From: Susant Sahani Date: Thu, 14 Aug 2014 17:36:12 +0000 (+0530) Subject: socket: Add support for TCP defer accept X-Git-Tag: v216~103 X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~ianmdlvl/git?p=elogind.git;a=commitdiff_plain;h=cc567c9beace114554f7e7f50c3a5181cc44a07d socket: Add support for TCP defer accept TCP_DEFER_ACCEPT Allow a listener to be awakened only when data arrives on the socket. If TCP_DEFER_ACCEPT set on a server-side listening socket, the TCP/IP stack will not to wait for the final ACK packet and not to initiate the process until the first packet of real data has arrived. After sending the SYN/ACK, the server will then wait for a data packet from a client. Now, only three packets will be sent over the network, and the connection establishment delay will be significantly reduced. --- diff --git a/man/systemd.socket.xml b/man/systemd.socket.xml index 5efb398b0..448390583 100644 --- a/man/systemd.socket.xml +++ b/man/systemd.socket.xml @@ -545,6 +545,47 @@ for details.). + + DeferAccept= + + Takes time (in + seconds) as argument. If set, the + listening process will be awakened + only when data arrives on the socket, + and not immediately when connection is + established. When this option is set, + the + TCP_DEFER_ACCEPT + socket option will be used (see + tcp7), + and the kernel will ignore initial ACK + packets without any data. The argument + specifies the approximate amount of + time the kernel should wait for + incoming data before falling back to + the normal behaviour of honouring + empty ACK packets. This option is + beneficial for protocols where the + client sends the data first (e.g. + HTTP, in contrast to SMTP), because + the server process will not be woken + up unnecessarily before it can take + any action. + + + If the client also uses the + TCP_DEFER_ACCEPT + option, the latency of the initial + connection may be reduced, because the + kernel will send data in the final + packet establishing the connection + (the third packet in the "three-way + handshake"). + + Disabled by default. + + + ReceiveBuffer= SendBuffer= diff --git a/src/core/dbus-socket.c b/src/core/dbus-socket.c index bdf111c9e..cc55b8d71 100644 --- a/src/core/dbus-socket.c +++ b/src/core/dbus-socket.c @@ -100,6 +100,7 @@ const sd_bus_vtable bus_socket_vtable[] = { SD_BUS_PROPERTY("KeepAliveTime", "t", bus_property_get_usec, offsetof(Socket, keep_alive_time), SD_BUS_VTABLE_PROPERTY_CONST), SD_BUS_PROPERTY("KeepAliveInterval", "t", bus_property_get_usec, offsetof(Socket, keep_alive_interval), SD_BUS_VTABLE_PROPERTY_CONST), SD_BUS_PROPERTY("KeepAliveProbes", "u", bus_property_get_unsigned, offsetof(Socket, keep_alive_cnt), SD_BUS_VTABLE_PROPERTY_CONST), + SD_BUS_PROPERTY("DeferAccept" , "t", bus_property_get_usec, offsetof(Socket, defer_accept), SD_BUS_VTABLE_PROPERTY_CONST), SD_BUS_PROPERTY("Priority", "i", bus_property_get_int, offsetof(Socket, priority), SD_BUS_VTABLE_PROPERTY_CONST), SD_BUS_PROPERTY("ReceiveBuffer", "t", bus_property_get_size, offsetof(Socket, receive_buffer), SD_BUS_VTABLE_PROPERTY_CONST), SD_BUS_PROPERTY("SendBuffer", "t", bus_property_get_size, offsetof(Socket, send_buffer), SD_BUS_VTABLE_PROPERTY_CONST), diff --git a/src/core/load-fragment-gperf.gperf.m4 b/src/core/load-fragment-gperf.gperf.m4 index 67bd0e520..b4e2b2574 100644 --- a/src/core/load-fragment-gperf.gperf.m4 +++ b/src/core/load-fragment-gperf.gperf.m4 @@ -234,6 +234,7 @@ Socket.KeepAlive, config_parse_bool, 0, Socket.KeepAliveTime, config_parse_sec, 0, offsetof(Socket, keep_alive_time) Socket.KeepAliveInterval, config_parse_sec, 0, offsetof(Socket, keep_alive_interval) Socket.KeepAliveProbes, config_parse_unsigned, 0, offsetof(Socket, keep_alive_cnt) +Socket.DeferAccept, config_parse_sec, 0, offsetof(Socket, defer_accept) Socket.NoDelay, config_parse_bool, 0, offsetof(Socket, no_delay) Socket.Priority, config_parse_int, 0, offsetof(Socket, priority) Socket.ReceiveBuffer, config_parse_iec_size, 0, offsetof(Socket, receive_buffer) diff --git a/src/core/socket.c b/src/core/socket.c index d6d9821f5..a16b20d73 100644 --- a/src/core/socket.c +++ b/src/core/socket.c @@ -613,6 +613,12 @@ static void socket_dump(Unit *u, FILE *f, const char *prefix) { "%sKeepAliveProbes: %u\n", prefix, s->keep_alive_cnt); + if(s->defer_accept) + fprintf(f, + "%sDeferAccept: %s\n", + prefix, format_timespan(time_string, FORMAT_TIMESPAN_MAX, + s->defer_accept, USEC_PER_SEC)); + LIST_FOREACH(port, p, s->ports) { if (p->type == SOCKET_SOCKET) { @@ -828,6 +834,12 @@ static void socket_apply_socket_options(Socket *s, int fd) { log_warning_unit(UNIT(s)->id, "TCP_KEEPCNT failed: %m"); } + if (s->defer_accept) { + int value = s->defer_accept / USEC_PER_SEC; + if (setsockopt(fd, SOL_TCP, TCP_DEFER_ACCEPT, &value, sizeof(value)) < 0) + log_warning_unit(UNIT(s)->id, "TCP_DEFER_ACCEPT failed: %m"); + } + if (s->no_delay) { int b = s->no_delay; if (setsockopt(fd, SOL_TCP, TCP_NODELAY, &b, sizeof(b)) < 0) diff --git a/src/core/socket.h b/src/core/socket.h index 8871eb1ca..eede70564 100644 --- a/src/core/socket.h +++ b/src/core/socket.h @@ -105,6 +105,7 @@ struct Socket { usec_t timeout_usec; usec_t keep_alive_time; usec_t keep_alive_interval; + usec_t defer_accept; ExecCommand* exec_command[_SOCKET_EXEC_COMMAND_MAX]; ExecContext exec_context;