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selftests/bpf: Avoid spurious failures perf_link

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perf_link creates a system-wide perf event pinned to CPU 0 (pid=-1, cpu=0)
and also pins the test thread to CPU 0. Under concurrent selftests this
can lead to cross-test interference and CPU 0 contention, making the test
flaky.

Create a per-task perf event instead (pid=0, cpu=-1) and drop CPU pinning
from burn_cpu(). Use barrier() to prevent the burn loop from being
optimized away. Drop the serial_ prefix so the test can run in parallel.
Also remove the stale TODO comment.

Tested:
  ./test_progs -t perf_link -vv
  ./test_progs -j$(nproc) -t perf_link -vv
  for i in $(seq 1 50); do ./test_progs -j$(nproc) -t perf_link; done

Signed-off-by: Sun Jian <sun.jian.kdev@gmail.com>
Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20260305084306.283983-1-sun.jian.kdev@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Sun Jian 2026-03-05 16:43:05 +08:00 committed by Alexei Starovoitov
parent 77378dabb5
commit 888329ba6c
1 changed files with 5 additions and 15 deletions
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20
tools/testing/selftests/bpf/prog_tests/perf_link.c
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@ -1,8 +1,7 @@
// SPDX-License-Identifier: GPL-2.0
/* Copyright (c) 2021 Facebook */
#define _GNU_SOURCE
#include <pthread.h>
#include <sched.h>
#include <linux/compiler.h>
#include <test_progs.h>
#include "testing_helpers.h"
#include "test_perf_link.skel.h"
@ -12,23 +11,14 @@
static void burn_cpu(void)
{
volatile int j = 0;
cpu_set_t cpu_set;
int i, err;
/* generate some branches on cpu 0 */
CPU_ZERO(&cpu_set);
CPU_SET(0, &cpu_set);
err = pthread_setaffinity_np(pthread_self(), sizeof(cpu_set), &cpu_set);
ASSERT_OK(err, "set_thread_affinity");
int i;
/* spin the loop for a while (random high number) */
for (i = 0; i < 1000000; ++i)
++j;
barrier();
}
/* TODO: often fails in concurrent mode */
void serial_test_perf_link(void)
void test_perf_link(void)
{
struct test_perf_link *skel = NULL;
struct perf_event_attr attr;
@ -45,7 +35,7 @@ void serial_test_perf_link(void)
attr.config = PERF_COUNT_SW_CPU_CLOCK;
attr.freq = 1;
attr.sample_freq = 1000;
pfd = syscall(__NR_perf_event_open, &attr, -1, 0, -1, PERF_FLAG_FD_CLOEXEC);
pfd = syscall(__NR_perf_event_open, &attr, 0, -1, -1, PERF_FLAG_FD_CLOEXEC);
if (!ASSERT_GE(pfd, 0, "perf_fd"))
goto cleanup;