gh-155591: Fix flame graph sample-time conversion in profiling.sampling

Lib/profiling/sampling/_flamegraph_assets/flamegraph.js

@@ -2,13 +2,22 @@ const EMBEDDED_DATA = {{FLAMEGRAPH_DATA}};
 
 // Global string table for resolving string indices
 let stringTable = [];
+// Duration of a single sample, in microseconds; node values are sample counts.
+let sampleIntervalUsec = EMBEDDED_DATA?.stats?.sample_interval_usec;
 let normalData = null;
 let invertedData = null;
 let currentThreadFilter = 'all';
 let isInverted = false;
 let useModuleNames = true;
 let zoomedNodeValue = null;
 
+// Convert a sample count into wall-clock milliseconds. Returns "--" when the
+// sampling interval is unknown, since a sample count is not a time.
+function formatSampleMs(samples) {
+  if (sampleIntervalUsec <= 0) return "--";
+  return ((samples * sampleIntervalUsec) / 1_000).toFixed(2);
+}
+
 // Heat colors are now defined in CSS variables (--heat-1 through --heat-8)
 // and automatically switch with theme changes - no JS color arrays needed!
 
@@ -260,7 +269,7 @@ function updateStatusBar(nodeData, rootValue) {
   const filename = resolveString(nodeData.filename) || "";
   const moduleName = resolveString(nodeData.module) || "";
   const lineno = nodeData.lineno;
-  const timeMs = (nodeData.value / 1000).toFixed(2);
+  const timeMs = formatSampleMs(nodeData.value);
   const percent = rootValue > 0 ? ((nodeData.value / rootValue) * 100).toFixed(1) : "0.0";
 
   const brandEl = document.getElementById('status-brand');
@@ -322,9 +331,9 @@ function createPythonTooltip(data) {
         .style("opacity", 0);
     }
 
-    const timeMs = (d.data.value / 1000).toFixed(2);
+    const timeMs = formatSampleMs(d.data.value);
     const selfSamples = d.data.self || 0;
-    const selfMs = (selfSamples / 1000).toFixed(2);
+    const selfMs = formatSampleMs(selfSamples);
     const percentage = ((d.data.value / data.value) * 100).toFixed(2);
     const relativePercentage = Math.min(100, ((d.data.value / (zoomedNodeValue ?? data.value)) * 100)).toFixed(2);
     const calls = d.data.calls || 0;
@@ -408,9 +417,9 @@ function createPythonTooltip(data) {
     // Differential stats section
     let diffSection = "";
     if (d.data.diff !== undefined && d.data.baseline !== undefined) {
-      const baselineSelf = (d.data.baseline / 1000).toFixed(2);
-      const currentSelf = ((d.data.self_time || 0) / 1000).toFixed(2);
-      const diffMs = (d.data.diff / 1000).toFixed(2);
+      const baselineSelf = formatSampleMs(d.data.baseline);
+      const currentSelf = formatSampleMs(d.data.self_time || 0);
+      const diffMs = formatSampleMs(d.data.diff);
       const diffPct = d.data.diff_pct;
       const sign = d.data.diff >= 0 ? "+" : "";
       const diffClass = d.data.diff > 0 ? "regression" : (d.data.diff < 0 ? "improvement" : "neutral");

Lib/profiling/sampling/stack_collector.py

@@ -371,6 +371,7 @@ def convert_children(children, min_samples, path_info):
             old_label = self._string_table.get_string(main_child["label"])
             main_child["label"] = self._string_table.intern(f"Program Root: {old_label}")
             main_child["stats"] = {
+                "sample_interval_usec": self.sample_interval_usec,
                 **self.stats,
                 "thread_stats": thread_stats,
                 "per_thread_stats": per_thread_stats_with_pct
@@ -387,6 +388,7 @@ def convert_children(children, min_samples, path_info):
             "value": total_samples,
             "children": root_children,
             "stats": {
+                "sample_interval_usec": self.sample_interval_usec,
                 **self.stats,
                 "thread_stats": thread_stats,
                 "per_thread_stats": per_thread_stats_with_pct

Lib/test/test_profiling/test_sampling_profiler/test_collectors.py

@@ -1336,6 +1336,31 @@ def test_flamegraph_collector_json_structure_includes_stats(self):
             self.assertIn("gc_pct", thread_data)
             self.assertIn("total", thread_data)
 
+    def test_flamegraph_stats_always_include_sample_interval(self):
+        """The sampling interval is needed to turn sample counts into times."""
+        collector = FlamegraphCollector(sample_interval_usec=250)
+
+        stack_frames = [
+            MockInterpreterInfo(
+                0,
+                [MockThreadInfo(1, [MockFrameInfo("a.py", 1, "func_a")])],
+            )
+        ]
+        collector.collect(stack_frames)
+
+        # No set_stats() call: the interval must still be reported.
+        data = collector._convert_to_flamegraph_format()
+        self.assertEqual(data["stats"]["sample_interval_usec"], 250)
+
+        collector.set_stats(
+            sample_interval_usec=250,
+            duration_sec=1.0,
+            sample_rate=4000.0,
+            mode=PROFILING_MODE_WALL,
+        )
+        data = collector._convert_to_flamegraph_format()
+        self.assertEqual(data["stats"]["sample_interval_usec"], 250)
+
     def test_flamegraph_nodes_include_per_thread_values(self):
         collector = FlamegraphCollector(sample_interval_usec=1000)
         root = MockFrameInfo("app.py", 1, "main")

Misc/NEWS.d/next/Library/2026-08-11-21-40-00.gh-issue-155591.Kq3vRt.rst

@@ -0,0 +1,5 @@
+Fix the times shown in :mod:`profiling.sampling` flame graph tooltips and status
+bar.  Sample counts were divided by 1000 and labelled as milliseconds, so the
+reported times were wrong by a factor of the sampling interval.  They are now
+converted using the actual interval, which is always recorded in the exported
+data.