From: Willy Tarreau <w@1wt.eu>
Date: Fri, 13 Nov 2026 10:06:31 +0000 (+0100)
Subject: OPTIM: lb-chash: don't look for more servers when there is only one
X-Git-Url: https://git.kaiwu.me/ngx_http_access_module.html?a=commitdiff_plain;h=d9550ce4f300dc4b0a2b076da65a2e1978fbdf62;p=haproxy.git

OPTIM: lb-chash: don't look for more servers when there is only one

The chash_get_server_hash() function never makes a special case for a
single server. Worse, when asked to avoid a specific one and it is the
only one, or when the chosen server is not eligible, the function will
run over all its positions at the end. Thus having a single server in
a config with a weight 256 and asking to avoid it burns a lot of CPU.

Let's just test for this case after picking the first server. If the
total servers count is 1, we can just leave.
---

diff --git a/src/lb_chash.c b/src/lb_chash.c
index 12a933a21..cc63a9ae7 100644
--- a/src/lb_chash.c
+++ b/src/lb_chash.c
@@ -419,18 +419,19 @@ struct server *chash_get_server_hash(struct proxy *p, unsigned int hash, const s
 	struct server *nsrv, *psrv;
 	struct eb_root *root;
 	unsigned int dn, dp;
+	int tot = 0;
 	int loop;
 	int hashafnty;
 
 	HA_RWLOCK_RDLOCK(LBPRM_LOCK, &p->lbprm.lock);
 
-	if (p->srv_act)
+	if ((tot = p->srv_act))
 		root = &p->lbprm.chash.act;
 	else if (p->lbprm.fbck) {
 		nsrv = p->lbprm.fbck;
 		goto out;
 	}
-	else if (p->srv_bck)
+	else if ((tot = p->srv_bck))
 		root = &p->lbprm.chash.bck;
 	else {
 		nsrv = NULL;
@@ -446,11 +447,16 @@ struct server *chash_get_server_hash(struct proxy *p, unsigned int hash, const s
 		goto out;
 	}
 
+	nsrv = eb32_entry(next, struct tree_occ, node)->server;
+
+	/* if there's only one server, no need to go further */
+	if (tot == 1)
+		goto out;
+
 	prev = eb32_prev(next);
 	if (!prev)
 		prev = eb32_last(root);
 
-	nsrv = eb32_entry(next, struct tree_occ, node)->server;
 	psrv = eb32_entry(prev, struct tree_occ, node)->server;
 
 	/* OK we're located between two servers, let's