->weight));

  out:
    write_unlock(&svc->sched_lock);
    return dest;
}


static struct ip_vs_scheduler ip_vs_wrr_scheduler = {
    .name =         "wrr",
    .refcnt =       ATOMIC_INIT(0),
    .module =       THIS_MODULE,
    .n_list =       LIST_HEAD_INIT(ip_vs_wrr_scheduler.n_list),
    .init_service =     ip_vs_wrr_init_svc,
    .done_service =     ip_vs_wrr_done_svc,
    .update_service =   ip_vs_wrr_update_svc,
    .schedule =     ip_vs_wrr_schedule,
};

static int __init ip_vs_wrr_init(void)
{
    return register_ip_vs_scheduler(&ip_vs_wrr_scheduler) ;
}

static void __exit ip_vs_wrr_cleanup(void)
{
    unregister_ip_vs_scheduler(&ip_vs_wrr_scheduler);
}

module_init(ip_vs_wrr_init);
module_exit(ip_vs_wrr_cleanup);
MODULE_LICENSE("GPL");