linux-kernel - [PATCH v5 1/3] perf stat: Read tool events last

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Message-ID: <20251118211326.1840989-2-irogers@google.com>
Date: Tue, 18 Nov 2025 13:13:24 -0800
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>, 
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>, 
	Ian Rogers <irogers@...gle.com>, Adrian Hunter <adrian.hunter@...el.com>, 
	"Dr. David Alan Gilbert" <linux@...blig.org>, Yang Li <yang.lee@...ux.alibaba.com>, 
	James Clark <james.clark@...aro.org>, Thomas Falcon <thomas.falcon@...el.com>, 
	Thomas Richter <tmricht@...ux.ibm.com>, linux-perf-users@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Andi Kleen <ak@...ux.intel.com>, 
	Dapeng Mi <dapeng1.mi@...ux.intel.com>
Subject: [PATCH v5 1/3] perf stat: Read tool events last

When reading a metric like memory bandwidth on multiple sockets, the
additional sockets will be on CPUS > 0. Because of the affinity
reading, the counters are read on CPU 0 along with the time, then the
later sockets are read. This can lead to the later sockets having a
bandwidth larger than is possible for the period of time. To avoid
this move the reading of tool events to occur after all other events
are read.

Signed-off-by: Ian Rogers <irogers@...gle.com>
---
 tools/perf/builtin-stat.c | 45 +++++++++++++++++++++++++++++++++------
 1 file changed, 39 insertions(+), 6 deletions(-)

diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
index ca1c80c141b6..5c06e9b61821 100644
--- a/tools/perf/builtin-stat.c
+++ b/tools/perf/builtin-stat.c
@@ -366,7 +366,7 @@ static int read_counter_cpu(struct evsel *counter, int cpu_map_idx)
 	return 0;
 }
 
-static int read_affinity_counters(void)
+static int read_counters_with_affinity(void)
 {
 	struct evlist_cpu_iterator evlist_cpu_itr;
 	struct affinity saved_affinity, *affinity;
@@ -387,6 +387,9 @@ static int read_affinity_counters(void)
 		if (evsel__is_bpf(counter))
 			continue;
 
+		if (evsel__is_tool(counter))
+			continue;
+
 		if (!counter->err)
 			counter->err = read_counter_cpu(counter, evlist_cpu_itr.cpu_map_idx);
 	}
@@ -412,16 +415,46 @@ static int read_bpf_map_counters(void)
 	return 0;
 }
 
-static int read_counters(void)
+static int read_tool_counters(void)
 {
-	if (!stat_config.stop_read_counter) {
-		if (read_bpf_map_counters() ||
-		    read_affinity_counters())
-			return -1;
+	struct evsel *counter;
+
+	evlist__for_each_entry(evsel_list, counter) {
+		int idx;
+
+		if (!evsel__is_tool(counter))
+			continue;
+
+		perf_cpu_map__for_each_idx(idx, counter->core.cpus) {
+			if (!counter->err)
+				counter->err = read_counter_cpu(counter, idx);
+		}
 	}
 	return 0;
 }
 
+static int read_counters(void)
+{
+	int ret;
+
+	if (stat_config.stop_read_counter)
+		return 0;
+
+	// Read all BPF counters first.
+	ret = read_bpf_map_counters();
+	if (ret)
+		return ret;
+
+	// Read non-BPF and non-tool counters next.
+	ret = read_counters_with_affinity();
+	if (ret)
+		return ret;
+
+	// Read the tool counters last. This way the duration_time counter
+	// should always be greater than any other counter's enabled time.
+	return read_tool_counters();
+}
+
 static void process_counters(void)
 {
 	struct evsel *counter;
-- 
2.52.0.rc1.455.g30608eb744-goog