rxrpc: Delay terminal ACK transmission on a client call

Delay terminal ACK transmission on a client call by deferring it to the
connection processor.  This allows it to be skipped if we can send the next
call instead, the first DATA packet of which will implicitly ack this call.

Signed-off-by: David Howells <dhowells@redhat.com>

1 files changed, 18 insertions, 0 deletions

diff --git a/net/rxrpc/conn_client.c b/net/rxrpc/conn_client.c
index 5f9624bd311c..cfb997593da9 100644
--- a/net/rxrpc/conn_client.c
+++ b/net/rxrpc/conn_client.c
@@ -554,6 +554,11 @@ static void rxrpc_activate_one_channel(struct rxrpc_connection *conn,
 
 	trace_rxrpc_client(conn, channel, rxrpc_client_chan_activate);
 
+	/* Cancel the final ACK on the previous call if it hasn't been sent yet
+	 * as the DATA packet will implicitly ACK it.
+	 */
+	clear_bit(RXRPC_CONN_FINAL_ACK_0 + channel, &conn->flags);
+
 	write_lock_bh(&call->state_lock);
 	if (!test_bit(RXRPC_CALL_TX_LASTQ, &call->flags))
 		call->state = RXRPC_CALL_CLIENT_SEND_REQUEST;
@@ -813,6 +818,19 @@ void rxrpc_disconnect_client_call(struct rxrpc_call *call)
 		goto out_2;
 	}
 
+	/* Schedule the final ACK to be transmitted in a short while so that it
+	 * can be skipped if we find a follow-on call.  The first DATA packet
+	 * of the follow on call will implicitly ACK this call.
+	 */
+	if (test_bit(RXRPC_CALL_EXPOSED, &call->flags)) {
+		unsigned long final_ack_at = jiffies + 2;
+
+		WRITE_ONCE(chan->final_ack_at, final_ack_at);
+		smp_wmb(); /* vs rxrpc_process_delayed_final_acks() */
+		set_bit(RXRPC_CONN_FINAL_ACK_0 + channel, &conn->flags);
+		rxrpc_reduce_conn_timer(conn, final_ack_at);
+	}
+
 	/* Things are more complex and we need the cache lock.  We might be
 	 * able to simply idle the conn or it might now be lurking on the wait
 	 * list.  It might even get moved back to the active list whilst we're