perf_event_groups_first
for (event = perf_event_groups_first(groups, cpu, pmu, NULL); \
__heap_add(&event_heap, perf_event_groups_first(groups, -1, pmu, NULL));
__heap_add(&event_heap, perf_event_groups_first(groups, cpu, pmu, NULL));
__heap_add(&event_heap, perf_event_groups_first(groups, cpu, pmu, css->cgroup));