rxrpc: Generate extra pings for RTT during heavy-receive call

When doing a call that has a single transmitted data packet and a massive
amount of received data packets, we only ping for one RTT sample, which
means we don't get a good reading on it.

Fix this by converting occasional IDLE ACKs into PING ACKs to elicit a
response.
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: linux-afs@lists.infradead.org

include/trace/events/rxrpc.h

@@ -360,11 +360,12 @@
 	EM(rxrpc_propose_ack_client_tx_end,	"ClTxEnd") \
 	EM(rxrpc_propose_ack_input_data,	"DataIn ") \
 	EM(rxrpc_propose_ack_input_data_hole,	"DataInH") \
-	EM(rxrpc_propose_ack_ping_for_check_life, "ChkLife") \
 	EM(rxrpc_propose_ack_ping_for_keepalive, "KeepAlv") \
 	EM(rxrpc_propose_ack_ping_for_lost_ack,	"LostAck") \
 	EM(rxrpc_propose_ack_ping_for_lost_reply, "LostRpl") \
+	EM(rxrpc_propose_ack_ping_for_old_rtt,	"OldRtt ") \
 	EM(rxrpc_propose_ack_ping_for_params,	"Params ") \
+	EM(rxrpc_propose_ack_ping_for_rtt,	"Rtt    ") \
 	EM(rxrpc_propose_ack_processing_op,	"ProcOp ") \
 	EM(rxrpc_propose_ack_respond_to_ack,	"Rsp2Ack") \
 	EM(rxrpc_propose_ack_respond_to_ping,	"Rsp2Png") \

net/rxrpc/call_event.c

@@ -498,9 +498,18 @@ bool rxrpc_input_call_event(struct rxrpc_call *call, struct sk_buff *skb)
 		rxrpc_send_ACK(call, RXRPC_ACK_IDLE, 0,
 			       rxrpc_propose_ack_rx_idle);
 
-	if (atomic_read(&call->ackr_nr_unacked) > 2)
-		rxrpc_send_ACK(call, RXRPC_ACK_IDLE, 0,
-			       rxrpc_propose_ack_input_data);
+	if (atomic_read(&call->ackr_nr_unacked) > 2) {
+		if (call->peer->rtt_count < 3)
+			rxrpc_send_ACK(call, RXRPC_ACK_PING, 0,
+				       rxrpc_propose_ack_ping_for_rtt);
+		else if (ktime_before(ktime_add_ms(call->peer->rtt_last_req, 1000),
+				      ktime_get_real()))
+			rxrpc_send_ACK(call, RXRPC_ACK_PING, 0,
+				       rxrpc_propose_ack_ping_for_old_rtt);
+		else
+			rxrpc_send_ACK(call, RXRPC_ACK_IDLE, 0,
+				       rxrpc_propose_ack_input_data);
+	}
 
 	/* Make sure the timer is restarted */
 	if (!__rxrpc_call_is_complete(call)) {

net/rxrpc/output.c

@@ -253,12 +253,15 @@ int rxrpc_send_ack_packet(struct rxrpc_call *call, struct rxrpc_txbuf *txb)
 	iov_iter_kvec(&msg.msg_iter, WRITE, iov, 1, len);
 	ret = do_udp_sendmsg(conn->local->socket, &msg, len);
 	call->peer->last_tx_at = ktime_get_seconds();
-	if (ret < 0)
+	if (ret < 0) {
 		trace_rxrpc_tx_fail(call->debug_id, serial, ret,
 				    rxrpc_tx_point_call_ack);
-	else
+	} else {
 		trace_rxrpc_tx_packet(call->debug_id, &txb->wire,
 				      rxrpc_tx_point_call_ack);
+		if (txb->wire.flags & RXRPC_REQUEST_ACK)
+			call->peer->rtt_last_req = ktime_get_real();
+	}
 	rxrpc_tx_backoff(call, ret);
 
 	if (!__rxrpc_call_is_complete(call)) {