diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index 7b4bb3229a16..ddf324e2e17a 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -1746,22 +1746,20 @@ static int perf_event_open(struct evsel *evsel,
 	return fd;
 }
 
-static int evsel__open_cpu(struct evsel *evsel, struct perf_cpu_map *cpus,
-		struct perf_thread_map *threads,
-		int start_cpu, int end_cpu)
+
+static struct perf_cpu_map *empty_cpu_map;
+static struct perf_thread_map *empty_thread_map;
+
+static int __evsel__prepare_open(struct evsel *evsel, struct perf_cpu_map *cpus,
+		struct perf_thread_map *threads)
 {
-	int cpu, thread, nthreads;
-	unsigned long flags = PERF_FLAG_FD_CLOEXEC;
-	int pid = -1, err, old_errno;
-	enum { NO_CHANGE, SET_TO_MAX, INCREASED_MAX } set_rlimit = NO_CHANGE;
+	int nthreads;
 
 	if ((perf_missing_features.write_backward && evsel->core.attr.write_backward) ||
 	    (perf_missing_features.aux_output     && evsel->core.attr.aux_output))
 		return -EINVAL;
 
 	if (cpus == NULL) {
-		static struct perf_cpu_map *empty_cpu_map;
-
 		if (empty_cpu_map == NULL) {
 			empty_cpu_map = perf_cpu_map__dummy_new();
 			if (empty_cpu_map == NULL)
@@ -1772,8 +1770,6 @@ static int evsel__open_cpu(struct evsel *evsel, struct perf_cpu_map *cpus,
 	}
 
 	if (threads == NULL) {
-		static struct perf_thread_map *empty_thread_map;
-
 		if (empty_thread_map == NULL) {
 			empty_thread_map = thread_map__new_by_tid(-1);
 			if (empty_thread_map == NULL)
@@ -1792,6 +1788,33 @@ static int evsel__open_cpu(struct evsel *evsel, struct perf_cpu_map *cpus,
 	    perf_evsel__alloc_fd(&evsel->core, cpus->nr, nthreads) < 0)
 		return -ENOMEM;
 
+	return 0;
+}
+
+static int evsel__open_cpu(struct evsel *evsel, struct perf_cpu_map *cpus,
+		struct perf_thread_map *threads,
+		int start_cpu, int end_cpu)
+{
+	int cpu, thread, nthreads;
+	unsigned long flags = PERF_FLAG_FD_CLOEXEC;
+	int pid = -1, err, old_errno;
+	enum { NO_CHANGE, SET_TO_MAX, INCREASED_MAX } set_rlimit = NO_CHANGE;
+
+	err = __evsel__prepare_open(evsel, cpus, threads);
+	if (err)
+		return err;
+
+	if (cpus == NULL)
+		cpus = empty_cpu_map;
+
+	if (threads == NULL)
+		threads = empty_thread_map;
+
+	if (evsel->core.system_wide)
+		nthreads = 1;
+	else
+		nthreads = threads->nr;
+
 	if (evsel->cgrp) {
 		flags |= PERF_FLAG_PID_CGROUP;
 		pid = evsel->cgrp->fd;