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-rw-r--r--src/lb_fwlc.c375
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diff --git a/src/lb_fwlc.c b/src/lb_fwlc.c
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+/*
+ * Fast Weighted Least Connection 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/api.h>
+#include <haproxy/backend.h>
+#include <haproxy/queue.h>
+#include <haproxy/server-t.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 fwlc_remove_from_tree(struct server *s)
+{
+ s->lb_tree = NULL;
+}
+
+/* simply removes a server from a tree.
+ *
+ * The lbprm's lock must be held.
+ */
+static inline void fwlc_dequeue_srv(struct server *s)
+{
+ eb32_delete(&s->lb_node);
+}
+
+/* Queue a server in its associated tree, assuming the <eweight> is >0.
+ * Servers are sorted by (#conns+1)/weight. To ensure maximum accuracy,
+ * we use (#conns+1)*SRV_EWGHT_MAX/eweight as the sorting key. The reason
+ * for using #conns+1 is to sort by weights in case the server is picked
+ * and not before it is picked. This provides a better load accuracy for
+ * low connection counts when weights differ and makes sure the round-robin
+ * applies between servers of highest weight first. However servers with no
+ * connection are always picked first so that under low loads, it's not
+ * always the single server with the highest weight that gets picked.
+ *
+ * NOTE: Depending on the calling context, we use s->next_eweight or
+ * s->cur_eweight. The next value is used when the server state is updated
+ * (because the weight changed for instance). During this step, the server
+ * state is not yet committed. The current value is used to reposition the
+ * server in the tree. This happens when the server is used.
+ *
+ * The lbprm's lock must be held.
+ */
+static inline void fwlc_queue_srv(struct server *s, unsigned int eweight)
+{
+ unsigned int inflight = _HA_ATOMIC_LOAD(&s->served) + _HA_ATOMIC_LOAD(&s->queue.length);
+
+ s->lb_node.key = inflight ? (inflight + 1) * SRV_EWGHT_MAX / eweight : 0;
+ eb32_insert(s->lb_tree, &s->lb_node);
+}
+
+/* Re-position the server in the FWLC 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 lbprm's lock will be used.
+ */
+static void fwlc_srv_reposition(struct server *s)
+{
+ unsigned int inflight = _HA_ATOMIC_LOAD(&s->served) + _HA_ATOMIC_LOAD(&s->queue.length);
+ unsigned int eweight = _HA_ATOMIC_LOAD(&s->cur_eweight);
+ unsigned int new_key = inflight ? (inflight + 1) * SRV_EWGHT_MAX / (eweight ? eweight : 1) : 0;
+
+ /* some calls will be made for no change (e.g connect_server() after
+ * assign_server(). Let's check that first.
+ */
+ if (s->lb_node.node.leaf_p && eweight && s->lb_node.key == new_key)
+ return;
+
+ HA_RWLOCK_WRLOCK(LBPRM_LOCK, &s->proxy->lbprm.lock);
+ if (s->lb_tree) {
+ /* we might have been waiting for a while on the lock above
+ * so it's worth testing again because other threads are very
+ * likely to have released a connection or taken one leading
+ * to our target value (50% of the case in measurements).
+ */
+ inflight = _HA_ATOMIC_LOAD(&s->served) + _HA_ATOMIC_LOAD(&s->queue.length);
+ eweight = _HA_ATOMIC_LOAD(&s->cur_eweight);
+ new_key = inflight ? (inflight + 1) * SRV_EWGHT_MAX / (eweight ? eweight : 1) : 0;
+ if (!s->lb_node.node.leaf_p || s->lb_node.key != new_key) {
+ eb32_delete(&s->lb_node);
+ s->lb_node.key = new_key;
+ eb32_insert(s->lb_tree, &s->lb_node);
+ }
+ }
+ HA_RWLOCK_WRUNLOCK(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 fwlc_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_RWLOCK_WRLOCK(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--;
+ }
+
+ fwlc_dequeue_srv(srv);
+ fwlc_remove_from_tree(srv);
+
+out_update_backend:
+ /* check/update tot_used, tot_weight */
+ update_backend_weight(p);
+ HA_RWLOCK_WRUNLOCK(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 fwlc_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_RWLOCK_WRLOCK(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.fwlc.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.fwlc.act;
+ p->lbprm.tot_wact += srv->next_eweight;
+ p->srv_act++;
+ }
+
+ /* note that eweight cannot be 0 here */
+ fwlc_queue_srv(srv, srv->next_eweight);
+
+ out_update_backend:
+ /* check/update tot_used, tot_weight */
+ update_backend_weight(p);
+ HA_RWLOCK_WRUNLOCK(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 fwlc_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) {
+ fwlc_set_server_status_up(srv);
+ return;
+ }
+ else if (old_state && !new_state) {
+ fwlc_set_server_status_down(srv);
+ return;
+ }
+
+ HA_RWLOCK_WRLOCK(LBPRM_LOCK, &p->lbprm.lock);
+
+ if (srv->lb_tree)
+ fwlc_dequeue_srv(srv);
+
+ if (srv->flags & SRV_F_BACKUP) {
+ p->lbprm.tot_wbck += srv->next_eweight - srv->cur_eweight;
+ srv->lb_tree = &p->lbprm.fwlc.bck;
+ } else {
+ p->lbprm.tot_wact += srv->next_eweight - srv->cur_eweight;
+ srv->lb_tree = &p->lbprm.fwlc.act;
+ }
+
+ fwlc_queue_srv(srv, srv->next_eweight);
+
+ update_backend_weight(p);
+ HA_RWLOCK_WRUNLOCK(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 fwlc_init_server_tree(struct proxy *p)
+{
+ struct server *srv;
+ struct eb_root init_head = EB_ROOT;
+
+ p->lbprm.set_server_status_up = fwlc_set_server_status_up;
+ p->lbprm.set_server_status_down = fwlc_set_server_status_down;
+ p->lbprm.update_server_eweight = fwlc_update_server_weight;
+ p->lbprm.server_take_conn = fwlc_srv_reposition;
+ p->lbprm.server_drop_conn = fwlc_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.fwlc.act = init_head;
+ p->lbprm.fwlc.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.fwlc.bck : &p->lbprm.fwlc.act;
+ fwlc_queue_srv(srv, srv->next_eweight);
+ }
+}
+
+/* Return next server from the FWLC tree in backend <p>. If the tree is empty,
+ * return NULL. Saturated servers are skipped.
+ *
+ * The lbprm's lock will be used in R/O mode. The server's lock is not used.
+ */
+struct server *fwlc_get_next_server(struct proxy *p, struct server *srvtoavoid)
+{
+ struct server *srv, *avoided;
+ struct eb32_node *node;
+
+ srv = avoided = NULL;
+
+ HA_RWLOCK_RDLOCK(LBPRM_LOCK, &p->lbprm.lock);
+ if (p->srv_act)
+ node = eb32_first(&p->lbprm.fwlc.act);
+ else if (p->lbprm.fbck) {
+ srv = p->lbprm.fbck;
+ goto out;
+ }
+ else if (p->srv_bck)
+ node = eb32_first(&p->lbprm.fwlc.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->served + s->queue.length < srv_dynamic_maxconn(s) + s->maxqueue) {
+ if (s != srvtoavoid) {
+ srv = s;
+ break;
+ }
+ avoided = s;
+ }
+ node = eb32_next(node);
+ }
+
+ if (!srv)
+ srv = avoided;
+ out:
+ HA_RWLOCK_RDUNLOCK(LBPRM_LOCK, &p->lbprm.lock);
+ return srv;
+}
+
+
+/*
+ * Local variables:
+ * c-indent-level: 8
+ * c-basic-offset: 8
+ * End:
+ */