perf: fix TestPerfReaderWakeupEvents

The WakeupEvents limit is per ring, one per CPU. And when we execute
BPF_PROG_RUN multiple times, we sometimes execute on different CPUs.
This means that samples don't all go into a single ring.

Fix this by forcing the producer to run on a single CPU.

Fixes #1419

Co-developed-by: Dylan Reimerink <dylan@isovalent.com>
Signed-off-by: Lorenz Bauer <lmb@isovalent.com>

internal/testutils/cpu.go

@@ -0,0 +1,32 @@
+package testutils
+
+import (
+	"runtime"
+	"testing"
+
+	"github.com/cilium/ebpf/internal/unix"
+
+	"github.com/go-quicktest/qt"
+)
+
+// LockOSThreadToSingleCPU force the current goroutine to run on a single CPU.
+func LockOSThreadToSingleCPU(tb testing.TB) {
+	tb.Helper()
+
+	runtime.LockOSThread()
+	tb.Cleanup(runtime.UnlockOSThread)
+
+	var old unix.CPUSet
+	err := unix.SchedGetaffinity(0, &old)
+	qt.Assert(tb, qt.IsNil(err))
+
+	// Schedule test to run on only CPU 0
+	var first unix.CPUSet
+	first.Set(0)
+	err = unix.SchedSetaffinity(0, &first)
+	qt.Assert(tb, qt.IsNil(err))
+
+	tb.Cleanup(func() {
+		_ = unix.SchedSetaffinity(0, &old)
+	})
+}

internal/unix/types_linux.go

@@ -100,6 +100,7 @@ type PerfEventMmapPage = linux.PerfEventMmapPage
 type EpollEvent = linux.EpollEvent
 type PerfEventAttr = linux.PerfEventAttr
 type Utsname = linux.Utsname
+type CPUSet = linux.CPUSet
 
 func Syscall(trap, a1, a2, a3 uintptr) (r1, r2 uintptr, err syscall.Errno) {
 	return linux.Syscall(trap, a1, a2, a3)
@@ -204,3 +205,11 @@ func Fstat(fd int, stat *Stat_t) error {
 func SetsockoptInt(fd, level, opt, value int) error {
 	return linux.SetsockoptInt(fd, level, opt, value)
 }
+
+func SchedSetaffinity(pid int, set *CPUSet) error {
+	return linux.SchedSetaffinity(pid, set)
+}
+
+func SchedGetaffinity(pid int, set *CPUSet) error {
+	return linux.SchedGetaffinity(pid, set)
+}

internal/unix/types_other.go

@@ -296,3 +296,15 @@ func Fstat(fd int, stat *Stat_t) error {
 func SetsockoptInt(fd, level, opt, value int) error {
 	return errNonLinux
 }
+
+type CPUSet struct{}
+
+func (*CPUSet) Set(int) {}
+
+func SchedSetaffinity(pid int, set *CPUSet) error {
+	return errNonLinux
+}
+
+func SchedGetaffinity(pid int, set *CPUSet) error {
+	return errNonLinux
+}

perf/reader_test.go

@@ -490,6 +490,8 @@ func TestPause(t *testing.T) {
 }
 
 func TestPerfReaderWakeupEvents(t *testing.T) {
+	testutils.LockOSThreadToSingleCPU(t)
+
 	events := perfEventArray(t)
 
 	numEvents := 2