linux-kernel - [PATCH net 2/5] rxrpc: Only transmit one ACK per jumbo packet received

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Date: Fri,  3 May 2024 16:07:40 +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 2/5] rxrpc: Only transmit one ACK per jumbo packet received

Only generate one ACK packet for all the subpackets in a jumbo packet.  If
we would like to generate more than one ACK, we prioritise them base on
their reason code, in the order, highest first:

   OutOfSeq > NoSpace > ExceedsWin > Duplicate > Requested > Delay > Idle

For the first four, we reference the lowest offending subpacket; for the
last three, the highest.

This reduces the number of ACKs we end up transmitting to one per UDP
packet transmitted to reduce network loading and packet parsing.

Fixes: 5d7edbc9231e ("rxrpc: Get rid of the Rx ring")
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
---
 net/rxrpc/input.c | 46 +++++++++++++++++++++++++++++++++++-----------
 1 file changed, 35 insertions(+), 11 deletions(-)

diff --git a/net/rxrpc/input.c b/net/rxrpc/input.c
index 860075f1290b..16d49a861dbb 100644
--- a/net/rxrpc/input.c
+++ b/net/rxrpc/input.c
@@ -9,6 +9,17 @@
 
 #include "ar-internal.h"
 
+/* Override priority when generating ACKs for received DATA */
+static const u8 rxrpc_ack_priority[RXRPC_ACK__INVALID] = {
+	[RXRPC_ACK_IDLE]		= 1,
+	[RXRPC_ACK_DELAY]		= 2,
+	[RXRPC_ACK_REQUESTED]		= 3,
+	[RXRPC_ACK_DUPLICATE]		= 4,
+	[RXRPC_ACK_EXCEEDS_WINDOW]	= 5,
+	[RXRPC_ACK_NOSPACE]		= 6,
+	[RXRPC_ACK_OUT_OF_SEQUENCE]	= 7,
+};
+
 static void rxrpc_proto_abort(struct rxrpc_call *call, rxrpc_seq_t seq,
 			      enum rxrpc_abort_reason why)
 {
@@ -365,7 +376,7 @@ static void rxrpc_input_queue_data(struct rxrpc_call *call, struct sk_buff *skb,
  * Process a DATA packet.
  */
 static void rxrpc_input_data_one(struct rxrpc_call *call, struct sk_buff *skb,
-				 bool *_notify)
+				 bool *_notify, rxrpc_serial_t *_ack_serial, int *_ack_reason)
 {
 	struct rxrpc_skb_priv *sp = rxrpc_skb(skb);
 	struct sk_buff *oos;
@@ -418,8 +429,6 @@ static void rxrpc_input_data_one(struct rxrpc_call *call, struct sk_buff *skb,
 		/* Send an immediate ACK if we fill in a hole */
 		else if (!skb_queue_empty(&call->rx_oos_queue))
 			ack_reason = RXRPC_ACK_DELAY;
-		else
-			call->ackr_nr_unacked++;
 
 		window++;
 		if (after(window, wtop)) {
@@ -497,12 +506,16 @@ static void rxrpc_input_data_one(struct rxrpc_call *call, struct sk_buff *skb,
 	}
 
 send_ack:
-	if (ack_reason >= 0)
-		rxrpc_send_ACK(call, ack_reason, serial,
-			       rxrpc_propose_ack_input_data);
-	else
-		rxrpc_propose_delay_ACK(call, serial,
-					rxrpc_propose_ack_input_data);
+	if (ack_reason >= 0) {
+		if (rxrpc_ack_priority[ack_reason] > rxrpc_ack_priority[*_ack_reason]) {
+			*_ack_serial = serial;
+			*_ack_reason = ack_reason;
+		} else if (rxrpc_ack_priority[ack_reason] == rxrpc_ack_priority[*_ack_reason] &&
+			   ack_reason == RXRPC_ACK_REQUESTED) {
+			*_ack_serial = serial;
+			*_ack_reason = ack_reason;
+		}
+	}
 }
 
 /*
@@ -513,9 +526,11 @@ static bool rxrpc_input_split_jumbo(struct rxrpc_call *call, struct sk_buff *skb
 	struct rxrpc_jumbo_header jhdr;
 	struct rxrpc_skb_priv *sp = rxrpc_skb(skb), *jsp;
 	struct sk_buff *jskb;
+	rxrpc_serial_t ack_serial = 0;
 	unsigned int offset = sizeof(struct rxrpc_wire_header);
 	unsigned int len = skb->len - offset;
 	bool notify = false;
+	int ack_reason = 0;
 
 	while (sp->hdr.flags & RXRPC_JUMBO_PACKET) {
 		if (len < RXRPC_JUMBO_SUBPKTLEN)
@@ -535,7 +550,7 @@ static bool rxrpc_input_split_jumbo(struct rxrpc_call *call, struct sk_buff *skb
 		jsp = rxrpc_skb(jskb);
 		jsp->offset = offset;
 		jsp->len = RXRPC_JUMBO_DATALEN;
-		rxrpc_input_data_one(call, jskb, &notify);
+		rxrpc_input_data_one(call, jskb, &notify, &ack_serial, &ack_reason);
 		rxrpc_free_skb(jskb, rxrpc_skb_put_jumbo_subpacket);
 
 		sp->hdr.flags = jhdr.flags;
@@ -548,7 +563,16 @@ static bool rxrpc_input_split_jumbo(struct rxrpc_call *call, struct sk_buff *skb
 
 	sp->offset = offset;
 	sp->len    = len;
-	rxrpc_input_data_one(call, skb, &notify);
+	rxrpc_input_data_one(call, skb, &notify, &ack_serial, &ack_reason);
+
+	if (ack_reason > 0) {
+		rxrpc_send_ACK(call, ack_reason, ack_serial,
+			       rxrpc_propose_ack_input_data);
+	} else {
+		call->ackr_nr_unacked++;
+		rxrpc_propose_delay_ACK(call, sp->hdr.serial,
+					rxrpc_propose_ack_input_data);
+	}
 	if (notify) {
 		trace_rxrpc_notify_socket(call->debug_id, sp->hdr.serial);
 		rxrpc_notify_socket(call);