perf intel-pt: Track sideband system-wide when needed

User space tasks can migrate between CPUs, so when tracing selected CPUs,
sideband for all CPUs is still needed. This is in preparation for allowing
system-wide events on all CPUs while the user requested events are on only
user requested CPUs.

Signed-off-by: Adrian Hunter <[email protected]>
Acked-by: Ian Rogers <[email protected]>
Acked-by: Namhyung Kim <[email protected]>
Cc: Alexey Bayduraev <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Leo Yan <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>

tools/perf/arch/x86/util/intel-pt.c

@@ -864,20 +864,22 @@ static int intel_pt_recording_options(struct auxtrace_record *itr,
 
 	/* Add dummy event to keep tracking */
 	if (opts->full_auxtrace) {
+		bool need_system_wide_tracking;
 		struct evsel *tracking_evsel;
 
-		err = parse_events(evlist, "dummy:u", NULL);
-		if (err)
-			return err;
+		/*
+		 * User space tasks can migrate between CPUs, so when tracing
+		 * selected CPUs, sideband for all CPUs is still needed.
+		 */
+		need_system_wide_tracking = evlist->core.has_user_cpus &&
+					    !intel_pt_evsel->core.attr.exclude_user;
 
-		tracking_evsel = evlist__last(evlist);
+		tracking_evsel = evlist__add_aux_dummy(evlist, need_system_wide_tracking);
+		if (!tracking_evsel)
+			return -ENOMEM;
 
 		evlist__set_tracking_event(evlist, tracking_evsel);
 
-		tracking_evsel->core.attr.freq = 0;
-		tracking_evsel->core.attr.sample_period = 1;
-
-		tracking_evsel->no_aux_samples = true;
 		if (need_immediate)
 			tracking_evsel->immediate = true;