perf_event__synthesize_event_update_unit
!perf_event__synthesize_event_update_unit(NULL, evsel, process_event_unit));
err = perf_event__synthesize_event_update_unit(tool, evsel, process);
int perf_event__synthesize_event_update_unit(const struct perf_tool *tool, struct evsel *evsel, perf_event__handler_t process);