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selftests: bpf: don't depend on hardcoded perf sample_freq

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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>
This commit is contained in:
Stanislav Fomichev 2019-03-19 14:53:24 -07:00 committed by Alexei Starovoitov
parent 0c4ea7f87a
commit b4b6aa8343
1 changed files with 15 additions and 1 deletions
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16
tools/testing/selftests/bpf/prog_tests/stacktrace_build_id_nmi.c
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@ -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))