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/*
* Fast Weighted Round Robin load balancing algorithm.
*
* Copyright 2000-2009 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 <import/eb32tree.h>
#include <haproxy/backend.h>
#include <haproxy/api.h>
#include <haproxy/queue.h>
#include <haproxy/server-t.h>
static inline void fwrr_remove_from_tree(struct server *s);
static inline void fwrr_queue_by_weight(struct eb_root *root, struct server *s);
static inline void fwrr_dequeue_srv(struct server *s);
static void fwrr_get_srv(struct server *s);
static void fwrr_queue_srv(struct server *s);
/* 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 fwrr_set_server_status_down(struct server *srv)
{
struct proxy *p = srv->proxy;
struct fwrr_group *grp;
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;
grp = (srv->flags & SRV_F_BACKUP) ? &p->lbprm.fwrr.bck : &p->lbprm.fwrr.act;
grp->next_weight -= srv->cur_eweight;
if (srv->flags & SRV_F_BACKUP) {
p->lbprm.tot_wbck = p->lbprm.fwrr.bck.next_weight;
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 = p->lbprm.fwrr.act.next_weight;
p->srv_act--;
}
fwrr_dequeue_srv(srv);
fwrr_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 fwrr_set_server_status_up(struct server *srv)
{
struct proxy *p = srv->proxy;
struct fwrr_group *grp;
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;
grp = (srv->flags & SRV_F_BACKUP) ? &p->lbprm.fwrr.bck : &p->lbprm.fwrr.act;
grp->next_weight += srv->next_eweight;
if (srv->flags & SRV_F_BACKUP) {
p->lbprm.tot_wbck = p->lbprm.fwrr.bck.next_weight;
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 {
p->lbprm.tot_wact = p->lbprm.fwrr.act.next_weight;
p->srv_act++;
}
/* note that eweight cannot be 0 here */
fwrr_get_srv(srv);
srv->npos = grp->curr_pos + (grp->next_weight + grp->curr_weight - grp->curr_pos) / srv->next_eweight;
fwrr_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 fwrr_update_server_weight(struct server *srv)
{
int old_state, new_state;
struct proxy *p = srv->proxy;
struct fwrr_group *grp;
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) {
fwrr_set_server_status_up(srv);
return;
}
else if (old_state && !new_state) {
fwrr_set_server_status_down(srv);
return;
}
HA_SPIN_LOCK(LBPRM_LOCK, &p->lbprm.lock);
grp = (srv->flags & SRV_F_BACKUP) ? &p->lbprm.fwrr.bck : &p->lbprm.fwrr.act;
grp->next_weight = grp->next_weight - srv->cur_eweight + srv->next_eweight;
p->lbprm.tot_wact = p->lbprm.fwrr.act.next_weight;
p->lbprm.tot_wbck = p->lbprm.fwrr.bck.next_weight;
if (srv->lb_tree == grp->init) {
fwrr_dequeue_srv(srv);
fwrr_queue_by_weight(grp->init, srv);
}
else if (!srv->lb_tree) {
/* FIXME: server was down. This is not possible right now but
* may be needed soon for slowstart or graceful shutdown.
*/
fwrr_dequeue_srv(srv);
fwrr_get_srv(srv);
srv->npos = grp->curr_pos + (grp->next_weight + grp->curr_weight - grp->curr_pos) / srv->next_eweight;
fwrr_queue_srv(srv);
} else {
/* The server is either active or in the next queue. If it's
* still in the active queue and it has not consumed all of its
* places, let's adjust its next position.
*/
fwrr_get_srv(srv);
if (srv->next_eweight > 0) {
int prev_next = srv->npos;
int step = grp->next_weight / srv->next_eweight;
srv->npos = srv->lpos + step;
srv->rweight = 0;
if (srv->npos > prev_next)
srv->npos = prev_next;
if (srv->npos < grp->curr_pos + 2)
srv->npos = grp->curr_pos + step;
} else {
/* push it into the next tree */
srv->npos = grp->curr_pos + grp->curr_weight;
}
fwrr_dequeue_srv(srv);
fwrr_queue_srv(srv);
}
update_backend_weight(p);
HA_SPIN_UNLOCK(LBPRM_LOCK, &p->lbprm.lock);
srv_lb_commit_status(srv);
}
/* 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 lbprm's lock must be held. The server's lock is not used.
*/
static inline void fwrr_remove_from_tree(struct server *s)
{
s->lb_tree = NULL;
}
/* Queue a server in the weight tree <root>, assuming the weight is >0.
* We want to sort them by inverted weights, because we need to place
* heavy servers first in order to get a smooth distribution.
*
* The lbprm's lock must be held. The server's lock is not used.
*/
static inline void fwrr_queue_by_weight(struct eb_root *root, struct server *s)
{
s->lb_node.key = SRV_EWGHT_MAX - s->next_eweight;
eb32_insert(root, &s->lb_node);
s->lb_tree = root;
}
/* This function is responsible for building the weight trees in case of fast
* weighted round-robin. It also sets p->lbprm.wdiv to the eweight to uweight
* ratio. Both active and backup groups are initialized.
*/
void fwrr_init_server_groups(struct proxy *p)
{
struct server *srv;
struct eb_root init_head = EB_ROOT;
p->lbprm.set_server_status_up = fwrr_set_server_status_up;
p->lbprm.set_server_status_down = fwrr_set_server_status_down;
p->lbprm.update_server_eweight = fwrr_update_server_weight;
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);
/* prepare the active servers group */
p->lbprm.fwrr.act.curr_pos = p->lbprm.fwrr.act.curr_weight =
p->lbprm.fwrr.act.next_weight = p->lbprm.tot_wact;
p->lbprm.fwrr.act.curr = p->lbprm.fwrr.act.t0 =
p->lbprm.fwrr.act.t1 = init_head;
p->lbprm.fwrr.act.init = &p->lbprm.fwrr.act.t0;
p->lbprm.fwrr.act.next = &p->lbprm.fwrr.act.t1;
/* prepare the backup servers group */
p->lbprm.fwrr.bck.curr_pos = p->lbprm.fwrr.bck.curr_weight =
p->lbprm.fwrr.bck.next_weight = p->lbprm.tot_wbck;
p->lbprm.fwrr.bck.curr = p->lbprm.fwrr.bck.t0 =
p->lbprm.fwrr.bck.t1 = init_head;
p->lbprm.fwrr.bck.init = &p->lbprm.fwrr.bck.t0;
p->lbprm.fwrr.bck.next = &p->lbprm.fwrr.bck.t1;
/* queue active and backup servers in two distinct groups */
for (srv = p->srv; srv; srv = srv->next) {
if (!srv_currently_usable(srv))
continue;
fwrr_queue_by_weight((srv->flags & SRV_F_BACKUP) ?
p->lbprm.fwrr.bck.init :
p->lbprm.fwrr.act.init,
srv);
}
}
/* simply removes a server from a weight tree.
*
* The lbprm's lock must be held. The server's lock is not used.
*/
static inline void fwrr_dequeue_srv(struct server *s)
{
eb32_delete(&s->lb_node);
}
/* queues a server into the appropriate group and tree depending on its
* backup status, and ->npos. If the server is disabled, simply assign
* it to the NULL tree.
*
* The lbprm's lock must be held. The server's lock is not used.
*/
static void fwrr_queue_srv(struct server *s)
{
struct proxy *p = s->proxy;
struct fwrr_group *grp;
grp = (s->flags & SRV_F_BACKUP) ? &p->lbprm.fwrr.bck : &p->lbprm.fwrr.act;
/* Delay everything which does not fit into the window and everything
* which does not fit into the theorical new window.
*/
if (!srv_willbe_usable(s)) {
fwrr_remove_from_tree(s);
}
else if (s->next_eweight <= 0 ||
s->npos >= 2 * grp->curr_weight ||
s->npos >= grp->curr_weight + grp->next_weight) {
/* put into next tree, and readjust npos in case we could
* finally take this back to current. */
s->npos -= grp->curr_weight;
fwrr_queue_by_weight(grp->next, s);
}
else {
/* The sorting key is stored in units of s->npos * user_weight
* in order to avoid overflows. As stated in backend.h, the
* lower the scale, the rougher the weights modulation, and the
* higher the scale, the lower the number of servers without
* overflow. With this formula, the result is always positive,
* so we can use eb32_insert().
*/
s->lb_node.key = SRV_UWGHT_RANGE * s->npos +
(unsigned)(SRV_EWGHT_MAX + s->rweight - s->next_eweight) / BE_WEIGHT_SCALE;
eb32_insert(&grp->curr, &s->lb_node);
s->lb_tree = &grp->curr;
}
}
/* prepares a server when extracting it from the "init" tree.
*
* The lbprm's lock must be held. The server's lock is not used.
*/
static inline void fwrr_get_srv_init(struct server *s)
{
s->npos = s->rweight = 0;
}
/* prepares a server when extracting it from the "next" tree.
*
* The lbprm's lock must be held. The server's lock is not used.
*/
static inline void fwrr_get_srv_next(struct server *s)
{
struct fwrr_group *grp = (s->flags & SRV_F_BACKUP) ?
&s->proxy->lbprm.fwrr.bck :
&s->proxy->lbprm.fwrr.act;
s->npos += grp->curr_weight;
}
/* prepares a server when it was marked down.
*
* The lbprm's lock must be held. The server's lock is not used.
*/
static inline void fwrr_get_srv_down(struct server *s)
{
struct fwrr_group *grp = (s->flags & SRV_F_BACKUP) ?
&s->proxy->lbprm.fwrr.bck :
&s->proxy->lbprm.fwrr.act;
s->npos = grp->curr_pos;
}
/* prepares a server when extracting it from its tree.
*
* The lbprm's lock must be held. The server's lock is not used.
*/
static void fwrr_get_srv(struct server *s)
{
struct proxy *p = s->proxy;
struct fwrr_group *grp = (s->flags & SRV_F_BACKUP) ?
&p->lbprm.fwrr.bck :
&p->lbprm.fwrr.act;
if (s->lb_tree == grp->init) {
fwrr_get_srv_init(s);
}
else if (s->lb_tree == grp->next) {
fwrr_get_srv_next(s);
}
else if (s->lb_tree == NULL) {
fwrr_get_srv_down(s);
}
}
/* switches trees "init" and "next" for FWRR group <grp>. "init" should be empty
* when this happens, and "next" filled with servers sorted by weights.
*
* The lbprm's lock must be held. The server's lock is not used.
*/
static inline void fwrr_switch_trees(struct fwrr_group *grp)
{
struct eb_root *swap;
swap = grp->init;
grp->init = grp->next;
grp->next = swap;
grp->curr_weight = grp->next_weight;
grp->curr_pos = grp->curr_weight;
}
/* return next server from the current tree in FWRR group <grp>, or a server
* from the "init" tree if appropriate. If both trees are empty, return NULL.
*
* The lbprm's lock must be held. The server's lock is not used.
*/
static struct server *fwrr_get_server_from_group(struct fwrr_group *grp)
{
struct eb32_node *node1;
struct eb32_node *node2;
struct server *s1 = NULL;
struct server *s2 = NULL;
node1 = eb32_first(&grp->curr);
if (node1) {
s1 = eb32_entry(node1, struct server, lb_node);
if (s1->cur_eweight && s1->npos <= grp->curr_pos)
return s1;
}
/* Either we have no server left, or we have a hole. We'll look in the
* init tree or a better proposal. At this point, if <s1> is non-null,
* it is guaranteed to remain available as the tree is locked.
*/
node2 = eb32_first(grp->init);
if (node2) {
s2 = eb32_entry(node2, struct server, lb_node);
if (s2->cur_eweight) {
fwrr_get_srv_init(s2);
return s2;
}
}
return s1;
}
/* Computes next position of server <s> in the group. Nothing is done if <s>
* has a zero weight.
*
* The lbprm's lock must be held to protect lpos/npos/rweight.
*/
static inline void fwrr_update_position(struct fwrr_group *grp, struct server *s)
{
unsigned int eweight = *(volatile unsigned int *)&s->cur_eweight;
if (!eweight)
return;
if (!s->npos) {
/* first time ever for this server */
s->npos = grp->curr_pos;
}
s->lpos = s->npos;
s->npos += grp->next_weight / eweight;
s->rweight += grp->next_weight % eweight;
if (s->rweight >= eweight) {
s->rweight -= eweight;
s->npos++;
}
}
/* Return next server from the current tree in backend <p>, or a server from
* the init tree if appropriate. If both trees are empty, return NULL.
* Saturated servers are skipped and requeued.
*
* The lbprm's lock will be used. The server's lock is not used.
*/
struct server *fwrr_get_next_server(struct proxy *p, struct server *srvtoavoid)
{
struct server *srv, *full, *avoided;
struct fwrr_group *grp;
int switched;
HA_SPIN_LOCK(LBPRM_LOCK, &p->lbprm.lock);
if (p->srv_act)
grp = &p->lbprm.fwrr.act;
else if (p->lbprm.fbck) {
srv = p->lbprm.fbck;
goto out;
}
else if (p->srv_bck)
grp = &p->lbprm.fwrr.bck;
else {
srv = NULL;
goto out;
}
switched = 0;
avoided = NULL;
full = NULL; /* NULL-terminated list of saturated servers */
while (1) {
/* if we see an empty group, let's first try to collect weights
* which might have recently changed.
*/
if (!grp->curr_weight)
grp->curr_pos = grp->curr_weight = grp->next_weight;
/* get first server from the "current" tree. When the end of
* the tree is reached, we may have to switch, but only once.
*/
while (1) {
srv = fwrr_get_server_from_group(grp);
if (srv)
break;
if (switched) {
if (avoided) {
srv = avoided;
goto take_this_one;
}
goto requeue_servers;
}
switched = 1;
fwrr_switch_trees(grp);
}
/* OK, we have a server. However, it may be saturated, in which
* case we don't want to reconsider it for now. We'll update
* its position and dequeue it anyway, so that we can move it
* to a better place afterwards.
*/
fwrr_update_position(grp, srv);
fwrr_dequeue_srv(srv);
grp->curr_pos++;
if (!srv->maxconn || (!srv->nbpend && srv->served < srv_dynamic_maxconn(srv))) {
/* make sure it is not the server we are trying to exclude... */
if (srv != srvtoavoid || avoided)
break;
avoided = srv; /* ...but remember that is was selected yet avoided */
}
/* the server is saturated or avoided, let's chain it for later reinsertion.
*/
srv->next_full = full;
full = srv;
}
take_this_one:
/* OK, we got the best server, let's update it */
fwrr_queue_srv(srv);
requeue_servers:
/* Requeue all extracted servers. If full==srv then it was
* avoided (unsuccessfully) and chained, omit it now. The
* only way to get there is by having <avoided>==NULL or
* <avoided>==<srv>.
*/
if (unlikely(full != NULL)) {
if (switched) {
/* the tree has switched, requeue all extracted servers
* into "init", because their place was lost, and only
* their weight matters.
*/
do {
if (likely(full != srv))
fwrr_queue_by_weight(grp->init, full);
full = full->next_full;
} while (full);
} else {
/* requeue all extracted servers just as if they were consumed
* so that they regain their expected place.
*/
do {
if (likely(full != srv))
fwrr_queue_srv(full);
full = full->next_full;
} while (full);
}
}
out:
HA_SPIN_UNLOCK(LBPRM_LOCK, &p->lbprm.lock);
return srv;
}
/*
* Local variables:
* c-indent-level: 8
* c-basic-offset: 8
* End:
*/