rxrpc: Send an ACK after every few DATA packets we receive

Send an ACK if we haven't sent one for the last two packets we've received.
This keeps the other end apprised of where we've got to - which is
important if they're doing slow-start.

We do this in recvmsg so that we can dispatch a packet directly without the
need to wake up the background thread.

This should possibly be made configurable in future.

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

4 files changed, 33 insertions, 9 deletions

diff --git a/net/rxrpc/ar-internal.h b/net/rxrpc/ar-internal.h
index 042dbcc52654..e3bf9c0e3ad1 100644
--- a/net/rxrpc/ar-internal.h
+++ b/net/rxrpc/ar-internal.h
@@ -533,6 +533,8 @@ struct rxrpc_call {
 	u16			ackr_skew;	/* skew on packet being ACK'd */
 	rxrpc_serial_t		ackr_serial;	/* serial of packet being ACK'd */
 	rxrpc_seq_t		ackr_prev_seq;	/* previous sequence number received */
+	rxrpc_seq_t		ackr_consumed;	/* Highest packet shown consumed */
+	rxrpc_seq_t		ackr_seen;	/* Highest packet shown seen */
 	rxrpc_serial_t		ackr_ping;	/* Last ping sent */
 	ktime_t			ackr_ping_time;	/* Time last ping sent */
 
@@ -695,6 +697,7 @@ enum rxrpc_propose_ack_trace {
 	rxrpc_propose_ack_respond_to_ack,
 	rxrpc_propose_ack_respond_to_ping,
 	rxrpc_propose_ack_retry_tx,
+	rxrpc_propose_ack_rotate_rx,
 	rxrpc_propose_ack_terminal_ack,
 	rxrpc_propose_ack__nr_trace
 };
diff --git a/net/rxrpc/misc.c b/net/rxrpc/misc.c
index 1ca14835d87f..a473fd7dabaa 100644
--- a/net/rxrpc/misc.c
+++ b/net/rxrpc/misc.c
@@ -202,6 +202,7 @@ const char rxrpc_propose_ack_traces[rxrpc_propose_ack__nr_trace][8] = {
 	[rxrpc_propose_ack_respond_to_ack]	= "Rsp2Ack",
 	[rxrpc_propose_ack_respond_to_ping]	= "Rsp2Png",
 	[rxrpc_propose_ack_retry_tx]		= "RetryTx",
+	[rxrpc_propose_ack_rotate_rx]		= "RxAck  ",
 	[rxrpc_propose_ack_terminal_ack]	= "ClTerm ",
 };
 
diff --git a/net/rxrpc/output.c b/net/rxrpc/output.c
index 0c563e325c9d..3eb01445e814 100644
--- a/net/rxrpc/output.c
+++ b/net/rxrpc/output.c
@@ -36,7 +36,9 @@ struct rxrpc_pkt_buffer {
  * Fill out an ACK packet.
  */
 static size_t rxrpc_fill_out_ack(struct rxrpc_call *call,
-				 struct rxrpc_pkt_buffer *pkt)
+				 struct rxrpc_pkt_buffer *pkt,
+				 rxrpc_seq_t *_hard_ack,
+				 rxrpc_seq_t *_top)
 {
 	rxrpc_serial_t serial;
 	rxrpc_seq_t hard_ack, top, seq;
@@ -48,6 +50,8 @@ static size_t rxrpc_fill_out_ack(struct rxrpc_call *call,
 	serial = call->ackr_serial;
 	hard_ack = READ_ONCE(call->rx_hard_ack);
 	top = smp_load_acquire(&call->rx_top);
+	*_hard_ack = hard_ack;
+	*_top = top;
 
 	pkt->ack.bufferSpace	= htons(8);
 	pkt->ack.maxSkew	= htons(call->ackr_skew);
@@ -96,6 +100,7 @@ int rxrpc_send_call_packet(struct rxrpc_call *call, u8 type)
 	struct msghdr msg;
 	struct kvec iov[2];
 	rxrpc_serial_t serial;
+	rxrpc_seq_t hard_ack, top;
 	size_t len, n;
 	bool ping = false;
 	int ioc, ret;
@@ -146,7 +151,7 @@ int rxrpc_send_call_packet(struct rxrpc_call *call, u8 type)
 			goto out;
 		}
 		ping = (call->ackr_reason == RXRPC_ACK_PING);
-		n = rxrpc_fill_out_ack(call, pkt);
+		n = rxrpc_fill_out_ack(call, pkt, &hard_ack, &top);
 		call->ackr_reason = 0;
 
 		spin_unlock_bh(&call->lock);
@@ -203,18 +208,22 @@ int rxrpc_send_call_packet(struct rxrpc_call *call, u8 type)
 	if (ping)
 		call->ackr_ping_time = ktime_get_real();
 
-	if (ret < 0 && call->state < RXRPC_CALL_COMPLETE) {
-		switch (type) {
-		case RXRPC_PACKET_TYPE_ACK:
+	if (type == RXRPC_PACKET_TYPE_ACK &&
+	    call->state < RXRPC_CALL_COMPLETE) {
+		if (ret < 0) {
 			clear_bit(RXRPC_CALL_PINGING, &call->flags);
 			rxrpc_propose_ACK(call, pkt->ack.reason,
 					  ntohs(pkt->ack.maxSkew),
 					  ntohl(pkt->ack.serial),
 					  true, true,
 					  rxrpc_propose_ack_retry_tx);
-			break;
-		case RXRPC_PACKET_TYPE_ABORT:
-			break;
+		} else {
+			spin_lock_bh(&call->lock);
+			if (after(hard_ack, call->ackr_consumed))
+				call->ackr_consumed = hard_ack;
+			if (after(top, call->ackr_seen))
+				call->ackr_seen = top;
+			spin_unlock_bh(&call->lock);
 		}
 	}
 
diff --git a/net/rxrpc/recvmsg.c b/net/rxrpc/recvmsg.c
index 8c7f3de45bac..a7458c398b9e 100644
--- a/net/rxrpc/recvmsg.c
+++ b/net/rxrpc/recvmsg.c
@@ -201,8 +201,19 @@ static void rxrpc_rotate_rx_window(struct rxrpc_call *call)
 
 	_debug("%u,%u,%02x", hard_ack, top, flags);
 	trace_rxrpc_receive(call, rxrpc_receive_rotate, serial, hard_ack);
-	if (flags & RXRPC_LAST_PACKET)
+	if (flags & RXRPC_LAST_PACKET) {
 		rxrpc_end_rx_phase(call);
+	} else {
+		/* Check to see if there's an ACK that needs sending. */
+		if (after_eq(hard_ack, call->ackr_consumed + 2) ||
+		    after_eq(top, call->ackr_seen + 2) ||
+		    (hard_ack == top && after(hard_ack, call->ackr_consumed)))
+			rxrpc_propose_ACK(call, RXRPC_ACK_DELAY, 0, serial,
+					  true, false,
+					  rxrpc_propose_ack_rotate_rx);
+		if (call->ackr_reason)
+			rxrpc_send_call_packet(call, RXRPC_PACKET_TYPE_ACK);
+	}
 }
 
 /*