// SPDX-License-Identifier: GPL-2.0-or-later
/*
* IPVS: Weighted Round-Robin Scheduling module
*
* Authors: Wensong Zhang <[email protected]>
*
* 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>
/* The WRR algorithm depends on some caclulations:
* - mw: maximum weight
* - di: weight step, greatest common divisor from all weights
* - cw: current required weight
* As result, all weights are in the [di..mw] range with a step=di.
*
* First, we start with cw = mw and select dests with weight >= cw.
* Then cw is reduced with di and all dests are checked again.
* Last pass should be with cw = di. We have mw/di passes in total:
*
* pass 1: cw = max weight
* pass 2: cw = max weight - di
* pass 3: cw = max weight - 2 * di
* ...
* last pass: cw = di
*
* Weights are supposed to be >= di but we run in parallel with
* weight changes, it is possible some dest weight to be reduced
* below di, bad if it is the only available dest.
*
* So, we modify how mw is calculated, now it is reduced with (di - 1),
* so that last cw is 1 to catch such dests with weight below di:
* pass 1: cw = max weight - (di - 1)
* pass 2: cw = max weight - di - (di - 1)
* pass 3: cw = max weight - 2 * di - (di - 1)
* ...
* last pass: cw = 1
*
*/
/*
* current destination pointer for weighted round-robin scheduling
*/
struct ip_vs_wrr_mark {
struct ip_vs_dest *cl; /* current dest or head */
int cw; /* current weight */
int mw; /* maximum weight */
int di; /* decreasing interval */
struct rcu_head rcu_head;
};
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 = list_entry(&svc->destinations, struct ip_vs_dest, n_list);
mark->di = ip_vs_wrr_gcd_weight(svc);
mark->mw = ip_vs_wrr_max_weight(svc) - (mark->di - 1);
mark->cw = mark->mw;
svc->sched_data = mark;
return 0;
}
static void ip_vs_wrr_done_svc(struct ip_vs_service *svc)
{
struct ip_vs_wrr_mark *mark = svc->sched_data;
/*
* Release the mark variable
*/
kfree_rcu(mark, rcu_head);
}
static int ip_vs_wrr_dest_changed(struct ip_vs_service *svc,
struct ip_vs_dest *dest)
{
struct ip_vs_wrr_mark *mark = svc->sched_data;
spin_lock_bh(&svc->sched_lock);
mark->cl = list_entry(&svc->destinations, struct ip_vs_dest, n_list);
mark->di = ip_vs_wrr_gcd_weight(svc);
mark->mw = ip_vs_wrr_max_weight(svc) - (mark->di - 1);
if (mark->cw > mark->mw || !mark->cw)
mark->cw = mark->mw;
else if (mark->di > 1)
mark->cw = (mark->cw / mark->di) * mark->di + 1;
spin_unlock_bh(&svc->sched_lock);
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_iphdr *iph)
{
struct ip_vs_dest *dest, *last, *stop = NULL;
struct ip_vs_wrr_mark *mark = svc->sched_data;
bool last_pass = false, restarted = false;
IP_VS_DBG(6, "%s(): Scheduling...\n", __func__);
spin_lock_bh(&svc->sched_lock);
dest = mark->cl;
/* No available dests? */
if (mark->mw == 0)
goto err_noavail;
last = dest;
/* Stop only after all dests were checked for weight >= 1 (last pass) */
while (1) {
list_for_each_entry_continue_rcu(dest,
&svc->destinations,
n_list) {
if (!(dest->flags & IP_VS_DEST_F_OVERLOAD) &&
atomic_read(&dest->weight) >= mark->cw)
goto found;
if (dest == stop)
goto err_over;
}
mark->cw -= mark->di;
if (mark->cw <= 0) {
mark->cw = mark->mw;
/* Stop if we tried last pass from first dest:
* 1. last_pass: we started checks when cw > di but
* then all dests were checked for w >= 1
* 2. last was head: the first and only traversal
* was for weight >= 1, for all dests.
*/
if (last_pass ||
&last->n_list == &svc->destinations)
goto err_over;
restarted = true;
}
last_pass = mark->cw <= mark->di;
if (last_pass && restarted &&
&last->n_list != &svc->destinations) {
/* First traversal was for w >= 1 but only
* for dests after 'last', now do the same
* for all dests up to 'last'.
*/
stop = last;
}
}
found:
IP_VS_DBG_BUF(6, "WRR: server %s:%u "
"activeconns %d refcnt %d weight %d\n",
IP_VS_DBG_ADDR(dest->af, &dest->addr), ntohs(dest->port),
atomic_read(&dest->activeconns),
refcount_read(&dest->refcnt),
atomic_read(&dest->weight));
mark->cl = dest;
out:
spin_unlock_bh(&svc->sched_lock);
return dest;
err_noavail:
mark->cl = dest;
dest = NULL;
ip_vs_scheduler_err(svc, "no destination available");
goto out;
err_over:
mark->cl = dest;
dest = NULL;
ip_vs_scheduler_err(svc, "no destination available: "
"all destinations are overloaded");
goto out;
}
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,
.add_dest = ip_vs_wrr_dest_changed,
.del_dest = ip_vs_wrr_dest_changed,
.upd_dest = ip_vs_wrr_dest_changed,
.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);
synchronize_rcu();
}
module_init(ip_vs_wrr_init);
module_exit(ip_vs_wrr_cleanup);
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("ipvs weighted round-robin scheduler");
Codebase Browser
linux