selftests/bpf: Use read_perf_max_sample_freq() in perf_event_stackmap

Currently, perf_event sample period in perf_event_stackmap is set too low
that the test fails randomly. Fix this by using the max sample frequency,
from read_perf_max_sample_freq().

Move read_perf_max_sample_freq() to testing_helpers.c. Replace the CHECK()
with if-printf, as CHECK is not available in testing_helpers.c.

Fixes: 1da4864c ("selftests/bpf: Add callchain_stackid")
Signed-off-by: Song Liu <song@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20230412210423.900851-2-song@kernel.org

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

@@ -63,7 +63,8 @@ void test_perf_event_stackmap(void)
 			PERF_SAMPLE_BRANCH_NO_FLAGS |
 			PERF_SAMPLE_BRANCH_NO_CYCLES |
 			PERF_SAMPLE_BRANCH_CALL_STACK,
-		.sample_period = 5000,
+		.freq = 1,
+		.sample_freq = read_perf_max_sample_freq(),
 		.size = sizeof(struct perf_event_attr),
 	};
 	struct perf_event_stackmap *skel;

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

@@ -2,21 +2,6 @@
 #include <test_progs.h>
 #include "test_stacktrace_build_id.skel.h"
 
-static __u64 read_perf_max_sample_freq(void)
-{
-	__u64 sample_freq = 5000; /* fallback to 5000 on error */
-	FILE *f;
-	__u32 duration = 0;
-
-	f = fopen("/proc/sys/kernel/perf_event_max_sample_rate", "r");
-	if (f == NULL)
-		return sample_freq;
-	CHECK(fscanf(f, "%llu", &sample_freq) != 1, "Get max sample rate",
-		  "return default value: 5000,err %d\n", -errno);
-	fclose(f);
-	return sample_freq;
-}
-
 void test_stacktrace_build_id_nmi(void)
 {
 	int control_map_fd, stackid_hmap_fd, stackmap_fd;

tools/testing/selftests/bpf/testing_helpers.c

@@ -229,3 +229,23 @@ int bpf_test_load_program(enum bpf_prog_type type, const struct bpf_insn *insns,
 
 	return bpf_prog_load(type, NULL, license, insns, insns_cnt, &opts);
 }
+
+__u64 read_perf_max_sample_freq(void)
+{
+	__u64 sample_freq = 5000; /* fallback to 5000 on error */
+	FILE *f;
+
+	f = fopen("/proc/sys/kernel/perf_event_max_sample_rate", "r");
+	if (f == NULL) {
+		printf("Failed to open /proc/sys/kernel/perf_event_max_sample_rate: err %d\n"
+		       "return default value: 5000\n", -errno);
+		return sample_freq;
+	}
+	if (fscanf(f, "%llu", &sample_freq) != 1) {
+		printf("Failed to parse /proc/sys/kernel/perf_event_max_sample_rate: err %d\n"
+		       "return default value: 5000\n", -errno);
+	}
+
+	fclose(f);
+	return sample_freq;
+}

tools/testing/selftests/bpf/testing_helpers.h

@@ -20,3 +20,5 @@ struct test_filter_set;
 int parse_test_list(const char *s,
 		    struct test_filter_set *test_set,
 		    bool is_glob_pattern);
+
+__u64 read_perf_max_sample_freq(void);