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/*
* First Available Server load balancing algorithm.
*
* This file implements an algorithm which emerged during a discussion with
* Steen Larsen, initially inspired from Anshul Gandhi et.al.'s work now
* described as "packing" in section 3.5:
*
* http://reports-archive.adm.cs.cmu.edu/anon/2012/CMU-CS-12-109.pdf
*
* Copyright 2000-2012 Willy Tarreau <w@1wt.eu>
*
* 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.
*
*/
#include <haproxy/api.h>
#include <import/eb32tree.h>
#include <types/server.h>
#include <proto/backend.h>
#include <proto/queue.h>
/* Remove a server from a tree. It must have previously been dequeued. This
* function is meant to be called when a server is going down or has its
* weight disabled.
*
* The server's lock and the lbprm's lock must be held.
*/
static inline void fas_remove_from_tree(struct server *s)
{
s->lb_tree = NULL;
}
/* simply removes a server from a tree.
*
* The server's lock and the lbprm's lock must be held.
*/
static inline void fas_dequeue_srv(struct server *s)
{
eb32_delete(&s->lb_node);
}
/* Queue a server in its associated tree, assuming the weight is >0.
* Servers are sorted by unique ID so that we send all connections to the first
* available server in declaration order (or ID order) until its maxconn is
* reached. It is important to understand that the server weight is not used
* here.
*
* The server's lock and the lbprm's lock must be held.
*/
static inline void fas_queue_srv(struct server *s)
{
s->lb_node.key = s->puid;
eb32_insert(s->lb_tree, &s->lb_node);
}
/* Re-position the server in the FS tree after it has been assigned one
* connection or after it has released one. Note that it is possible that
* the server has been moved out of the tree due to failed health-checks.
*
* The server's lock must be held. The lbprm's lock will be used.
*/
static void fas_srv_reposition(struct server *s)
{
HA_SPIN_LOCK(LBPRM_LOCK, &s->proxy->lbprm.lock);
if (s->lb_tree) {
fas_dequeue_srv(s);
fas_queue_srv(s);
}
HA_SPIN_UNLOCK(LBPRM_LOCK, &s->proxy->lbprm.lock);
}
/* This function updates the server trees according to server <srv>'s new
* state. It should be called when server <srv>'s status changes to down.
* It is not important whether the server was already down or not. It is not
* important either that the new state is completely down (the caller may not
* know all the variables of a server's state).
*
* The server's lock must be held. The lbprm's lock will be used.
*/
static void fas_set_server_status_down(struct server *srv)
{
struct proxy *p = srv->proxy;
if (!srv_lb_status_changed(srv))
return;
if (srv_willbe_usable(srv))
goto out_update_state;
HA_SPIN_LOCK(LBPRM_LOCK, &p->lbprm.lock);
if (!srv_currently_usable(srv))
/* server was already down */
goto out_update_backend;
if (srv->flags & SRV_F_BACKUP) {
p->lbprm.tot_wbck -= srv->cur_eweight;
p->srv_bck--;
if (srv == p->lbprm.fbck) {
/* we lost the first backup server in a single-backup
* configuration, we must search another one.
*/
struct server *srv2 = p->lbprm.fbck;
do {
srv2 = srv2->next;
} while (srv2 &&
!((srv2->flags & SRV_F_BACKUP) &&
srv_willbe_usable(srv2)));
p->lbprm.fbck = srv2;
}
} else {
p->lbprm.tot_wact -= srv->cur_eweight;
p->srv_act--;
}
fas_dequeue_srv(srv);
fas_remove_from_tree(srv);
out_update_backend:
/* check/update tot_used, tot_weight */
update_backend_weight(p);
HA_SPIN_UNLOCK(LBPRM_LOCK, &p->lbprm.lock);
out_update_state:
srv_lb_commit_status(srv);
}
/* This function updates the server trees according to server <srv>'s new
* state. It should be called when server <srv>'s status changes to up.
* It is not important whether the server was already down or not. It is not
* important either that the new state is completely UP (the caller may not
* know all the variables of a server's state). This function will not change
* the weight of a server which was already up.
*
* The server's lock must be held. The lbprm's lock will be used.
*/
static void fas_set_server_status_up(struct server *srv)
{
struct proxy *p = srv->proxy;
if (!srv_lb_status_changed(srv))
return;
if (!srv_willbe_usable(srv))
goto out_update_state;
HA_SPIN_LOCK(LBPRM_LOCK, &p->lbprm.lock);
if (srv_currently_usable(srv))
/* server was already up */
goto out_update_backend;
if (srv->flags & SRV_F_BACKUP) {
srv->lb_tree = &p->lbprm.fas.bck;
p->lbprm.tot_wbck += srv->next_eweight;
p->srv_bck++;
if (!(p->options & PR_O_USE_ALL_BK)) {
if (!p->lbprm.fbck) {
/* there was no backup server anymore */
p->lbprm.fbck = srv;
} else {
/* we may have restored a backup server prior to fbck,
* in which case it should replace it.
*/
struct server *srv2 = srv;
do {
srv2 = srv2->next;
} while (srv2 && (srv2 != p->lbprm.fbck));
if (srv2)
p->lbprm.fbck = srv;
}
}
} else {
srv->lb_tree = &p->lbprm.fas.act;
p->lbprm.tot_wact += srv->next_eweight;
p->srv_act++;
}
/* note that eweight cannot be 0 here */
fas_queue_srv(srv);
out_update_backend:
/* check/update tot_used, tot_weight */
update_backend_weight(p);
HA_SPIN_UNLOCK(LBPRM_LOCK, &p->lbprm.lock);
out_update_state:
srv_lb_commit_status(srv);
}
/* This function must be called after an update to server <srv>'s effective
* weight. It may be called after a state change too.
*
* The server's lock must be held. The lbprm's lock will be used.
*/
static void fas_update_server_weight(struct server *srv)
{
int old_state, new_state;
struct proxy *p = srv->proxy;
if (!srv_lb_status_changed(srv))
return;
/* If changing the server's weight changes its state, we simply apply
* the procedures we already have for status change. If the state
* remains down, the server is not in any tree, so it's as easy as
* updating its values. If the state remains up with different weights,
* there are some computations to perform to find a new place and
* possibly a new tree for this server.
*/
old_state = srv_currently_usable(srv);
new_state = srv_willbe_usable(srv);
if (!old_state && !new_state) {
srv_lb_commit_status(srv);
return;
}
else if (!old_state && new_state) {
fas_set_server_status_up(srv);
return;
}
else if (old_state && !new_state) {
fas_set_server_status_down(srv);
return;
}
HA_SPIN_LOCK(LBPRM_LOCK, &p->lbprm.lock);
if (srv->lb_tree)
fas_dequeue_srv(srv);
if (srv->flags & SRV_F_BACKUP) {
p->lbprm.tot_wbck += srv->next_eweight - srv->cur_eweight;
srv->lb_tree = &p->lbprm.fas.bck;
} else {
p->lbprm.tot_wact += srv->next_eweight - srv->cur_eweight;
srv->lb_tree = &p->lbprm.fas.act;
}
fas_queue_srv(srv);
update_backend_weight(p);
HA_SPIN_UNLOCK(LBPRM_LOCK, &p->lbprm.lock);
srv_lb_commit_status(srv);
}
/* This function is responsible for building the trees in case of fast
* weighted least-conns. It also sets p->lbprm.wdiv to the eweight to
* uweight ratio. Both active and backup groups are initialized.
*/
void fas_init_server_tree(struct proxy *p)
{
struct server *srv;
struct eb_root init_head = EB_ROOT;
p->lbprm.set_server_status_up = fas_set_server_status_up;
p->lbprm.set_server_status_down = fas_set_server_status_down;
p->lbprm.update_server_eweight = fas_update_server_weight;
p->lbprm.server_take_conn = fas_srv_reposition;
p->lbprm.server_drop_conn = fas_srv_reposition;
p->lbprm.wdiv = BE_WEIGHT_SCALE;
for (srv = p->srv; srv; srv = srv->next) {
srv->next_eweight = (srv->uweight * p->lbprm.wdiv + p->lbprm.wmult - 1) / p->lbprm.wmult;
srv_lb_commit_status(srv);
}
recount_servers(p);
update_backend_weight(p);
p->lbprm.fas.act = init_head;
p->lbprm.fas.bck = init_head;
/* queue active and backup servers in two distinct groups */
for (srv = p->srv; srv; srv = srv->next) {
if (!srv_currently_usable(srv))
continue;
srv->lb_tree = (srv->flags & SRV_F_BACKUP) ? &p->lbprm.fas.bck : &p->lbprm.fas.act;
fas_queue_srv(srv);
}
}
/* Return next server from the FS tree in backend <p>. If the tree is empty,
* return NULL. Saturated servers are skipped.
*
* The server's lock must be held. The lbprm's lock will be used.
*/
struct server *fas_get_next_server(struct proxy *p, struct server *srvtoavoid)
{
struct server *srv, *avoided;
struct eb32_node *node;
srv = avoided = NULL;
HA_SPIN_LOCK(LBPRM_LOCK, &p->lbprm.lock);
if (p->srv_act)
node = eb32_first(&p->lbprm.fas.act);
else if (p->lbprm.fbck) {
srv = p->lbprm.fbck;
goto out;
}
else if (p->srv_bck)
node = eb32_first(&p->lbprm.fas.bck);
else {
srv = NULL;
goto out;
}
while (node) {
/* OK, we have a server. However, it may be saturated, in which
* case we don't want to reconsider it for now, so we'll simply
* skip it. Same if it's the server we try to avoid, in which
* case we simply remember it for later use if needed.
*/
struct server *s;
s = eb32_entry(node, struct server, lb_node);
if (!s->maxconn || (!s->nbpend && s->served < srv_dynamic_maxconn(s))) {
if (s != srvtoavoid) {
srv = s;
break;
}
avoided = s;
}
node = eb32_next(node);
}
if (!srv)
srv = avoided;
out:
HA_SPIN_UNLOCK(LBPRM_LOCK, &p->lbprm.lock);
return srv;
}
/*
* Local variables:
* c-indent-level: 8
* c-basic-offset: 8
* End:
*/