From 98c8910be748fa3a3f3ff6bff77b89177f5fd350 Mon Sep 17 00:00:00 2001
From: Willy Tarreau <w@1wt.eu>
Date: Fri, 18 Jun 2021 10:51:58 +0200
Subject: [PATCH] MINOR: queue: use atomic-ops to update the queue's index (v2)

Doing so allows to retrieve and update the pendconn's queue index outside
of the queue's lock and to save one more percent CPU on a highly-contented
backend.
---
 src/queue.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/src/queue.c b/src/queue.c
index d9cae318b..1aa3fb9ac 100644
--- a/src/queue.c
+++ b/src/queue.c
@@ -133,7 +133,7 @@ unsigned int srv_dynamic_maxconn(const struct server *s)
  */
 static void __pendconn_unlink_srv(struct pendconn *p)
 {
-	p->strm->logs.srv_queue_pos += p->srv->queue.idx - p->queue_idx;
+	p->strm->logs.srv_queue_pos += _HA_ATOMIC_LOAD(&p->srv->queue.idx) - p->queue_idx;
 	eb32_delete(&p->node);
 }
 
@@ -146,7 +146,7 @@ static void __pendconn_unlink_srv(struct pendconn *p)
  */
 static void __pendconn_unlink_prx(struct pendconn *p)
 {
-	p->strm->logs.prx_queue_pos += p->px->queue.idx - p->queue_idx;
+	p->strm->logs.prx_queue_pos += _HA_ATOMIC_LOAD(&p->px->queue.idx) - p->queue_idx;
 	eb32_delete(&p->node);
 }
 
@@ -305,13 +305,13 @@ static int pendconn_process_next_strm(struct server *srv, struct proxy *px, int
 	/* Let's switch from the server pendconn to the proxy pendconn */
 	__pendconn_unlink_prx(pp);
 	_HA_ATOMIC_DEC(&px->queue.length);
-	px->queue.idx++;
+	_HA_ATOMIC_INC(&px->queue.idx);
 	p = pp;
 	goto unlinked;
  use_p:
 	__pendconn_unlink_srv(p);
 	_HA_ATOMIC_DEC(&srv->queue.length);
-	srv->queue.idx++;
+	_HA_ATOMIC_INC(&srv->queue.idx);
  unlinked:
 	p->strm_flags |= SF_ASSIGNED;
 	p->target = srv;
@@ -419,6 +419,7 @@ struct pendconn *pendconn_add(struct stream *strm)
 		max_ptr = &px->be_counters.nbpend_max;
 	}
 
+	p->queue_idx  = _HA_ATOMIC_LOAD(&q->idx) - 1; // for logging only
 	new_max = _HA_ATOMIC_ADD_FETCH(&q->length, 1);
 	old_max = _HA_ATOMIC_LOAD(max_ptr);
 	while (new_max > old_max) {
@@ -428,7 +429,6 @@ struct pendconn *pendconn_add(struct stream *strm)
 	__ha_barrier_atomic_store();
 
 	HA_SPIN_LOCK(QUEUE_LOCK, &q->lock);
-	p->queue_idx = q->idx - 1; // for increment
 	eb32_insert(&q->head, &p->node);
 	HA_SPIN_UNLOCK(QUEUE_LOCK, &q->lock);