perf record: Set PERF_FORMAT_LOST by default

As we want to see the number of lost samples in the perf report, set the
LOST format when it configs evsel.  On old kernels, it'd fallback to
disable it.
Reviewed-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20220901195739.668604-3-namhyung@kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/evsel.c

@@ -1161,6 +1161,7 @@ void evsel__config(struct evsel *evsel, struct record_opts *opts,
 	attr->sample_id_all = perf_missing_features.sample_id_all ? 0 : 1;
 	attr->inherit	    = !opts->no_inherit;
 	attr->write_backward = opts->overwrite ? 1 : 0;
+	attr->read_format   = PERF_FORMAT_LOST;
 
 	evsel__set_sample_bit(evsel, IP);
 	evsel__set_sample_bit(evsel, TID);
@@ -1856,6 +1857,8 @@ static int __evsel__prepare_open(struct evsel *evsel, struct perf_cpu_map *cpus,
 
 static void evsel__disable_missing_features(struct evsel *evsel)
 {
+	if (perf_missing_features.read_lost)
+		evsel->core.attr.read_format &= ~PERF_FORMAT_LOST;
 	if (perf_missing_features.weight_struct) {
 		evsel__set_sample_bit(evsel, WEIGHT);
 		evsel__reset_sample_bit(evsel, WEIGHT_STRUCT);
@@ -1907,7 +1910,12 @@ bool evsel__detect_missing_features(struct evsel *evsel)
 	 * Must probe features in the order they were added to the
 	 * perf_event_attr interface.
 	 */
-	if (!perf_missing_features.weight_struct &&
+	if (!perf_missing_features.read_lost &&
+	    (evsel->core.attr.read_format & PERF_FORMAT_LOST)) {
+		perf_missing_features.read_lost = true;
+		pr_debug2("switching off PERF_FORMAT_LOST support\n");
+		return true;
+	} else if (!perf_missing_features.weight_struct &&
 	    (evsel->core.attr.sample_type & PERF_SAMPLE_WEIGHT_STRUCT)) {
 		perf_missing_features.weight_struct = true;
 		pr_debug2("switching off weight struct support\n");

tools/perf/util/evsel.h

@@ -188,6 +188,7 @@ struct perf_missing_features {
 	bool data_page_size;
 	bool code_page_size;
 	bool weight_struct;
+	bool read_lost;
 };
 
 extern struct perf_missing_features perf_missing_features;