selftests: Add test for timing a bind request to a port with a populated bhash entry

This test populates the bhash table for a given port with
MAX_THREADS * MAX_CONNECTIONS sockets, and then times how long
a bind request on the port takes.

When populating the bhash table, we create the sockets and then bind
the sockets to the same address and port (SO_REUSEADDR and SO_REUSEPORT
are set). When timing how long a bind on the port takes, we bind on a
different address without SO_REUSEPORT set. We do not set SO_REUSEPORT
because we are interested in the case where the bind request does not
go through the tb->fastreuseport path, which is fragile (eg
tb->fastreuseport path does not work if binding with a different uid).

To run the test locally, I did:
* ulimit -n 65535000
* ip addr add 2001:0db8:0:f101::1 dev eth0
* ./bind_bhash_test 443
Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

tools/testing/selftests/net/.gitignore

@@ -36,3 +36,4 @@ gro
 ioam6_parser
 toeplitz
 cmsg_sender
+bind_bhash_test

tools/testing/selftests/net/Makefile

@@ -59,6 +59,7 @@ TEST_GEN_FILES += toeplitz
 TEST_GEN_FILES += cmsg_sender
 TEST_GEN_FILES += stress_reuseport_listen
 TEST_PROGS += test_vxlan_vnifiltering.sh
+TEST_GEN_FILES += bind_bhash_test
 
 TEST_FILES := settings
 
@@ -69,4 +70,5 @@ include bpf/Makefile
 
 $(OUTPUT)/reuseport_bpf_numa: LDLIBS += -lnuma
 $(OUTPUT)/tcp_mmap: LDLIBS += -lpthread
+$(OUTPUT)/bind_bhash_test: LDLIBS += -lpthread
 $(OUTPUT)/tcp_inq: LDLIBS += -lpthread

tools/testing/selftests/net/bind_bhash_test.c

+// SPDX-License-Identifier: GPL-2.0
+/*
+ * This times how long it takes to bind to a port when the port already
+ * has multiple sockets in its bhash table.
+ *
+ * In the setup(), we populate the port's bhash table with
+ * MAX_THREADS * MAX_CONNECTIONS number of entries.
+ */
+
+#include <unistd.h>
+#include <stdio.h>
+#include <netdb.h>
+#include <pthread.h>
+
+#define MAX_THREADS 600
+#define MAX_CONNECTIONS 40
+
+static const char *bind_addr = "::1";
+static const char *port;
+
+static int fd_array[MAX_THREADS][MAX_CONNECTIONS];
+
+static int bind_socket(int opt, const char *addr)
+{
+	struct addrinfo *res, hint = {};
+	int sock_fd, reuse = 1, err;
+
+	sock_fd = socket(AF_INET6, SOCK_STREAM, 0);
+	if (sock_fd < 0) {
+		perror("socket fd err");
+		return -1;
+	}
+
+	hint.ai_family = AF_INET6;
+	hint.ai_socktype = SOCK_STREAM;
+
+	err = getaddrinfo(addr, port, &hint, &res);
+	if (err) {
+		perror("getaddrinfo failed");
+		return -1;
+	}
+
+	if (opt) {
+		err = setsockopt(sock_fd, SOL_SOCKET, opt, &reuse, sizeof(reuse));
+		if (err) {
+			perror("setsockopt failed");
+			return -1;
+		}
+	}
+
+	err = bind(sock_fd, res->ai_addr, res->ai_addrlen);
+	if (err) {
+		perror("failed to bind to port");
+		return -1;
+	}
+
+	return sock_fd;
+}
+
+static void *setup(void *arg)
+{
+	int sock_fd, i;
+	int *array = (int *)arg;
+
+	for (i = 0; i < MAX_CONNECTIONS; i++) {
+		sock_fd = bind_socket(SO_REUSEADDR | SO_REUSEPORT, bind_addr);
+		if (sock_fd < 0)
+			return NULL;
+		array[i] = sock_fd;
+	}
+
+	return NULL;
+}
+
+int main(int argc, const char *argv[])
+{
+	int listener_fd, sock_fd, i, j;
+	pthread_t tid[MAX_THREADS];
+	clock_t begin, end;
+
+	if (argc != 2) {
+		printf("Usage: listener <port>\n");
+		return -1;
+	}
+
+	port = argv[1];
+
+	listener_fd = bind_socket(SO_REUSEADDR | SO_REUSEPORT, bind_addr);
+	if (listen(listener_fd, 100) < 0) {
+		perror("listen failed");
+		return -1;
+	}
+
+	/* Set up threads to populate the bhash table entry for the port */
+	for (i = 0; i < MAX_THREADS; i++)
+		pthread_create(&tid[i], NULL, setup, fd_array[i]);
+
+	for (i = 0; i < MAX_THREADS; i++)
+		pthread_join(tid[i], NULL);
+
+	begin = clock();
+
+	/* Bind to the same port on a different address */
+	sock_fd  = bind_socket(0, "2001:0db8:0:f101::1");
+
+	end = clock();
+
+	printf("time spent = %f\n", (double)(end - begin) / CLOCKS_PER_SEC);
+
+	/* clean up */
+	close(sock_fd);
+	close(listener_fd);
+	for (i = 0; i < MAX_THREADS; i++) {
+		for (j = 0; i < MAX_THREADS; i++)
+			close(fd_array[i][j]);
+	}
+
+	return 0;
+}