// SPDX-License-Identifier: GPL-2.0-or-later
/*
* IPVS: Shortest Expected Delay scheduling module
*
* Authors: Wensong Zhang <[email protected]>
*
* Changes:
*/
/*
* The SED algorithm attempts to minimize each job's expected delay until
* completion. The expected delay that the job will experience is
* (Ci + 1) / Ui if sent to the ith server, in which Ci is the number of
* jobs on the ith server and Ui is the fixed service rate (weight) of
* the ith server. The SED algorithm adopts a greedy policy that each does
* what is in its own best interest, i.e. to join the queue which would
* minimize its expected delay of completion.
*
* 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 SED to me.
*
* The difference between SED and WLC is that SED includes the incoming
* job in the cost function (the increment of 1). SED may outperform
* WLC, while scheduling big jobs under larger heterogeneous systems
* (the server weight varies a lot).
*
*/
#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_sed_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_sed_schedule(struct ip_vs_service *svc, const struct sk_buff *skb,
struct ip_vs_iphdr *iph)
{
struct ip_vs_dest *dest, *least;
int loh, 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) > 0) {
least = dest;
loh = ip_vs_sed_dest_overhead(least);
goto nextstage;
}
}
ip_vs_scheduler_err(svc, "no destination available");
return NULL;
/*
* Find the destination with the least load.
*/
nextstage:
list_for_each_entry_continue_rcu(dest, &svc->destinations, n_list) {
if (dest->flags & IP_VS_DEST_F_OVERLOAD)
continue;
doh = ip_vs_sed_dest_overhead(dest);
if ((__s64)loh * atomic_read(&dest->weight) >
(__s64)doh * atomic_read(&least->weight)) {
least = dest;
loh = doh;
}
}
IP_VS_DBG_BUF(6, "SED: 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),
refcount_read(&least->refcnt),
atomic_read(&least->weight), loh);
return least;
}
static struct ip_vs_scheduler ip_vs_sed_scheduler =
{
.name = "sed",
.refcnt = ATOMIC_INIT(0),
.module = THIS_MODULE,
.n_list = LIST_HEAD_INIT(ip_vs_sed_scheduler.n_list),
.schedule = ip_vs_sed_schedule,
};
static int __init ip_vs_sed_init(void)
{
return register_ip_vs_scheduler(&ip_vs_sed_scheduler);
}
static void __exit ip_vs_sed_cleanup(void)
{
unregister_ip_vs_scheduler(&ip_vs_sed_scheduler);
synchronize_rcu();
}
module_init(ip_vs_sed_init);
module_exit(ip_vs_sed_cleanup);
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("ipvs shortest expected delay scheduler");
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