[PATCH net-next v2 20/21] rxrpc: Clean up the resend algorithm

[David Howells]

Clean up the DATA packet resending algorithm to retransmit packets as we
come across them whilst walking the transmission buffer rather than queuing
them for retransmission at the end.  This can be done as ACK parsing - and
thus the discarding of successful packets - is now done in the same thread
rather than separately in softirq context and a locked section is no longer
required.

Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
cc: Marc Dionne <marc.dionne@xxxxxxxxxxxx>
cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
cc: Eric Dumazet <edumazet@xxxxxxxxxx>
cc: Jakub Kicinski <kuba@xxxxxxxxxx>
cc: Paolo Abeni <pabeni@xxxxxxxxxx>
cc: linux-afs@xxxxxxxxxxxxxxxxxxx
cc: netdev@xxxxxxxxxxxxxxx
---
 net/rxrpc/call_event.c | 79 ++++++++++++++++++++----------------------
 1 file changed, 38 insertions(+), 41 deletions(-)

diff --git a/net/rxrpc/call_event.c b/net/rxrpc/call_event.c
index 2a9f74eb7c46..6c5e3054209b 100644
--- a/net/rxrpc/call_event.c
+++ b/net/rxrpc/call_event.c
@@ -71,23 +71,18 @@ void rxrpc_resend(struct rxrpc_call *call, struct sk_buff *ack_skb)
 	struct rxrpc_skb_priv *sp;
 	struct rxrpc_txbuf *txb;
 	rxrpc_seq_t transmitted = call->tx_transmitted;
-	ktime_t now, max_age, oldest, ack_ts, delay;
-	bool unacked = false;
+	ktime_t next_resend = KTIME_MAX, rto = ns_to_ktime(call->peer->rto_us * NSEC_PER_USEC);
+	ktime_t resend_at = KTIME_MAX, now, delay;
+	bool unacked = false, did_send = false;
 	unsigned int i;
-	LIST_HEAD(retrans_queue);
 
 	_enter("{%d,%d}", call->acks_hard_ack, call->tx_top);
 
 	now = ktime_get_real();
-	max_age = ktime_sub_us(now, call->peer->rto_us);
-	oldest = now;
 
 	if (list_empty(&call->tx_buffer))
 		goto no_resend;
 
-	if (list_empty(&call->tx_buffer))
-		goto no_further_resend;
-
 	trace_rxrpc_resend(call, ack_skb);
 	txb = list_first_entry(&call->tx_buffer, struct rxrpc_txbuf, call_link);
 
@@ -115,19 +110,23 @@ void rxrpc_resend(struct rxrpc_call *call, struct sk_buff *ack_skb)
 			goto no_further_resend;
 
 		found_txb:
-			if (after(txb->serial, call->acks_highest_serial))
+			resend_at = ktime_add(txb->last_sent, rto);
+			if (after(txb->serial, call->acks_highest_serial)) {
+				if (ktime_after(resend_at, now) &&
+				    ktime_before(resend_at, next_resend))
+					next_resend = resend_at;
 				continue; /* Ack point not yet reached */
+			}
 
 			rxrpc_see_txbuf(txb, rxrpc_txbuf_see_unacked);
 
-			if (list_empty(&txb->tx_link)) {
-				list_add_tail(&txb->tx_link, &retrans_queue);
-				txb->flags |= RXRPC_TXBUF_RESENT;
-			}
-
 			trace_rxrpc_retransmit(call, txb->seq, txb->serial,
-					       ktime_to_ns(ktime_sub(txb->last_sent,
-								     max_age)));
+					       ktime_sub(resend_at, now));
+
+			txb->flags |= RXRPC_TXBUF_RESENT;
+			rxrpc_transmit_one(call, txb);
+			did_send = true;
+			now = ktime_get_real();
 
 			if (list_is_last(&txb->call_link, &call->tx_buffer))
 				goto no_further_resend;
@@ -144,6 +143,8 @@ void rxrpc_resend(struct rxrpc_call *call, struct sk_buff *ack_skb)
 		goto no_further_resend;
 
 	list_for_each_entry_from(txb, &call->tx_buffer, call_link) {
+		resend_at = ktime_add(txb->last_sent, rto);
+
 		if (before_eq(txb->seq, call->acks_prev_seq))
 			continue;
 		if (after(txb->seq, call->tx_transmitted))
@@ -153,25 +154,30 @@ void rxrpc_resend(struct rxrpc_call *call, struct sk_buff *ack_skb)
 		    before(txb->serial, ntohl(ack->serial)))
 			goto do_resend; /* Wasn't accounted for by a more recent ping. */
 
-		if (ktime_after(txb->last_sent, max_age)) {
-			if (ktime_before(txb->last_sent, oldest))
-				oldest = txb->last_sent;
+		if (ktime_after(resend_at, now)) {
+			if (ktime_before(resend_at, next_resend))
+				next_resend = resend_at;
 			continue;
 		}
 
 	do_resend:
 		unacked = true;
-		if (list_empty(&txb->tx_link)) {
-			list_add_tail(&txb->tx_link, &retrans_queue);
-			txb->flags |= RXRPC_TXBUF_RESENT;
-			rxrpc_inc_stat(call->rxnet, stat_tx_data_retrans);
-		}
+
+		txb->flags |= RXRPC_TXBUF_RESENT;
+		rxrpc_transmit_one(call, txb);
+		did_send = true;
+		rxrpc_inc_stat(call->rxnet, stat_tx_data_retrans);
+		now = ktime_get_real();
 	}
 
 no_further_resend:
 no_resend:
-	delay = rxrpc_get_rto_backoff(call->peer, !list_empty(&retrans_queue));
-	call->resend_at = ktime_add(oldest, delay);
+	if (resend_at < KTIME_MAX) {
+		delay = rxrpc_get_rto_backoff(call->peer, did_send);
+		resend_at = ktime_add(resend_at, delay);
+		trace_rxrpc_timer_set(call, resend_at - now, rxrpc_timer_trace_resend_reset);
+	}
+	call->resend_at = resend_at;
 
 	if (unacked)
 		rxrpc_congestion_timeout(call);
@@ -180,24 +186,15 @@ void rxrpc_resend(struct rxrpc_call *call, struct sk_buff *ack_skb)
 	 * that an ACK got lost somewhere.  Send a ping to find out instead of
 	 * retransmitting data.
 	 */
-	if (list_empty(&retrans_queue)) {
-		trace_rxrpc_timer_set(call, delay, rxrpc_timer_trace_resend_reset);
-		ack_ts = ktime_sub(now, call->acks_latest_ts);
-		if (ktime_to_us(ack_ts) < (call->peer->srtt_us >> 3))
-			goto out;
-		rxrpc_send_ACK(call, RXRPC_ACK_PING, 0,
-			       rxrpc_propose_ack_ping_for_0_retrans);
-		goto out;
-	}
+	if (!did_send) {
+		ktime_t next_ping = ktime_add_us(call->acks_latest_ts,
+						 call->peer->srtt_us >> 3);
 
-	/* Retransmit the queue */
-	while ((txb = list_first_entry_or_null(&retrans_queue,
-					       struct rxrpc_txbuf, tx_link))) {
-		list_del_init(&txb->tx_link);
-		rxrpc_transmit_one(call, txb);
+		if (ktime_sub(next_ping, now) <= 0)
+			rxrpc_send_ACK(call, RXRPC_ACK_PING, 0,
+				       rxrpc_propose_ack_ping_for_0_retrans);
 	}
 
-out:
 	_leave("");
 }