[PATCH 2/5] perf record: Set PERF_FORMAT_LOST by default

[Namhyung Kim <namhyung@kernel.org>]

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.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
---
 tools/perf/util/evsel.c | 10 +++++++++-
 tools/perf/util/evsel.h |  1 +
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index e1bc76ece117..5776bfa70f11 100644
--- a/tools/perf/util/evsel.c
+++ b/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");
diff --git a/tools/perf/util/evsel.h b/tools/perf/util/evsel.h
index d927713b513e..989865e16aad 100644
--- a/tools/perf/util/evsel.h
+++ b/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;
-- 
2.37.2.789.g6183377224-goog