[PATCH 8/8] tcp_splice: Exit forwarding earlier when stalled read side

[David Gibson <david@gibson.dropbear.id.au>]

At the end of our loop we have a conditional 'break' that exits if we're
at EOF on the read side and have nothing left in the pipe.  This doesn't
depend on anything write-side, so we can move it earlier, avoiding an
unnecessary write side splice in this case.

Furthermore, there's also nothing to be done write side if we've hit EAGAIN
on the read side and the pipe is empty, so exit early for that case as
well.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
---
 tcp_splice.c | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/tcp_splice.c b/tcp_splice.c
index 565596d3..623ca926 100644
--- a/tcp_splice.c
+++ b/tcp_splice.c
@@ -497,9 +497,17 @@ static int tcp_splice_forward(struct ctx *c,
 
 		flow_trace(conn, "%zi from read-side call", readlen);
 
-		if (!readlen) {
-			conn_event(conn, FIN_RCVD(fromsidei));
-		} else if (readlen > 0) {
+		if (readlen <= 0) {
+			if (!readlen) /* EOF */
+				conn_event(conn, FIN_RCVD(fromsidei));
+
+			/* We're either blocked or at EOF on the read side, and
+			 * there's nothing in the pipe so there's nothing to do
+			 * write side either.
+			 */
+			if (!conn->pending[fromsidei])
+				break;
+		} else {
 			conn->pending[fromsidei] += readlen;
 
 			if (readlen >= (long)c->tcp.pipe_size * 90 / 100)
@@ -530,10 +538,6 @@ static int tcp_splice_forward(struct ctx *c,
 			break;
 
 		conn->pending[fromsidei] -= written;
-
-		if (conn->events & FIN_RCVD(fromsidei) &&
-		    !conn->pending[fromsidei])
-			break;
 	}
 
 	/* We need write-side wakeups if and only if we have data in the pipe to
-- 
2.54.0