BUG/MINOR: server: start cleaning idle connections from various points

There's a minor glitch with the way idle connections start to be evicted.
The lookup always goes from thread 0 to thread N-1. This causes depletion
of connections on the first threads and abundance on the last ones. This
is visible with the takeover() stats below:

 $ socat - /tmp/sock1 <<< "show activity"|grep ^fd ; \
   sleep 10 ; \
   socat -/tmp/sock1 <<< "show activity"|grep ^fd
 fd_takeover: 300144 [ 91887 84029 66254 57974 ]
 fd_takeover: 359631 [ 111369 99699 79145 69418 ]

There are respectively 19k, 15k, 13k and 11k takeovers for only 4 threads,
indicating that the first thread needs a foreign FD twice more often than
the 4th one.

This patch changes this si that all threads are scanned in round robin
starting with the current one. The takeovers now happen in a much more
distributed way (about 4 times 9k) :

  fd_takeover: 1420081 [ 359562 359453 346586 354480 ]
  fd_takeover: 1457044 [ 368779 368429 355990 363846 ]

There is no need to backport this, as this happened along a few patches
that were merged during 2.2 development.

diff --git a/src/backend.c b/src/backend.c
index 70487870c950da5c37ab38e74e42620a153f5423..a3ec782e2ad270d061e4297a2356e58e4c261536 100644 (file)
--- a/src/backend.c
+++ b/src/backend.c
@@ -1274,10 +1274,7 @@ int connect_server(struct stream *s)
                else {
                        int i;
 
-                       for (i = 0; i < global.nbthread; i++) {
-                               if (i == tid)
-                                       continue;
-
+                       for (i = tid; (i = ((i + 1 == global.nbthread) ? 0 : i + 1)) != tid;) {
                                // just silence stupid gcc which reports an absurd
                                // out-of-bounds warning for <i> which is always
                                // exactly zero without threads, but it seems to

diff --git a/src/server.c b/src/server.c
index 1a00363e8d2dab83086364792d95494f7e32a57f..8cc5bbff68baafec357b013403a53190c248716a 100644 (file)
--- a/src/server.c
+++ b/src/server.c
@@ -5187,8 +5187,9 @@ static void srv_cleanup_connections(struct server *srv)
        int i;
        int j;
 
+       /* check all threads starting with ours */
        HA_SPIN_LOCK(OTHER_LOCK, &idle_conn_srv_lock);
-       for (i = 0; i < global.nbthread; i++) {
+       for (i = tid;;) {
                did_remove = 0;
                HA_SPIN_LOCK(OTHER_LOCK, &idle_conns[i].toremove_lock);
                for (j = 0; j < srv->curr_idle_conns; j++) {
@@ -5204,6 +5205,9 @@ static void srv_cleanup_connections(struct server *srv)
                HA_SPIN_UNLOCK(OTHER_LOCK, &idle_conns[i].toremove_lock);
                if (did_remove)
                        task_wakeup(idle_conns[i].cleanup_task, TASK_WOKEN_OTHER);
+
+               if ((i = ((i + 1 == global.nbthread) ? 0 : i + 1)) == tid)
+                       break;
        }
        HA_SPIN_UNLOCK(OTHER_LOCK, &idle_conn_srv_lock);
 }
@@ -5255,7 +5259,8 @@ struct task *srv_cleanup_idle_connections(struct task *task, void *context, unsi
                exceed_conns = to_kill = exceed_conns / 2 + (exceed_conns & 1);
                srv->max_used_conns = srv->curr_used_conns;
 
-               for (i = 0; i < global.nbthread && to_kill > 0; i++) {
+               /* check all threads starting with ours */
+               for (i = tid;;) {
                        int max_conn;
                        int j;
                        int did_remove = 0;
@@ -5278,6 +5283,9 @@ struct task *srv_cleanup_idle_connections(struct task *task, void *context, unsi
                                srv_is_empty = 0;
                        if (did_remove)
                                task_wakeup(idle_conns[i].cleanup_task, TASK_WOKEN_OTHER);
+
+                       if ((i = ((i + 1 == global.nbthread) ? 0 : i + 1)) == tid)
+                               break;
                }
 remove:
                eb32_delete(&srv->idle_node);