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MEDIUM: queue: use a dedicated lock for the queues

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Till now whenever a server or proxy's queue was touched, this server
or proxy's lock was taken. Not only this requires distinct code paths,
but it also causes unnecessary contention with other uses of these locks.

This patch adds a lock inside the "queue" structure that will be used
the same way by the server and the proxy queuing code. The server used
to use a spinlock and the proxy an rwlock, though the queue only used
it for locked writes. This new version uses a spinlock since we don't
need the read lock part here. Tests have not shown any benefit nor cost
in using this one versus the rwlock so we could change later if needed.

The lower contention on the locks increases the performance from 491k
to 507k req/s on 16 threads with 20 servers and leastconn. The gain
with roundrobin even increases by 6%.

The performance profile changes from this:
  13.03%  haproxy             [.] fwlc_srv_reposition
   8.08%  haproxy             [.] fwlc_get_next_server
   3.62%  haproxy             [.] process_srv_queue
   1.78%  haproxy             [.] pendconn_dequeue
   1.74%  haproxy             [.] pendconn_add

to this:
  11.95%  haproxy             [.] fwlc_srv_reposition
   7.57%  haproxy             [.] fwlc_get_next_server
   3.51%  haproxy             [.] process_srv_queue
   1.74%  haproxy             [.] pendconn_dequeue
   1.70%  haproxy             [.] pendconn_add

At this point the differences are mostly measurement noise.

This is tagged medium because the lock is changed, but no other part of
the code touches the queues, with nor without locking, so this should
remain invisible.
This commit is contained in:
Willy Tarreau 2021-06-18 09:45:27 +02:00
parent a05704582c
commit fcb8bf8650
5 changed files with 26 additions and 23 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
include/haproxy/queue-t.h
View File

@ -41,6 +41,7 @@ struct pendconn {
struct queue {
struct eb_root head; /* queued pendconnds */
__decl_thread(HA_SPINLOCK_T lock); /* for manipulations in the tree */
unsigned int idx; /* current queuing index */
unsigned int length; /* number of entries */
};

2
include/haproxy/thread.h
View File

@ -399,6 +399,7 @@ enum lock_label {
LOGSRV_LOCK,
DICT_LOCK,
PROTO_LOCK,
QUEUE_LOCK,
CKCH_LOCK,
SNI_LOCK,
SSL_SERVER_LOCK,
@ -451,6 +452,7 @@ static inline const char *lock_label(enum lock_label label)
case LOGSRV_LOCK: return "LOGSRV";
case DICT_LOCK: return "DICT";
case PROTO_LOCK: return "PROTO";
case QUEUE_LOCK: return "QUEUE";
case CKCH_LOCK: return "CKCH";
case SNI_LOCK: return "SNI";
case SSL_SERVER_LOCK: return "SSL_SERVER";

1
src/proxy.c
View File

@ -1293,6 +1293,7 @@ void init_new_proxy(struct proxy *p)
memset(p, 0, sizeof(struct proxy));
p->obj_type = OBJ_TYPE_PROXY;
p->queue.head = EB_ROOT;
HA_SPIN_INIT(&p->queue.lock);
LIST_INIT(&p->acl);
LIST_INIT(&p->http_req_rules);
LIST_INIT(&p->http_res_rules);

44
src/queue.c
View File

@ -157,9 +157,9 @@ static void __pendconn_unlink_prx(struct pendconn *p)
static inline void pendconn_queue_lock(struct pendconn *p)
{
if (p->srv)
HA_SPIN_LOCK(SERVER_LOCK, &p->srv->lock);
HA_SPIN_LOCK(QUEUE_LOCK, &p->srv->queue.lock);
else
HA_RWLOCK_WRLOCK(PROXY_LOCK, &p->px->lock);
HA_SPIN_LOCK(QUEUE_LOCK, &p->px->queue.lock);
}
/* Unlocks the queue the pendconn element belongs to. This relies on both p->px
@ -169,9 +169,9 @@ static inline void pendconn_queue_lock(struct pendconn *p)
static inline void pendconn_queue_unlock(struct pendconn *p)
{
if (p->srv)
HA_SPIN_UNLOCK(SERVER_LOCK, &p->srv->lock);
HA_SPIN_UNLOCK(QUEUE_LOCK, &p->srv->queue.lock);
else
HA_RWLOCK_WRUNLOCK(PROXY_LOCK, &p->px->lock);
HA_SPIN_UNLOCK(QUEUE_LOCK, &p->px->queue.lock);
}
/* Removes the pendconn from the server/proxy queue. At this stage, the
@ -187,12 +187,12 @@ void pendconn_unlink(struct pendconn *p)
if (p->srv) {
/* queued in the server */
HA_SPIN_LOCK(SERVER_LOCK, &p->srv->lock);
HA_SPIN_LOCK(QUEUE_LOCK, &p->srv->queue.lock);
if (p->node.node.leaf_p) {
__pendconn_unlink_srv(p);
done = 1;
}
HA_SPIN_UNLOCK(SERVER_LOCK, &p->srv->lock);
HA_SPIN_UNLOCK(QUEUE_LOCK, &p->srv->queue.lock);
if (done) {
_HA_ATOMIC_DEC(&p->srv->queue.length);
_HA_ATOMIC_DEC(&p->px->totpend);
@ -200,12 +200,12 @@ void pendconn_unlink(struct pendconn *p)
}
else {
/* queued in the proxy */
HA_RWLOCK_WRLOCK(PROXY_LOCK, &p->px->lock);
HA_SPIN_LOCK(QUEUE_LOCK, &p->px->queue.lock);
if (p->node.node.leaf_p) {
__pendconn_unlink_prx(p);
done = 1;
}
HA_RWLOCK_WRUNLOCK(PROXY_LOCK, &p->px->lock);
HA_SPIN_UNLOCK(QUEUE_LOCK, &p->px->queue.lock);
if (done) {
_HA_ATOMIC_DEC(&p->px->queue.length);
_HA_ATOMIC_DEC(&p->px->totpend);
@ -344,15 +344,13 @@ void process_srv_queue(struct server *s, int server_locked)
while (s->served < maxconn) {
struct pendconn *pc;
if (!server_locked)
HA_SPIN_LOCK(SERVER_LOCK, &s->lock);
HA_RWLOCK_WRLOCK(PROXY_LOCK, &p->lock);
HA_SPIN_LOCK(QUEUE_LOCK, &s->queue.lock);
HA_SPIN_LOCK(QUEUE_LOCK, &p->queue.lock);
pc = pendconn_process_next_strm(s, p);
HA_RWLOCK_WRUNLOCK(PROXY_LOCK, &p->lock);
if (!server_locked)
HA_SPIN_UNLOCK(SERVER_LOCK, &s->lock);
HA_SPIN_UNLOCK(QUEUE_LOCK, &p->queue.lock);
HA_SPIN_UNLOCK(QUEUE_LOCK, &s->queue.lock);
if (!pc)
break;
@ -424,10 +422,10 @@ struct pendconn *pendconn_add(struct stream *strm)
}
__ha_barrier_atomic_store();
HA_SPIN_LOCK(SERVER_LOCK, &p->srv->lock);
HA_SPIN_LOCK(QUEUE_LOCK, &p->srv->queue.lock);
p->queue_idx = srv->queue.idx - 1; // for increment
eb32_insert(&srv->queue.head, &p->node);
HA_SPIN_UNLOCK(SERVER_LOCK, &p->srv->lock);
HA_SPIN_UNLOCK(QUEUE_LOCK, &p->srv->queue.lock);
}
else {
unsigned int old_max, new_max;
@ -440,10 +438,10 @@ struct pendconn *pendconn_add(struct stream *strm)
}
__ha_barrier_atomic_store();
HA_RWLOCK_WRLOCK(PROXY_LOCK, &p->px->lock);
HA_SPIN_LOCK(QUEUE_LOCK, &p->px->queue.lock);
p->queue_idx = px->queue.idx - 1; // for increment
eb32_insert(&px->queue.head, &p->node);
HA_RWLOCK_WRUNLOCK(PROXY_LOCK, &p->px->lock);
HA_SPIN_UNLOCK(QUEUE_LOCK, &p->px->queue.lock);
}
_HA_ATOMIC_INC(&px->totpend);
@ -452,7 +450,7 @@ struct pendconn *pendconn_add(struct stream *strm)
/* Redistribute pending connections when a server goes down. The number of
* connections redistributed is returned. It must be called with the server
* lock held.
* queue lock held.
*/
int pendconn_redistribute(struct server *s)
{
@ -489,8 +487,8 @@ int pendconn_redistribute(struct server *s)
/* Check for pending connections at the backend, and assign some of them to
* the server coming up. The server's weight is checked before being assigned
* connections it may not be able to handle. The total number of transferred
* connections is returned. It must be called with the server lock held, and
* will take the proxy's lock.
* connections is returned. It must be called with the server queue lock held,
* and will take the proxy's queue lock.
*/
int pendconn_grab_from_px(struct server *s)
{
@ -509,7 +507,7 @@ int pendconn_grab_from_px(struct server *s)
((s != s->proxy->lbprm.fbck) && !(s->proxy->options & PR_O_USE_ALL_BK))))
return 0;
HA_RWLOCK_WRLOCK(PROXY_LOCK, &s->proxy->lock);
HA_SPIN_LOCK(QUEUE_LOCK, &s->proxy->queue.lock);
maxconn = srv_dynamic_maxconn(s);
while ((p = pendconn_first(&s->proxy->queue.head))) {
if (s->maxconn && s->served + xferred >= maxconn)
@ -521,7 +519,7 @@ int pendconn_grab_from_px(struct server *s)
task_wakeup(p->strm->task, TASK_WOKEN_RES);
xferred++;
}
HA_RWLOCK_WRUNLOCK(PROXY_LOCK, &s->proxy->lock);
HA_SPIN_UNLOCK(QUEUE_LOCK, &s->proxy->queue.lock);
if (xferred) {
_HA_ATOMIC_SUB(&s->proxy->queue.length, xferred);
_HA_ATOMIC_SUB(&s->proxy->totpend, xferred);

1
src/server.c
View File

@ -2164,6 +2164,7 @@ struct server *new_server(struct proxy *proxy)
srv->obj_type = OBJ_TYPE_SERVER;
srv->proxy = proxy;
srv->queue.head = EB_ROOT;
HA_SPIN_INIT(&srv->queue.lock);
LIST_APPEND(&servers_list, &srv->global_list);
LIST_INIT(&srv->srv_rec_item);
LIST_INIT(&srv->ip_rec_item);