[PATCH net-next v2 07/39] rxrpc: Request an ACK on impending Tx stall

[David Howells <dhowells@redhat.com>]

Set the REQUEST-ACK flag on the DATA packet we're about to send if we're
about to stall transmission because the app layer isn't keeping up
supplying us with data to transmit.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: "David S. Miller" <davem@davemloft.net>
cc: Eric Dumazet <edumazet@google.com>
cc: Jakub Kicinski <kuba@kernel.org>
cc: Paolo Abeni <pabeni@redhat.com>
cc: linux-afs@lists.infradead.org
cc: netdev@vger.kernel.org
---
 include/trace/events/rxrpc.h | 1 +
 net/rxrpc/ar-internal.h      | 2 +-
 net/rxrpc/output.c           | 7 ++++++-
 net/rxrpc/proc.c             | 5 +++--
 4 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/include/trace/events/rxrpc.h b/include/trace/events/rxrpc.h
index 62064f63d6eb..d86b5f07d292 100644
--- a/include/trace/events/rxrpc.h
+++ b/include/trace/events/rxrpc.h
@@ -452,6 +452,7 @@
 
 #define rxrpc_req_ack_traces \
 	EM(rxrpc_reqack_ack_lost,		"ACK-LOST  ")	\
+	EM(rxrpc_reqack_app_stall,		"APP-STALL ")	\
 	EM(rxrpc_reqack_more_rtt,		"MORE-RTT  ")	\
 	EM(rxrpc_reqack_no_srv_last,		"NO-SRVLAST")	\
 	EM(rxrpc_reqack_old_rtt,		"OLD-RTT   ")	\
diff --git a/net/rxrpc/ar-internal.h b/net/rxrpc/ar-internal.h
index fcdfbc1d5aaf..d0fd37bdcfe9 100644
--- a/net/rxrpc/ar-internal.h
+++ b/net/rxrpc/ar-internal.h
@@ -110,7 +110,7 @@ struct rxrpc_net {
 	atomic_t		stat_tx_acks[256];
 	atomic_t		stat_rx_acks[256];
 
-	atomic_t		stat_why_req_ack[7];
+	atomic_t		stat_why_req_ack[8];
 
 	atomic_t		stat_io_loop;
 };
diff --git a/net/rxrpc/output.c b/net/rxrpc/output.c
index 50d5f2a02458..b93a5d50be3e 100644
--- a/net/rxrpc/output.c
+++ b/net/rxrpc/output.c
@@ -330,7 +330,7 @@ static void rxrpc_prepare_data_subpacket(struct rxrpc_call *call, struct rxrpc_t
 	struct rxrpc_wire_header *whdr = txb->kvec[0].iov_base;
 	enum rxrpc_req_ack_trace why;
 	struct rxrpc_connection *conn = call->conn;
-	bool last;
+	bool last, more;
 	u8 flags;
 
 	_enter("%x,{%d}", txb->seq, txb->len);
@@ -345,6 +345,9 @@ static void rxrpc_prepare_data_subpacket(struct rxrpc_call *call, struct rxrpc_t
 	flags = txb->flags & RXRPC_TXBUF_WIRE_FLAGS;
 	last = txb->flags & RXRPC_LAST_PACKET;
 
+	more = (!list_is_last(&txb->call_link, &call->tx_buffer) ||
+		!list_empty(&call->tx_sendmsg));
+
 	/* If our RTT cache needs working on, request an ACK.  Also request
 	 * ACKs if a DATA packet appears to have been lost.
 	 *
@@ -366,6 +369,8 @@ static void rxrpc_prepare_data_subpacket(struct rxrpc_call *call, struct rxrpc_t
 		why = rxrpc_reqack_more_rtt;
 	else if (ktime_before(ktime_add_ms(call->peer->rtt_last_req, 1000), ktime_get_real()))
 		why = rxrpc_reqack_old_rtt;
+	else if (!last && !more)
+		why = rxrpc_reqack_app_stall;
 	else
 		goto dont_set_request_ack;
 
diff --git a/net/rxrpc/proc.c b/net/rxrpc/proc.c
index cdf32f0d8e0e..ce4d48bdfbe9 100644
--- a/net/rxrpc/proc.c
+++ b/net/rxrpc/proc.c
@@ -520,10 +520,11 @@ int rxrpc_stats_show(struct seq_file *seq, void *v)
 		   atomic_read(&rxnet->stat_rx_acks[RXRPC_ACK_IDLE]),
 		   atomic_read(&rxnet->stat_rx_acks[0]));
 	seq_printf(seq,
-		   "Why-Req-A: acklost=%u mrtt=%u ortt=%u\n",
+		   "Why-Req-A: acklost=%u mrtt=%u ortt=%u stall=%u\n",
 		   atomic_read(&rxnet->stat_why_req_ack[rxrpc_reqack_ack_lost]),
 		   atomic_read(&rxnet->stat_why_req_ack[rxrpc_reqack_more_rtt]),
-		   atomic_read(&rxnet->stat_why_req_ack[rxrpc_reqack_old_rtt]));
+		   atomic_read(&rxnet->stat_why_req_ack[rxrpc_reqack_old_rtt]),
+		   atomic_read(&rxnet->stat_why_req_ack[rxrpc_reqack_app_stall]));
 	seq_printf(seq,
 		   "Why-Req-A: nolast=%u retx=%u slows=%u smtxw=%u\n",
 		   atomic_read(&rxnet->stat_why_req_ack[rxrpc_reqack_no_srv_last]),