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authorSusant Sahani <susant@redhat.com>2014-08-14 23:06:12 +0530
committerZbigniew Jędrzejewski-Szmek <zbyszek@in.waw.pl>2014-08-14 19:55:44 -0400
commitcc567c9beace114554f7e7f50c3a5181cc44a07d (patch)
tree749ee36446a80a0ad710c73f7677c3719fbbb277
parent209e9dcd7b2f23b68ff93bf20fad025bc03219ac (diff)
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.
-rw-r--r--man/systemd.socket.xml41
-rw-r--r--src/core/dbus-socket.c1
-rw-r--r--src/core/load-fragment-gperf.gperf.m41
-rw-r--r--src/core/socket.c12
-rw-r--r--src/core/socket.h1
5 files changed, 56 insertions, 0 deletions
diff --git a/man/systemd.socket.xml b/man/systemd.socket.xml
index 5efb398b09..4483905832 100644
--- a/man/systemd.socket.xml
+++ b/man/systemd.socket.xml
@@ -546,6 +546,47 @@
</varlistentry>
<varlistentry>
+ <term><varname>DeferAccept=</varname></term>
+
+ <listitem><para>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
+ <constant>TCP_DEFER_ACCEPT</constant>
+ socket option will be used (see
+ <citerefentry><refentrytitle>tcp</refentrytitle><manvolnum>7</manvolnum></citerefentry>),
+ 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.
+ </para>
+
+ <para>If the client also uses the
+ <constant>TCP_DEFER_ACCEPT</constant>
+ 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").</para>
+
+ <para>Disabled by default.</para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
<term><varname>ReceiveBuffer=</varname></term>
<term><varname>SendBuffer=</varname></term>
<listitem><para>Takes an integer
diff --git a/src/core/dbus-socket.c b/src/core/dbus-socket.c
index bdf111c9e3..cc55b8d71b 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 67bd0e5209..b4e2b25743 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 d6d9821f57..a16b20d739 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 8871eb1ca3..eede70564a 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;