From: Ian Rogers <irogers@google.com>
Date: Wed, 18 Mar 2026 23:45:56 +0000 (-0700)
Subject: perf evsel: Improve falling back from cycles
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=d84db579d75fd32ea6dd7814c8cf6b1c8b45ac05;p=thirdparty%2Fkernel%2Fstable.git

perf evsel: Improve falling back from cycles

Switch to using evsel__match rather than comparing perf_event_attr
values, this is robust on hybrid architectures.
Ensure evsel->pmu matches the evsel->core.attr.
Remove exclude bits that get set in other fallback attempts when
switching the event.
Log the event name with modifiers when switching the event on fallback.

Signed-off-by: Ian Rogers <irogers@google.com>
Tested-by: Thomas Richter <tmricht@linux.ibm.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
---

diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index f59228c1a39e..bd14d9bbc91f 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -3785,25 +3785,42 @@ bool evsel__fallback(struct evsel *evsel, struct target *target, int err,
 {
 	int paranoid;
 
-	if ((err == ENOENT || err == ENXIO || err == ENODEV) &&
-	    evsel->core.attr.type   == PERF_TYPE_HARDWARE &&
-	    evsel->core.attr.config == PERF_COUNT_HW_CPU_CYCLES) {
+	if ((err == ENODEV || err == ENOENT || err == ENXIO) &&
+	    evsel__match(evsel, HARDWARE, HW_CPU_CYCLES)) {
 		/*
-		 * If it's cycles then fall back to hrtimer based cpu-clock sw
-		 * counter, which is always available even if no PMU support.
-		 *
-		 * PPC returns ENXIO until 2.6.37 (behavior changed with commit
-		 * b0a873e).
+		 * If it's the legacy hardware cycles event fails then fall back
+		 * to hrtimer based cpu-clock sw counter, which is always
+		 * available even if no PMU support. PPC returned ENXIO rather
+		 * than ENODEV or ENOENT until 2.6.37.
 		 */
-		evsel->core.attr.type   = PERF_TYPE_SOFTWARE;
+		evsel->pmu = perf_pmus__find_by_type(PERF_TYPE_SOFTWARE);
+		assert(evsel->pmu); /* software is a "well-known" and can't fail PMU type. */
+
+		/* Configure the event. */
+		evsel->core.attr.type = PERF_TYPE_SOFTWARE;
 		evsel->core.attr.config = target__has_cpu(target)
 			? PERF_COUNT_SW_CPU_CLOCK
 			: PERF_COUNT_SW_TASK_CLOCK;
-		scnprintf(msg, msgsize,
-			"The cycles event is not supported, trying to fall back to %s",
-			target__has_cpu(target) ? "cpu-clock" : "task-clock");
+		evsel->core.is_pmu_core = false;
+
+		/* Remove excludes for new event. */
+		if (evsel->fallenback_eacces) {
+			evsel->core.attr.exclude_kernel = 0;
+			evsel->core.attr.exclude_hv     = 0;
+			evsel->fallenback_eacces = false;
+		}
+		if (evsel->fallenback_eopnotsupp) {
+			evsel->core.attr.exclude_guest = 0;
+			evsel->fallenback_eopnotsupp = false;
+		}
 
+		/* Name is recomputed by evsel__name. */
 		zfree(&evsel->name);
+
+		/* Log message. */
+		scnprintf(msg, msgsize,
+			  "The cycles event is not supported, trying to fall back to %s",
+			  evsel__name(evsel));
 		return true;
 	} else if (err == EACCES && !evsel->core.attr.exclude_kernel &&
 		   (paranoid = perf_event_paranoid()) > 1) {
@@ -3830,7 +3847,7 @@ bool evsel__fallback(struct evsel *evsel, struct target *target, int err,
 			  " samples", paranoid);
 		evsel->core.attr.exclude_kernel = 1;
 		evsel->core.attr.exclude_hv     = 1;
-
+		evsel->fallenback_eacces = true;
 		return true;
 	} else if (err == EOPNOTSUPP && !evsel->core.attr.exclude_guest &&
 		   !evsel->exclude_GH) {
@@ -3851,7 +3868,7 @@ bool evsel__fallback(struct evsel *evsel, struct target *target, int err,
 		/* Apple M1 requires exclude_guest */
 		scnprintf(msg, msgsize, "Trying to fall back to excluding guest samples");
 		evsel->core.attr.exclude_guest = 1;
-
+		evsel->fallenback_eopnotsupp = true;
 		return true;
 	}
 no_fallback:
diff --git a/tools/perf/util/evsel.h b/tools/perf/util/evsel.h
index a3d754c029a0..97f57fab28ce 100644
--- a/tools/perf/util/evsel.h
+++ b/tools/perf/util/evsel.h
@@ -124,6 +124,8 @@ struct evsel {
 	bool			default_metricgroup; /* A member of the Default metricgroup */
 	bool			default_show_events; /* If a default group member, show the event */
 	bool			needs_uniquify;
+	bool			fallenback_eacces;
+	bool			fallenback_eopnotsupp;
 	struct hashmap		*per_pkg_mask;
 	int			err;
 	int			script_output_type;