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Date: Fri, 27 Jan 2023 17:03:39 -0500
From: Willem de Bruijn <willemb@...gle.com>
To: Andrei Gherzan <andrei.gherzan@...onical.com>
Cc: "David S. Miller" <davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>, Shuah Khan <shuah@...nel.org>,
netdev@...r.kernel.org, linux-kselftest@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH] selftests: net: udpgso_bench_tx: Introduce exponential
back-off retries
On Fri, Jan 27, 2023 at 1:16 PM Andrei Gherzan
<andrei.gherzan@...onical.com> wrote:
>
> 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@...onical.com>
Synchronizing the two processes is indeed tricky.
Perhaps more robust is opening an initial TCP connection, with
SO_RCVTIMEO to bound the waiting time. That covers all tests in one
go.
> ---
> 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++;
> }
send_tcp should not be affected, as connect will by then already have
succeeded. Also, as a reliable protocol it will internally retry,
after returning with success.
> @@ -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) {
should ideally only retry on the expected errno. Unreliable datagram
sendto will succeed and initially. It will fail with error later,
after reception of an ICMP dst unreachable response.
> + 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
>
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