GH-140638: Add a GC "duration" stat (GH-141720)

Author: brandtbucher

Doc/library/gc.rst

@@ -108,10 +108,16 @@ The :mod:`gc` module provides the following functions:
 
    * ``uncollectable`` is the total number of objects which were found
      to be uncollectable (and were therefore moved to the :data:`garbage`
-     list) inside this generation.
+     list) inside this generation;
+
+   * ``duration`` is the total time in seconds spent in collections for this
+     generation.
 
    .. versionadded:: 3.4
 
+   .. versionchanged:: next
+      Add ``duration``.
+
 
 .. function:: set_threshold(threshold0, [threshold1, [threshold2]])
 
@@ -313,6 +319,9 @@ values but should not rebind them):
       "uncollectable": When *phase* is "stop", the number of objects
       that could not be collected and were put in :data:`garbage`.
 
+      "duration": When *phase* is "stop", the time in seconds spent in the
+      collection.
+
    Applications can add their own callbacks to this list.  The primary
    use cases are:
 
@@ -325,6 +334,9 @@ values but should not rebind them):
 
    .. versionadded:: 3.3
 
+   .. versionchanged:: next
+      Add "duration".
+
 
 The following constants are provided for use with :func:`set_debug`:
 

Include/internal/pycore_interp_structs.h

@@ -179,6 +179,8 @@ struct gc_collection_stats {
     Py_ssize_t collected;
     /* total number of uncollectable objects (put into gc.garbage) */
     Py_ssize_t uncollectable;
+    // Duration of the collection in seconds:
+    double duration;
 };
 
 /* Running stats per generation */
@@ -189,6 +191,8 @@ struct gc_generation_stats {
     Py_ssize_t collected;
     /* total number of uncollectable objects (put into gc.garbage) */
     Py_ssize_t uncollectable;
+    // Duration of the collection in seconds:
+    double duration;
 };
 
 enum _GCPhase {

Lib/test/test_gc.py

@@ -847,10 +847,11 @@ def test_get_stats(self):
         for st in stats:
             self.assertIsInstance(st, dict)
             self.assertEqual(set(st),
-                             {"collected", "collections", "uncollectable"})
+                             {"collected", "collections", "uncollectable", "duration"})
             self.assertGreaterEqual(st["collected"], 0)
             self.assertGreaterEqual(st["collections"], 0)
             self.assertGreaterEqual(st["uncollectable"], 0)
+            self.assertGreaterEqual(st["duration"], 0)
         # Check that collection counts are incremented correctly
         if gc.isenabled():
             self.addCleanup(gc.enable)
@@ -861,11 +862,25 @@ def test_get_stats(self):
         self.assertEqual(new[0]["collections"], old[0]["collections"] + 1)
         self.assertEqual(new[1]["collections"], old[1]["collections"])
         self.assertEqual(new[2]["collections"], old[2]["collections"])
+        self.assertGreater(new[0]["duration"], old[0]["duration"])
+        self.assertEqual(new[1]["duration"], old[1]["duration"])
+        self.assertEqual(new[2]["duration"], old[2]["duration"])
+        for stat in ["collected", "uncollectable"]:
+            self.assertGreaterEqual(new[0][stat], old[0][stat])
+            self.assertEqual(new[1][stat], old[1][stat])
+            self.assertEqual(new[2][stat], old[2][stat])
         gc.collect(2)
-        new = gc.get_stats()
-        self.assertEqual(new[0]["collections"], old[0]["collections"] + 1)
+        old, new = new, gc.get_stats()
+        self.assertEqual(new[0]["collections"], old[0]["collections"])
         self.assertEqual(new[1]["collections"], old[1]["collections"])
         self.assertEqual(new[2]["collections"], old[2]["collections"] + 1)
+        self.assertEqual(new[0]["duration"], old[0]["duration"])
+        self.assertEqual(new[1]["duration"], old[1]["duration"])
+        self.assertGreater(new[2]["duration"], old[2]["duration"])
+        for stat in ["collected", "uncollectable"]:
+            self.assertEqual(new[0][stat], old[0][stat])
+            self.assertEqual(new[1][stat], old[1][stat])
+            self.assertGreaterEqual(new[2][stat], old[2][stat])
 
     def test_freeze(self):
         gc.freeze()
@@ -1298,9 +1313,10 @@ def test_collect(self):
         # Check that we got the right info dict for all callbacks
         for v in self.visit:
             info = v[2]
-            self.assertTrue("generation" in info)
-            self.assertTrue("collected" in info)
-            self.assertTrue("uncollectable" in info)
+            self.assertIn("generation", info)
+            self.assertIn("collected", info)
+            self.assertIn("uncollectable", info)
+            self.assertIn("duration", info)
 
     def test_collect_generation(self):
         self.preclean()

Misc/NEWS.d/next/Core_and_Builtins/2025-11-18-07-45-37.gh-issue-140638.i06qxD.rst

@@ -0,0 +1,2 @@
+Expose a ``"duration"`` stat in :func:`gc.get_stats` and
+:data:`gc.callbacks`.

Modules/gcmodule.c

@@ -358,10 +358,11 @@ gc_get_stats_impl(PyObject *module)
     for (i = 0; i < NUM_GENERATIONS; i++) {
         PyObject *dict;
         st = &stats[i];
-        dict = Py_BuildValue("{snsnsn}",
+        dict = Py_BuildValue("{snsnsnsd}",
                              "collections", st->collections,
                              "collected", st->collected,
-                             "uncollectable", st->uncollectable
+                             "uncollectable", st->uncollectable,
+                             "duration", st->duration
                             );
         if (dict == NULL)
             goto error;

Python/gc.c

@@ -1363,6 +1363,7 @@ gc_list_set_space(PyGC_Head *list, int space)
 static void
 add_stats(GCState *gcstate, int gen, struct gc_collection_stats *stats)
 {
+    gcstate->generation_stats[gen].duration += stats->duration;
     gcstate->generation_stats[gen].collected += stats->collected;
     gcstate->generation_stats[gen].uncollectable += stats->uncollectable;
     gcstate->generation_stats[gen].collections += 1;
@@ -1387,7 +1388,6 @@ gc_collect_young(PyThreadState *tstate,
     validate_spaces(gcstate);
     gcstate->young.count = 0;
     gcstate->old[gcstate->visited_space].count++;
-    add_stats(gcstate, 0, stats);
     validate_spaces(gcstate);
 }
 
@@ -1701,7 +1701,6 @@ gc_collect_increment(PyThreadState *tstate, struct gc_collection_stats *stats)
     assert(gc_list_is_empty(&increment));
     gcstate->work_to_do -= increment_size;
 
-    add_stats(gcstate, 1, stats);
     if (gc_list_is_empty(not_visited)) {
         completed_scavenge(gcstate);
     }
@@ -1736,7 +1735,6 @@ gc_collect_full(PyThreadState *tstate,
     completed_scavenge(gcstate);
     _PyGC_ClearAllFreeLists(tstate->interp);
     validate_spaces(gcstate);
-    add_stats(gcstate, 2, stats);
 }
 
 /* This is the main function. Read this to understand how the
@@ -1846,10 +1844,11 @@ do_gc_callback(GCState *gcstate, const char *phase,
     assert(PyList_CheckExact(gcstate->callbacks));
     PyObject *info = NULL;
     if (PyList_GET_SIZE(gcstate->callbacks) != 0) {
-        info = Py_BuildValue("{sisnsn}",
+        info = Py_BuildValue("{sisnsnsd}",
             "generation", generation,
             "collected", stats->collected,
-            "uncollectable", stats->uncollectable);
+            "uncollectable", stats->uncollectable,
+            "duration", stats->duration);
         if (info == NULL) {
             PyErr_FormatUnraisable("Exception ignored while invoking gc callbacks");
             return;
@@ -2080,15 +2079,15 @@ _PyGC_Collect(PyThreadState *tstate, int generation, _PyGC_Reason reason)
     if (reason != _Py_GC_REASON_SHUTDOWN) {
         invoke_gc_callback(gcstate, "start", generation, &stats);
     }
-    PyTime_t t1;
     if (gcstate->debug & _PyGC_DEBUG_STATS) {
         PySys_WriteStderr("gc: collecting generation %d...\n", generation);
-        (void)PyTime_PerfCounterRaw(&t1);
         show_stats_each_generations(gcstate);
     }
     if (PyDTrace_GC_START_ENABLED()) {
         PyDTrace_GC_START(generation);
     }
+    PyTime_t start, stop;
+    (void)PyTime_PerfCounterRaw(&start);
     PyObject *exc = _PyErr_GetRaisedException(tstate);
     switch(generation) {
         case 0:
@@ -2103,6 +2102,9 @@ _PyGC_Collect(PyThreadState *tstate, int generation, _PyGC_Reason reason)
         default:
             Py_UNREACHABLE();
     }
+    (void)PyTime_PerfCounterRaw(&stop);
+    stats.duration = PyTime_AsSecondsDouble(stop - start);
+    add_stats(gcstate, generation, &stats);
     if (PyDTrace_GC_DONE_ENABLED()) {
         PyDTrace_GC_DONE(stats.uncollectable + stats.collected);
     }
@@ -2124,12 +2126,9 @@ _PyGC_Collect(PyThreadState *tstate, int generation, _PyGC_Reason reason)
     _Py_atomic_store_int(&gcstate->collecting, 0);
 
     if (gcstate->debug & _PyGC_DEBUG_STATS) {
-        PyTime_t t2;
-        (void)PyTime_PerfCounterRaw(&t2);
-        double d = PyTime_AsSecondsDouble(t2 - t1);
         PySys_WriteStderr(
             "gc: done, %zd unreachable, %zd uncollectable, %.4fs elapsed\n",
-            stats.collected + stats.uncollectable, stats.uncollectable, d
+            stats.collected + stats.uncollectable, stats.uncollectable, stats.duration
         );
     }
 

Python/gc_free_threading.c

@@ -1911,7 +1911,7 @@ handle_resurrected_objects(struct collection_state *state)
 static void
 invoke_gc_callback(PyThreadState *tstate, const char *phase,
                    int generation, Py_ssize_t collected,
-                   Py_ssize_t uncollectable)
+                   Py_ssize_t uncollectable, double duration)
 {
     assert(!_PyErr_Occurred(tstate));
 
@@ -1925,10 +1925,11 @@ invoke_gc_callback(PyThreadState *tstate, const char *phase,
     assert(PyList_CheckExact(gcstate->callbacks));
     PyObject *info = NULL;
     if (PyList_GET_SIZE(gcstate->callbacks) != 0) {
-        info = Py_BuildValue("{sisnsn}",
+        info = Py_BuildValue("{sisnsnsd}",
             "generation", generation,
             "collected", collected,
-            "uncollectable", uncollectable);
+            "uncollectable", uncollectable,
+            "duration", duration);
         if (info == NULL) {
             PyErr_FormatUnraisable("Exception ignored while "
                                    "invoking gc callbacks");
@@ -2340,7 +2341,6 @@ gc_collect_main(PyThreadState *tstate, int generation, _PyGC_Reason reason)
 {
     Py_ssize_t m = 0; /* # objects collected */
     Py_ssize_t n = 0; /* # unreachable objects that couldn't be collected */
-    PyTime_t t1 = 0;   /* initialize to prevent a compiler warning */
     GCState *gcstate = &tstate->interp->gc;
 
     // gc_collect_main() must not be called before _PyGC_Init
@@ -2372,19 +2372,19 @@ gc_collect_main(PyThreadState *tstate, int generation, _PyGC_Reason reason)
     GC_STAT_ADD(generation, collections, 1);
 
     if (reason != _Py_GC_REASON_SHUTDOWN) {
-        invoke_gc_callback(tstate, "start", generation, 0, 0);
+        invoke_gc_callback(tstate, "start", generation, 0, 0, 0);
     }
 
     if (gcstate->debug & _PyGC_DEBUG_STATS) {
         PySys_WriteStderr("gc: collecting generation %d...\n", generation);
         show_stats_each_generations(gcstate);
-        // ignore error: don't interrupt the GC if reading the clock fails
-        (void)PyTime_PerfCounterRaw(&t1);
     }
 
     if (PyDTrace_GC_START_ENABLED()) {
         PyDTrace_GC_START(generation);
     }
+    PyTime_t start, stop;
+    (void)PyTime_PerfCounterRaw(&start);
 
     PyInterpreterState *interp = tstate->interp;
 
@@ -2399,13 +2399,13 @@ gc_collect_main(PyThreadState *tstate, int generation, _PyGC_Reason reason)
     m = state.collected;
     n = state.uncollectable;
 
+    (void)PyTime_PerfCounterRaw(&stop);
+    double duration = PyTime_AsSecondsDouble(stop - start);
+
     if (gcstate->debug & _PyGC_DEBUG_STATS) {
-        PyTime_t t2;
-        (void)PyTime_PerfCounterRaw(&t2);
-        double d = PyTime_AsSecondsDouble(t2 - t1);
         PySys_WriteStderr(
             "gc: done, %zd unreachable, %zd uncollectable, %.4fs elapsed\n",
-            n+m, n, d);
+            n+m, n, duration);
     }
 
     // Clear the current thread's free-list again.
@@ -2426,6 +2426,7 @@ gc_collect_main(PyThreadState *tstate, int generation, _PyGC_Reason reason)
     stats->collections++;
     stats->collected += m;
     stats->uncollectable += n;
+    stats->duration += duration;
 
     GC_STAT_ADD(generation, objects_collected, m);
 #ifdef Py_STATS
@@ -2444,7 +2445,7 @@ gc_collect_main(PyThreadState *tstate, int generation, _PyGC_Reason reason)
     }
 
     if (reason != _Py_GC_REASON_SHUTDOWN) {
-        invoke_gc_callback(tstate, "stop", generation, m, n);
+        invoke_gc_callback(tstate, "stop", generation, m, n, duration);
     }
 
     assert(!_PyErr_Occurred(tstate));