selftests/bpf: Add attach bench test

Adding test that reads all functions from ftrace available_filter_functions
file and attach them all through kprobe_multi API.

It also prints stats info with -v option, like on my setup:

test_bench_attach: found 48712 functions
test_bench_attach: attached in 1.069s
test_bench_attach: detached in 0.373s

Acked-by: Andrii Nakryiko <[e-mail]>
Signed-off-by: Jiri Olsa <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Alexei Starovoitov <[e-mail]>

tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c

···
 #include <test_progs.h>
 #include "kprobe_multi.skel.h"
 #include "trace_helpers.h"
+#include "kprobe_multi_empty.skel.h"
+#include "bpf/libbpf_internal.h"
+#include "bpf/hashmap.h"
 
 static void kprobe_multi_test_run(struct kprobe_multi *skel, bool test_return)
 {
···
 	kprobe_multi__destroy(skel);
 }
 
+static inline __u64 get_time_ns(void)
+{
+	struct timespec t;
+
+	clock_gettime(CLOCK_MONOTONIC, &t);
+	return (__u64) t.tv_sec * 1000000000 + t.tv_nsec;
+}
+
+static size_t symbol_hash(const void *key, void *ctx __maybe_unused)
+{
+	return str_hash((const char *) key);
+}
+
+static bool symbol_equal(const void *key1, const void *key2, void *ctx __maybe_unused)
+{
+	return strcmp((const char *) key1, (const char *) key2) == 0;
+}
+
+static int get_syms(char ***symsp, size_t *cntp)
+{
+	size_t cap = 0, cnt = 0, i;
+	char *name, **syms = NULL;
+	struct hashmap *map;
+	char buf[256];
+	FILE *f;
+	int err;
+
+	/*
+	 * The available_filter_functions contains many duplicates,
+	 * but other than that all symbols are usable in kprobe multi
+	 * interface.
+	 * Filtering out duplicates by using hashmap__add, which won't
+	 * add existing entry.
+	 */
+	f = fopen("/sys/kernel/debug/tracing/available_filter_functions", "r");
+	if (!f)
+		return -EINVAL;
+
+	map = hashmap__new(symbol_hash, symbol_equal, NULL);
+	if (IS_ERR(map))
+		goto error;
+
+	while (fgets(buf, sizeof(buf), f)) {
+		/* skip modules */
+		if (strchr(buf, '['))
+			continue;
+		if (sscanf(buf, "%ms$*[^\n]\n", &name) != 1)
+			continue;
+		/*
+		 * We attach to almost all kernel functions and some of them
+		 * will cause 'suspicious RCU usage' when fprobe is attached
+		 * to them. Filter out the current culprits - arch_cpu_idle
+		 * and rcu_* functions.
+		 */
+		if (!strcmp(name, "arch_cpu_idle"))
+			continue;
+		if (!strncmp(name, "rcu_", 4))
+			continue;
+		err = hashmap__add(map, name, NULL);
+		if (err) {
+			free(name);
+			if (err == -EEXIST)
+				continue;
+			goto error;
+		}
+		err = libbpf_ensure_mem((void **) &syms, &cap,
+					sizeof(*syms), cnt + 1);
+		if (err) {
+			free(name);
+			goto error;
+		}
+		syms[cnt] = name;
+		cnt++;
+	}
+
+	*symsp = syms;
+	*cntp = cnt;
+
+error:
+	fclose(f);
+	hashmap__free(map);
+	if (err) {
+		for (i = 0; i < cnt; i++)
+			free(syms[cnt]);
+		free(syms);
+	}
+	return err;
+}
+
+static void test_bench_attach(void)
+{
+	LIBBPF_OPTS(bpf_kprobe_multi_opts, opts);
+	struct kprobe_multi_empty *skel = NULL;
+	long attach_start_ns, attach_end_ns;
+	long detach_start_ns, detach_end_ns;
+	double attach_delta, detach_delta;
+	struct bpf_link *link = NULL;
+	char **syms = NULL;
+	size_t cnt, i;
+
+	if (!ASSERT_OK(get_syms(&syms, &cnt), "get_syms"))
+		return;
+
+	skel = kprobe_multi_empty__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "kprobe_multi_empty__open_and_load"))
+		goto cleanup;
+
+	opts.syms = (const char **) syms;
+	opts.cnt = cnt;
+
+	attach_start_ns = get_time_ns();
+	link = bpf_program__attach_kprobe_multi_opts(skel->progs.test_kprobe_empty,
+						     NULL, &opts);
+	attach_end_ns = get_time_ns();
+
+	if (!ASSERT_OK_PTR(link, "bpf_program__attach_kprobe_multi_opts"))
+		goto cleanup;
+
+	detach_start_ns = get_time_ns();
+	bpf_link__destroy(link);
+	detach_end_ns = get_time_ns();
+
+	attach_delta = (attach_end_ns - attach_start_ns) / 1000000000.0;
+	detach_delta = (detach_end_ns - detach_start_ns) / 1000000000.0;
+
+	printf("%s: found %lu functions\n", __func__, cnt);
+	printf("%s: attached in %7.3lfs\n", __func__, attach_delta);
+	printf("%s: detached in %7.3lfs\n", __func__, detach_delta);
+
+cleanup:
+	kprobe_multi_empty__destroy(skel);
+	if (syms) {
+		for (i = 0; i < cnt; i++)
+			free(syms[i]);
+		free(syms);
+	}
+}
+
 void test_kprobe_multi_test(void)
 {
 	if (!ASSERT_OK(load_kallsyms(), "load_kallsyms"))
···
 		test_attach_api_syms();
 	if (test__start_subtest("attach_api_fails"))
 		test_attach_api_fails();
+	if (test__start_subtest("bench_attach"))
+		test_bench_attach();
 }

tools/testing/selftests/bpf/progs/kprobe_multi_empty.c

···
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+char _license[] SEC("license") = "GPL";
+
+SEC("kprobe.multi/")
+int test_kprobe_empty(struct pt_regs *ctx)
+{
+	return 0;
+}