1 files changed, 348 insertions, 0 deletions
diff --git a/src/lb_fas.c b/src/lb_fas.c
new file mode 100644
index 0000000..d90388b
--- /dev/null
+++ b/src/lb_fas.c
@@ -0,0 +1,348 @@
+/*
+ * 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 <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 fas_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 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 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 lbprm's lock will be used.
+ */
+static void fas_srv_reposition(struct server *s)
+{
+	HA_RWLOCK_WRLOCK(LBPRM_LOCK, &s->proxy->lbprm.lock);
+	if (s->lb_tree) {
+		fas_dequeue_srv(s);
+		fas_queue_srv(s);
+	}
+	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 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_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--;
+	}
+
+	fas_dequeue_srv(srv);
+	fas_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 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_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.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_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 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_RWLOCK_WRLOCK(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_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 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 lbprm's lock will be used. The server's lock is not 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_RWLOCK_RDLOCK(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->queue.length && s->served < srv_dynamic_maxconn(s))) {
+			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:
+ */