linux-kernel - [PATCH v1 02/13] perf perf_api_probe: Avoid scanning all PMUs, try software PMU first

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Message-ID: <20250828064231.1762997-3-irogers@google.com>
Date: Wed, 27 Aug 2025 23:42:20 -0700
From: Ian Rogers <irogers@...gle.com>
To: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, 
	Arnaldo Carvalho de Melo <acme@...nel.org>, Namhyung Kim <namhyung@...nel.org>, 
	Mark Rutland <mark.rutland@....com>, 
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>, 
	Ian Rogers <irogers@...gle.com>, Adrian Hunter <adrian.hunter@...el.com>, 
	Kan Liang <kan.liang@...ux.intel.com>, James Clark <james.clark@...aro.org>, 
	Xu Yang <xu.yang_2@....com>, Thomas Falcon <thomas.falcon@...el.com>, 
	Andi Kleen <ak@...ux.intel.com>, linux-kernel@...r.kernel.org, 
	linux-perf-users@...r.kernel.org, bpf@...r.kernel.org, 
	Atish Patra <atishp@...osinc.com>, Beeman Strong <beeman@...osinc.com>, Leo Yan <leo.yan@....com>
Subject: [PATCH v1 02/13] perf perf_api_probe: Avoid scanning all PMUs, try
 software PMU first

Scan the software PMU first rather than last as it is the least likely
to fail the probe. Specifying the software PMU by name was enabled by
commit 9957d8c801fe ("perf jevents: Add common software event
json"). For hardware events, add core PMU names when getting events to
probe so that not all PMUs are scanned. For example, when legacy
events support wildcards and for the event "cycles:u" on x86, we want
to only scan the "cpu" PMU and not all uncore PMUs for the event too.

Signed-off-by: Ian Rogers <irogers@...gle.com>
---
 tools/perf/util/perf_api_probe.c | 27 +++++++++++++++++++--------
 1 file changed, 19 insertions(+), 8 deletions(-)

diff --git a/tools/perf/util/perf_api_probe.c b/tools/perf/util/perf_api_probe.c
index 1de3b69cdf4a..6ecf38314f01 100644
--- a/tools/perf/util/perf_api_probe.c
+++ b/tools/perf/util/perf_api_probe.c
@@ -59,10 +59,10 @@ static int perf_do_probe_api(setup_probe_fn_t fn, struct perf_cpu cpu, const cha
 
 static bool perf_probe_api(setup_probe_fn_t fn)
 {
-	const char *try[] = {"cycles:u", "instructions:u", "cpu-clock:u", NULL};
+	struct perf_pmu *pmu;
 	struct perf_cpu_map *cpus;
 	struct perf_cpu cpu;
-	int ret, i = 0;
+	int ret = 0;
 
 	cpus = perf_cpu_map__new_online_cpus();
 	if (!cpus)
@@ -70,12 +70,23 @@ static bool perf_probe_api(setup_probe_fn_t fn)
 	cpu = perf_cpu_map__cpu(cpus, 0);
 	perf_cpu_map__put(cpus);
 
-	do {
-		ret = perf_do_probe_api(fn, cpu, try[i++]);
-		if (!ret)
-			return true;
-	} while (ret == -EAGAIN && try[i]);
-
+	ret = perf_do_probe_api(fn, cpu, "software/cpu-clock/u");
+	if (!ret)
+		return true;
+
+	pmu = perf_pmus__scan_core(/*pmu=*/NULL);
+	if (pmu) {
+		const char *try[] = {"cycles", "instructions", NULL};
+		char buf[256];
+		int i = 0;
+
+		while (ret == -EAGAIN && try[i]) {
+			snprintf(buf, sizeof(buf), "%s/%s/u", pmu->name, try[i++]);
+			ret = perf_do_probe_api(fn, cpu, buf);
+			if (!ret)
+				return true;
+		}
+	}
 	return false;
 }
 
-- 
2.51.0.268.g9569e192d0-goog