[PATCH 12/18] drbd: trigger tcp_push_pending_frames() for PING and PING_ACK

[Philipp Reisner <philipp.reisner@linbit.com>]

From: Lars Ellenberg <lars.ellenberg@linbit.com>

This should reduce latency for such in-DRBD-protocol "pings",
and may help reduce spurious disconnect/reconnect cycles due to
 "PingAck did not arrive in time."

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>
---
 drivers/block/drbd/drbd_main.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/block/drbd/drbd_main.c b/drivers/block/drbd/drbd_main.c
index 8e0813d..77d34a6 100644
--- a/drivers/block/drbd/drbd_main.c
+++ b/drivers/block/drbd/drbd_main.c
@@ -662,6 +662,11 @@ static int __send_command(struct drbd_connection *connection, int vnr,
 			    msg_flags);
 	if (data && !err)
 		err = drbd_send_all(connection, sock->socket, data, size, 0);
+	/* DRBD protocol "pings" are latency critical.
+	 * This is supposed to trigger tcp_push_pending_frames() */
+	if (!err && (cmd == P_PING || cmd == P_PING_ACK))
+		drbd_tcp_nodelay(sock->socket);
+
 	return err;
 }
 
-- 
1.9.1