selftests: bpf: don't depend on hardcoded perf sample_freq (b4b6aa83) · Commits · 戴 / test

When running stacktrace_build_id_nmi, try to query kernel.perf_event_max_sample_rate sysctl and use it as a sample_freq. If there was an error reading sysctl, fallback to 5000. kernel.perf_event_max_sample_rate sysctl can drift and/or can be adjusted by the perf tool, so assuming a fixed number might be problematic on a long running machine. Signed-off-by:

Stanislav Fomichev <sdf@google.com> Signed-off-by:

Alexei Starovoitov <ast@kernel.org>

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

+15 −1

Original line number	Diff line number	Diff line
		// SPDX-License-Identifier: GPL-2.0
		#include <test_progs.h>

		static __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)
		return sample_freq;
		fscanf(f, "%llu", &sample_freq);
		fclose(f);
		return sample_freq;
		}

		void test_stacktrace_build_id_nmi(void)
		{
		int control_map_fd, stackid_hmap_fd, stackmap_fd, stack_amap_fd;
		const char *file = "./test_stacktrace_build_id.o";
		int err, pmu_fd, prog_fd;
		struct perf_event_attr attr = {
		.sample_freq = 5000,
		.freq = 1,
		.type = PERF_TYPE_HARDWARE,
		.config = PERF_COUNT_HW_CPU_CYCLES,
		@@ -20,6 +32,8 @@ void test_stacktrace_build_id_nmi(void)
		int build_id_matches = 0;
		int retry = 1;

		attr.sample_freq = read_perf_max_sample_freq();

		retry:
		err = bpf_prog_load(file, BPF_PROG_TYPE_PERF_EVENT, &obj, &prog_fd);
		if (CHECK(err, "prog_load", "err %d errno %d\n", err, errno))

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