Patch "rxrpc: Only transmit one ACK per jumbo packet received" has been added to the 6.8-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    rxrpc: Only transmit one ACK per jumbo packet received

to the 6.8-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     rxrpc-only-transmit-one-ack-per-jumbo-packet-receive.patch
and it can be found in the queue-6.8 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit f97a93c791329d60aac48e7955a64028bc75aed5
Author: David Howells <dhowells@xxxxxxxxxx>
Date:   Fri May 3 16:07:40 2024 +0100

    rxrpc: Only transmit one ACK per jumbo packet received
    
    [ Upstream commit 012b7206918dcc5a4dcf1432b3e643114c95957e ]
    
    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@xxxxxxxxxx>
    cc: Marc Dionne <marc.dionne@xxxxxxxxxxxx>
    cc: linux-afs@xxxxxxxxxxxxxxxxxxx
    Reviewed-by: Jeffrey Altman <jaltman@xxxxxxxxxxxx <mailto:jaltman@xxxxxxxxxxxx>>
    Link: https://lore.kernel.org/r/20240503150749.1001323-3-dhowells@xxxxxxxxxx
    Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/net/rxrpc/input.c b/net/rxrpc/input.c
index f7304e06aadca..5dfda1ac51dda 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)
 {
@@ -366,7 +377,7 @@ 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;
@@ -419,8 +430,6 @@ 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)) {
@@ -498,12 +507,16 @@ 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;
+		}
+	}
 }
 
 /*
@@ -514,9 +527,11 @@ 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)
@@ -536,7 +551,7 @@ 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;
@@ -549,7 +564,16 @@ 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);