samples/bpf: replace broken overhead microbenchmark with fib_table_lookup

The test_overhead bpf program is designed to compare performance
between tracepoint and kprobe. Initially it used task_rename and
urandom_read tracepoint.

However, commit 14c174633f ("random: remove unused tracepoints")
removed urandom_read tracepoint, and for this reason the test_overhead
got broken.

This commit introduces new microbenchmark using fib_table_lookup.
This microbenchmark sends UDP packets to localhost in order to invoke
fib_table_lookup.

In a nutshell:
fd = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
addr.sin_addr.s_addr = inet_addr(DUMMY_IP);
addr.sin_port = htons(DUMMY_PORT);
for() {
    sendto(fd, buf, strlen(buf), 0,
            (struct sockaddr *)&addr, sizeof(addr));
}

on 4 cpus in parallel:
                                            lookup per sec
base (no tracepoints, no kprobes)               381k
with kprobe at fib_table_lookup()               325k
with tracepoint at fib:fib_table_lookup         330k
with raw_tracepoint at fib:fib_table_lookup     365k

Fixes: 14c174633f ("random: remove unused tracepoints")

Signed-off-by: Daniel T. Lee <danieltimlee@gmail.com>
Link: https://lore.kernel.org/r/20230115071613.125791-6-danieltimlee@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

samples/bpf/test_overhead_kprobe_kern.c

@@ -39,7 +39,7 @@ int prog(struct pt_regs *ctx)
 	return 0;
 }
 
-SEC("kprobe/urandom_read")
+SEC("kprobe/fib_table_lookup")
 int prog2(struct pt_regs *ctx)
 {
 	return 0;

samples/bpf/test_overhead_raw_tp_kern.c

@@ -9,7 +9,7 @@ int prog(struct bpf_raw_tracepoint_args *ctx)
 	return 0;
 }
 
-SEC("raw_tracepoint/urandom_read")
+SEC("raw_tracepoint/fib_table_lookup")
 int prog2(struct bpf_raw_tracepoint_args *ctx)
 {
 	return 0;

samples/bpf/test_overhead_tp_kern.c

@@ -22,15 +22,27 @@ int prog(struct task_rename *ctx)
 	return 0;
 }
 
-/* from /sys/kernel/debug/tracing/events/random/urandom_read/format */
-struct urandom_read {
+/* from /sys/kernel/debug/tracing/events/fib/fib_table_lookup/format */
+struct fib_table_lookup {
 	__u64 pad;
-	int got_bits;
-	int pool_left;
-	int input_left;
+	__u32 tb_id;
+	int err;
+	int oif;
+	int iif;
+	__u8 proto;
+	__u8 tos;
+	__u8 scope;
+	__u8 flags;
+	__u8 src[4];
+	__u8 dst[4];
+	__u8 gw4[4];
+	__u8 gw6[16];
+	__u16 sport;
+	__u16 dport;
+	char name[16];
 };
-SEC("tracepoint/random/urandom_read")
-int prog2(struct urandom_read *ctx)
+SEC("tracepoint/fib/fib_table_lookup")
+int prog2(struct fib_table_lookup *ctx)
 {
 	return 0;
 }

samples/bpf/test_overhead_user.c

@@ -11,6 +11,8 @@
 #include <unistd.h>
 #include <assert.h>
 #include <sys/wait.h>
+#include <sys/socket.h>
+#include <arpa/inet.h>
 #include <stdlib.h>
 #include <signal.h>
 #include <linux/bpf.h>
@@ -20,6 +22,8 @@
 #include <bpf/libbpf.h>
 
 #define MAX_CNT 1000000
+#define DUMMY_IP "127.0.0.1"
+#define DUMMY_PORT 80
 
 static struct bpf_link *links[2];
 static struct bpf_object *obj;
@@ -35,8 +39,8 @@ static __u64 time_get_ns(void)
 
 static void test_task_rename(int cpu)
 {
-	__u64 start_time;
 	char buf[] = "test\n";
+	__u64 start_time;
 	int i, fd;
 
 	fd = open("/proc/self/comm", O_WRONLY|O_TRUNC);
@@ -57,26 +61,32 @@ static void test_task_rename(int cpu)
 	close(fd);
 }
 
-static void test_urandom_read(int cpu)
+static void test_fib_table_lookup(int cpu)
 {
+	struct sockaddr_in addr;
+	char buf[] = "test\n";
 	__u64 start_time;
-	char buf[4];
 	int i, fd;
 
-	fd = open("/dev/urandom", O_RDONLY);
+	fd = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
 	if (fd < 0) {
-		printf("couldn't open /dev/urandom\n");
+		printf("couldn't open socket\n");
 		exit(1);
 	}
+	memset((char *)&addr, 0, sizeof(addr));
+	addr.sin_addr.s_addr = inet_addr(DUMMY_IP);
+	addr.sin_port = htons(DUMMY_PORT);
+	addr.sin_family = AF_INET;
 	start_time = time_get_ns();
 	for (i = 0; i < MAX_CNT; i++) {
-		if (read(fd, buf, sizeof(buf)) < 0) {
-			printf("failed to read from /dev/urandom: %s\n", strerror(errno));
+		if (sendto(fd, buf, strlen(buf), 0,
+			   (struct sockaddr *)&addr, sizeof(addr)) < 0) {
+			printf("failed to start ping: %s\n", strerror(errno));
 			close(fd);
 			return;
 		}
 	}
-	printf("urandom_read:%d: %lld events per sec\n",
+	printf("fib_table_lookup:%d: %lld events per sec\n",
 	       cpu, MAX_CNT * 1000000000ll / (time_get_ns() - start_time));
 	close(fd);
 }
@@ -92,7 +102,7 @@ static void loop(int cpu, int flags)
 	if (flags & 1)
 		test_task_rename(cpu);
 	if (flags & 2)
-		test_urandom_read(cpu);
+		test_fib_table_lookup(cpu);
 }
 
 static void run_perf_test(int tasks, int flags)