[PATCH v2 3/3] tcp: Update data retransmission timeout

[Yumei Huang <yuhuang@redhat.com>]

Use an exponential backoff timeout with the initial timeout 1s
and total timeout 60s.

Signed-off-by: Yumei Huang <yuhuang@redhat.com>
---
 tcp.c | 25 +++++++++++++++++++------
 1 file changed, 19 insertions(+), 6 deletions(-)

diff --git a/tcp.c b/tcp.c
index 85bbdac..0db7f30 100644
--- a/tcp.c
+++ b/tcp.c
@@ -185,10 +185,15 @@
  *   for more than TCP_MAX_RETRIES or (tcp_syn_retries +
  *   tcp_syn_linear_timeouts) times in a row, reset the connection
  *
- * - ACK_TIMEOUT: if no ACK segment was received from tap/guest, after sending
- *   data (flag ACK_FROM_TAP_DUE with ESTABLISHED event), re-send data from the
- *   socket and reset sequence to what was acknowledged. If this persists for
- *   more than TCP_MAX_RETRIES times in a row, reset the connection
+ * - ACK_TIMEOUT_INIT: if no ACK segment was received from tap/guest, after
+ *   sending data (flag ACK_FROM_TAP_DUE with ESTABLISHED event), re-send data
+ *   from the socket and reset sequence to what was acknowledged. It's the
+ *   starting timeout for the first retransmission. If this persists for more
+ *   than TCP_MAX_RETRIES times in a row, reset the connection
+ *
+ * - ACK_TIMEOUT_TOTAL: if no ACK segment was received from tap/guest after
+ *   retransmitting data repeatedly from the socket within this time, reset
+ *   the connection
  *
  * - FIN_TIMEOUT: if a FIN segment was sent to tap/guest (flag ACK_FROM_TAP_DUE
  *   with TAP_FIN_SENT event), and no ACK is received within this time, reset
@@ -344,7 +349,8 @@ enum {
 
 #define ACK_INTERVAL			10		/* ms */
 #define SYN_TIMEOUT_INIT		1		/* s */
-#define ACK_TIMEOUT			2
+#define ACK_TIMEOUT_INIT		1
+#define ACK_TIMEOUT_TOTAL		60
 #define FIN_TIMEOUT			60
 #define ACT_TIMEOUT			7200
 
@@ -358,6 +364,9 @@ enum {
 	 ((conn)->events & (SOCK_FIN_RCVD | TAP_FIN_RCVD)))
 #define CONN_HAS(conn, set)	(((conn)->events & (set)) == (set))
 
+#define RETRY_ELAPSED(timeout_init, retries)		\
+	((timeout_init) * ((1 << ((retries) + 1)) - 2))
+
 /* Buffers to migrate pending data from send and receive queues. No, they don't
  * use memory if we don't use them. And we're going away after this, so splurge.
  */
@@ -596,7 +605,7 @@ static void tcp_timer_ctl(const struct ctx *c, struct tcp_tap_conn *conn)
 					(conn->retries - c->tcp.syn_linear_timeouts);
 		}
 		else
-			it.it_value.tv_sec = ACK_TIMEOUT;
+			it.it_value.tv_sec = ACK_TIMEOUT_INIT << conn->retries;
 	} else if (CONN_HAS(conn, SOCK_FIN_SENT | TAP_FIN_ACKED)) {
 		it.it_value.tv_sec = FIN_TIMEOUT;
 	} else {
@@ -2438,6 +2447,10 @@ void tcp_timer_handler(const struct ctx *c, union epoll_ref ref)
 		} else if (conn->retries == TCP_MAX_RETRIES) {
 			flow_dbg(conn, "retransmissions count exceeded");
 			tcp_rst(c, conn);
+		} else if(RETRY_ELAPSED(ACK_TIMEOUT_INIT, conn->retries) >=
+			ACK_TIMEOUT_TOTAL) {
+			flow_dbg(conn, "retransmissions timeout exceeded");
+			tcp_rst(c, conn);
 		} else {
 			flow_dbg(conn, "ACK timeout, retry");
 
-- 
2.47.0