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@xxxxxxxxxx>
---
.../bpf/prog_tests/stacktrace_build_id_nmi.c | 16 +++++++++++++++-
1 file changed, 15 insertions(+), 1 deletion(-)
diff --git a/tools/testing/selftests/bpf/prog_tests/stacktrace_build_id_nmi.c b/tools/testing/selftests/bpf/prog_tests/stacktrace_build_id_nmi.c
index 8a114bb1c379..1c1a2f75f3d8 100644
--- a/tools/testing/selftests/bpf/prog_tests/stacktrace_build_id_nmi.c
+++ b/tools/testing/selftests/bpf/prog_tests/stacktrace_build_id_nmi.c
@@ -1,13 +1,25 @@
// 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))
--
2.21.0.225.g810b269d1ac-goog
