From:   Andrei Gherzan <andrei.gherzan@canonical.com>
To:     "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>, Shuah Khan <shuah@kernel.org>,
        Willem de Bruijn <willemb@google.com>
Cc:     Andrei Gherzan <andrei.gherzan@canonical.com>,
        netdev@vger.kernel.org, linux-kselftest@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: [PATCH] selftests: net: udpgso_bench_tx: Introduce exponential back-off retries
Date:   Fri, 27 Jan 2023 18:16:25 +0000
Message-Id: <20230127181625.286546-1-andrei.gherzan@canonical.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

The tx and rx test programs are used in a couple of test scripts including
"udpgro_bench.sh". Taking this as an example, when the rx/tx programs
are invoked subsequently, there is a chance that the rx one is not ready to
accept socket connections. This racing bug could fail the test with at
least one of the following:

./udpgso_bench_tx: connect: Connection refused
./udpgso_bench_tx: sendmsg: Connection refused
./udpgso_bench_tx: write: Connection refused

This change addresses this by adding routines that retry the socket
operations with an exponential back off algorithm from 100ms to 2s.

Fixes: 3a687bef148d ("selftests: udp gso benchmark")
Signed-off-by: Andrei Gherzan <andrei.gherzan@canonical.com>
---
 tools/testing/selftests/net/udpgso_bench_tx.c | 57 +++++++++++++------
 1 file changed, 41 insertions(+), 16 deletions(-)

diff --git a/tools/testing/selftests/net/udpgso_bench_tx.c b/tools/testing/selftests/net/udpgso_bench_tx.c
index f1fdaa270291..4dea9ee7eb46 100644
--- a/tools/testing/selftests/net/udpgso_bench_tx.c
+++ b/tools/testing/selftests/net/udpgso_bench_tx.c
@@ -53,6 +53,9 @@
 
 #define NUM_PKT		100
 
+#define MAX_DELAY	2000000
+#define INIT_DELAY	100000
+
 static bool	cfg_cache_trash;
 static int	cfg_cpu		= -1;
 static int	cfg_connected	= true;
@@ -257,13 +260,18 @@ static void flush_errqueue(int fd, const bool do_poll)
 static int send_tcp(int fd, char *data)
 {
 	int ret, done = 0, count = 0;
+	useconds_t delay = INIT_DELAY;
 
 	while (done < cfg_payload_len) {
-		ret = send(fd, data + done, cfg_payload_len - done,
-			   cfg_zerocopy ? MSG_ZEROCOPY : 0);
-		if (ret == -1)
-			error(1, errno, "write");
-
+		delay = INIT_DELAY;
+		while ((ret = send(fd, data + done, cfg_payload_len - done,
+				cfg_zerocopy ? MSG_ZEROCOPY : 0)) == -1) {
+			usleep(delay);
+			if (delay < MAX_DELAY)
+				delay *= 2;
+			else
+				error(1, errno, "write");
+		}
 		done += ret;
 		count++;
 	}
@@ -274,17 +282,23 @@ static int send_tcp(int fd, char *data)
 static int send_udp(int fd, char *data)
 {
 	int ret, total_len, len, count = 0;
+	useconds_t delay = INIT_DELAY;
 
 	total_len = cfg_payload_len;
 
 	while (total_len) {
 		len = total_len < cfg_mss ? total_len : cfg_mss;
 
-		ret = sendto(fd, data, len, cfg_zerocopy ? MSG_ZEROCOPY : 0,
-			     cfg_connected ? NULL : (void *)&cfg_dst_addr,
-			     cfg_connected ? 0 : cfg_alen);
-		if (ret == -1)
-			error(1, errno, "write");
+		delay = INIT_DELAY;
+		while ((ret = sendto(fd, data, len, cfg_zerocopy ? MSG_ZEROCOPY : 0,
+				cfg_connected ? NULL : (void *)&cfg_dst_addr,
+				cfg_connected ? 0 : cfg_alen)) == -1) {
+			usleep(delay);
+			if (delay < MAX_DELAY)
+				delay *= 2;
+			else
+				error(1, errno, "write");
+		}
 		if (ret != len)
 			error(1, errno, "write: %uB != %uB\n", ret, len);
 
@@ -378,6 +392,7 @@ static int send_udp_segment(int fd, char *data)
 	struct iovec iov = {0};
 	size_t msg_controllen;
 	struct cmsghdr *cmsg;
+	useconds_t delay = INIT_DELAY;
 	int ret;
 
 	iov.iov_base = data;
@@ -401,9 +416,13 @@ static int send_udp_segment(int fd, char *data)
 	msg.msg_name = (void *)&cfg_dst_addr;
 	msg.msg_namelen = cfg_alen;
 
-	ret = sendmsg(fd, &msg, cfg_zerocopy ? MSG_ZEROCOPY : 0);
-	if (ret == -1)
-		error(1, errno, "sendmsg");
+	while ((ret = sendmsg(fd, &msg, cfg_zerocopy ? MSG_ZEROCOPY : 0)) == -1) {
+		usleep(delay);
+		if (delay < MAX_DELAY)
+			delay *= 2;
+		else
+			error(1, errno, "sendmsg");
+	}
 	if (ret != iov.iov_len)
 		error(1, 0, "sendmsg: %u != %llu\n", ret,
 			(unsigned long long)iov.iov_len);
@@ -616,6 +635,7 @@ int main(int argc, char **argv)
 {
 	unsigned long num_msgs, num_sends;
 	unsigned long tnow, treport, tstop;
+	useconds_t delay = INIT_DELAY;
 	int fd, i, val, ret;
 
 	parse_opts(argc, argv);
@@ -648,9 +668,14 @@ int main(int argc, char **argv)
 		}
 	}
 
-	if (cfg_connected &&
-	    connect(fd, (void *)&cfg_dst_addr, cfg_alen))
-		error(1, errno, "connect");
+	if (cfg_connected)
+		while (connect(fd, (void *)&cfg_dst_addr, cfg_alen)) {
+			usleep(delay);
+			if (delay < MAX_DELAY)
+				delay *= 2;
+			else
+				error(1, errno, "connect");
+		}
 
 	if (cfg_segment)
 		set_pmtu_discover(fd, cfg_family == PF_INET);
-- 
2.34.1