From 928ca754b54af8ff9bca7ca9419978e826e2ef4e Mon Sep 17 00:00:00 2001
From: "Gabriele N. Tornetta" <gabriele.tornetta@datadoghq.com>
Date: Fri, 9 Oct 2026 12:39:55 +0100
Subject: [PATCH] fix: exclude idle samples from CPU stats

In full mode, AustinStats counted the time of idle samples towards CPU
statistics, making them identical to wall time. Idle samples now only
contribute to wall time, consistent with the speedscope and pprof
exporters.
---
 austin/stats.py                 |  5 ++++-
 test/stats/test_austin_stats.py | 37 +++++++++++++++++++++++++++++++++
 2 files changed, 41 insertions(+), 1 deletion(-)

diff --git a/austin/stats.py b/austin/stats.py
index f1d64cc..72614db 100644
--- a/austin/stats.py
+++ b/austin/stats.py
@@ -270,8 +270,11 @@ def update(self, sample: AustinSample) -> None:
         by using :func:`Sample.parse` on a sample string passed by Austin to
         the sample callback.
         """
-        if self.stats_type in {AustinStatsType.WALL, AustinStatsType.CPU}:
+        if self.stats_type is AustinStatsType.WALL:
             metric = sample.metrics.time
+        elif self.stats_type is AustinStatsType.CPU:
+            # In full mode, idle samples contribute wall time but no CPU time
+            metric = None if sample.idle else sample.metrics.time
         elif (
             self.stats_type is AustinStatsType.MEMORY_ALLOC
             and sample.metrics.memory is not None
diff --git a/test/stats/test_austin_stats.py b/test/stats/test_austin_stats.py
index 3f18deb..19313d7 100644
--- a/test/stats/test_austin_stats.py
+++ b/test/stats/test_austin_stats.py
@@ -25,6 +25,7 @@
 from copy import deepcopy
 
 from austin.events import AustinFrame
+from austin.events import AustinMetadata
 from austin.events import AustinMetrics
 from austin.events import AustinSample
 from austin.format.collapsed_stack import AustinFileReader
@@ -348,3 +349,39 @@ def test_deepcopy():
     cloned_stats = deepcopy(stats)
     assert cloned_stats == stats
     assert cloned_stats is not stats
+
+
+def test_load_full_mode_cpu_excludes_idle():
+    frames = (AustinFrame("foo_module.py", "foo", 10),)
+    stats = AustinStats.load(
+        iter(
+            [
+                AustinMetadata("mode", "full"),
+                AustinSample(
+                    pid=42,
+                    iid=0,
+                    thread="0x7f45645646",
+                    metrics=AustinMetrics(time=100, memory=10),
+                    frames=frames,
+                    idle=False,
+                ),
+                AustinSample(
+                    pid=42,
+                    iid=0,
+                    thread="0x7f45645646",
+                    metrics=AustinMetrics(time=900, memory=-5),
+                    frames=frames,
+                    idle=True,
+                ),
+            ]
+        )
+    )
+
+    def total(stats_type: AustinStatsType) -> int:
+        thread_info = ThreadInfo("0x7f45645646", 0)
+        return stats[stats_type].processes[42].threads[thread_info].total
+
+    assert total(AustinStatsType.CPU) == 100
+    assert total(AustinStatsType.WALL) == 1000
+    assert total(AustinStatsType.MEMORY_ALLOC) == 10
+    assert total(AustinStatsType.MEMORY_DEALLOC) == 5