MINOR: quic: activate socket per conn by default

Activate QUIC connection socket to achieve the best performance. The
previous behavior can be reverted by tune.quic.socket-owner
configuration option.

This change is part of quic-conn owned socket implementation.

Contrary to its siblings patches, I suggest to not backport it to 2.7.
This should ensure that stable releases behavior is perserved. If a user
faces issues with QUIC performance on 2.7, he can nonetheless change the
default configuration.

doc/configuration.txt

@@ -3095,17 +3095,17 @@ tune.quic.socket-owner { listener | connection }
   Connections can share listener socket or each connection can allocate its
   own socket.
 
-  Default "listener" value indicates that QUIC transfers will occur on the
+  When default "connection" value is set, a dedicated socket will be allocated
-  shared listener socket. This option can be a good compromise for small
+  by every QUIC connections. This option is the preferred one to achieve the
-  traffic as it allows to reduce FD consumption. However, performance won't be
+  best performance with a large QUIC traffic. However, this relies on some
-  optimal due to a higher CPU usage if listeners are shared accross a lot of
+  advanced features from the UDP network stack. If your platform is deemed not
-  threads or a large number of QUIC connections can be used simultaneously.
+  compatible, haproxy will automatically switch to "listener" mode on startup.
 
-  If "connection" value is set, a dedicated socket will be allocated by every
+  The "listener" value indicates that QUIC transfers will occur on the shared
-  QUIC connections. This option is the preferred one to achieve the best
+  listener socket. This option can be a good compromise for small traffic as it
-  performance with a large QUIC traffic. However, this relies on some advanced
+  allows to reduce FD consumption. However, performance won't be optimal due to
-  features from the UDP network stack. If your platform is deemed not
+  a higher CPU usage if listeners are shared accross a lot of threads or a
-  compatible, haproxy will automatically revert to "listener" mode on startup.
+  large number of QUIC connections can be used simultaneously.
 
 tune.rcvbuf.client <number>
 tune.rcvbuf.server <number>
@@ -4622,13 +4622,13 @@ bind /<path> [, ...] [param*]
                       to receive a FD over the unix socket and uses it as if it
                       was the FD of an accept(). Should be used carefully.
                     - 'quic4@' -> address is resolved as IPv4 and protocol UDP
-                      is used. Note that by default QUIC connections attached
+                      is used. Note that to achieve the best performance with a
-                      to a listener will be multiplexed over the listener
+                      large traffic you should keep "tune.quic.conn-owner" on
-                      socket. With a large traffic this has a noticeable impact
+                      connection. Else QUIC connections will be multiplexed
-                      on performance and CPU consumption. To improve this, you
+                      over the listener socket. Another alternative would be to
-                      can change default settings of "tune.quic.conn-owner" to
+                      duplicate QUIC listener instances over several threads,
-                      connection or at least duplicate QUIC listener instances
+                      for example using "shards" keyword to at least reduce
-                      over several threads, for example using "shards" keyword.
+                      thread contention.
                     - 'quic6@' -> address is resolved as IPv6 and protocol UDP
                       is used. The performance note for QUIC over IPv4 applies
                       as well.

src/haproxy.c

@@ -1577,6 +1577,9 @@ static void init_args(int argc, char **argv)
 #endif
 #ifdef USE_THREAD
 	global.tune.options |= GTUNE_IDLE_POOL_SHARED;
+#endif
+#ifdef USE_QUIC
+	global.tune.options |= GTUNE_QUIC_SOCK_PER_CONN;
 #endif
 	global.tune.options |= GTUNE_STRICT_LIMITS;