linux-kernel - [PATCH net 5/5] rxrpc: Request an ACK on impending Tx stall

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Date: Fri,  3 May 2024 16:07:43 +0100
From: David Howells <dhowells@...hat.com>
To: netdev@...r.kernel.org
Cc: David Howells <dhowells@...hat.com>,
	Marc Dionne <marc.dionne@...istor.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>,
	linux-afs@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH net 5/5] rxrpc: Request an ACK on impending Tx stall

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.

Fixes: 17926a79320a ("[AF_RXRPC]: Provide secure RxRPC sockets for use by userspace and kernel both")
Signed-off-by: David Howells <dhowells@...hat.com>
cc: Marc Dionne <marc.dionne@...istor.com>
cc: "David S. Miller" <davem@...emloft.net>
cc: Eric Dumazet <edumazet@...gle.com>
cc: Jakub Kicinski <kuba@...nel.org>
cc: Paolo Abeni <pabeni@...hat.com>
cc: linux-afs@...ts.infradead.org
cc: netdev@...r.kernel.org
---
 include/trace/events/rxrpc.h | 1 +
 net/rxrpc/ar-internal.h      | 2 +-
 net/rxrpc/output.c           | 2 ++
 net/rxrpc/proc.c             | 5 +++--
 4 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/include/trace/events/rxrpc.h b/include/trace/events/rxrpc.h
index 7b6c1db53401..dca9f4759dcb 100644
--- a/include/trace/events/rxrpc.h
+++ b/include/trace/events/rxrpc.h
@@ -449,6 +449,7 @@
 
 #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 c11a6043c8f2..08de24658f4f 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 4ebd0bd40a02..32626ff377e1 100644
--- a/net/rxrpc/output.c
+++ b/net/rxrpc/output.c
@@ -372,6 +372,8 @@ 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 (!more && !last)
+		why = rxrpc_reqack_app_stall;
 	else
 		goto dont_set_request_ack;
 
diff --git a/net/rxrpc/proc.c b/net/rxrpc/proc.c
index 3b7e34dd4385..1bab7f5a7d0f 100644
--- a/net/rxrpc/proc.c
+++ b/net/rxrpc/proc.c
@@ -519,10 +519,11 @@ int rxrpc_stats_show(struct seq_file *seq, void *v)
 		   atomic_read(&rxnet->stat_rx_acks[RXRPC_ACK_DELAY]),
 		   atomic_read(&rxnet->stat_rx_acks[RXRPC_ACK_IDLE]));
 	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]),