linux-kernel - [PATCH v2 4/4] tools/perf: Allow inherit + inherit_stat + PERF_SAMPLE

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Date: Thu,  8 Feb 2024 13:10:50 +0000
From: Ben Gainey <ben.gainey@....com>
To: linux-perf-users@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc: peterz@...radead.org,
	mingo@...hat.com,
	acme@...nel.org,
	mark.rutland@....com,
	alexander.shishkin@...ux.intel.com,
	jolsa@...nel.org,
	namhyung@...nel.org,
	irogers@...gle.com,
	adrian.hunter@...el.com,
	james.clark@....com,
	Ben Gainey <ben.gainey@....com>
Subject: [PATCH v2 4/4] tools/perf: Allow inherit + inherit_stat + PERF_SAMPLE_READ when opening events

When PERF_SAMPLE_READ is used will enable inherit_stat when inherit is set.

Provides a fallback path to disable inherit when this feature is not available,
which is inline with the previous behaviour.

Signed-off-by: Ben Gainey <ben.gainey@....com>
---
 tools/perf/util/evsel.c | 15 +++++++++++++--
 tools/perf/util/evsel.h |  1 +
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index 6d7c9c58a9bc..dc74b39a2254 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -1156,7 +1156,11 @@ void evsel__config(struct evsel *evsel, struct record_opts *opts,
 		 */
 		if (leader->core.nr_members > 1) {
 			attr->read_format |= PERF_FORMAT_GROUP;
-			attr->inherit = 0;
+		}
+
+		/* Inherit + READ requires inherit_stat */
+		if (attr->inherit) {
+			attr->inherit_stat = true;
 		}
 	}
 
@@ -1832,6 +1836,8 @@ 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.inherit_sample_read)
+		evsel->core.attr.inherit = 0;
 	if (perf_missing_features.branch_counters)
 		evsel->core.attr.branch_sample_type &= ~PERF_SAMPLE_BRANCH_COUNTERS;
 	if (perf_missing_features.read_lost)
@@ -1887,7 +1893,12 @@ 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.branch_counters &&
+	if (!perf_missing_features.inherit_sample_read &&
+	    evsel->core.attr.inherit && (evsel->core.attr.sample_type & PERF_SAMPLE_READ)) {
+		perf_missing_features.inherit_sample_read = true;
+		pr_debug2("Using PERF_SAMPLE_READ / :S modifier is not compatible with inherit, falling back to no-inherit.\n");
+		return true;
+	} else if (!perf_missing_features.branch_counters &&
 	    (evsel->core.attr.branch_sample_type & PERF_SAMPLE_BRANCH_COUNTERS)) {
 		perf_missing_features.branch_counters = true;
 		pr_debug2("switching off branch counters support\n");
diff --git a/tools/perf/util/evsel.h b/tools/perf/util/evsel.h
index efbb6e848287..11cc9b8bee27 100644
--- a/tools/perf/util/evsel.h
+++ b/tools/perf/util/evsel.h
@@ -192,6 +192,7 @@ struct perf_missing_features {
 	bool weight_struct;
 	bool read_lost;
 	bool branch_counters;
+	bool inherit_sample_read;
 };
 
 extern struct perf_missing_features perf_missing_features;
-- 
2.43.0