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gh-135953: Add GIL contention markers to sampling profiler Gecko format #139485

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Merged
pablogsal merged 3 commits into from
Nov 17, 2025
Merged

gh-135953: Add GIL contention markers to sampling profiler Gecko format #139485

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7b2719e
gh-135953: Add GIL contention markers to sampling profiler Gecko format
pablogsal Oct 1, 2025
a332095
fixup! gh-135953: Add GIL contention markers to sampling profiler Gec…
pablogsal Oct 6, 2025
e739702
Fix GC markers
pablogsal Nov 1, 2025
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Fix GC markers
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@pablogsal
pablogsal committed Nov 1, 2025
commit e7397026fa61c820df2b961f7a8682f8cbb68316
61 changes: 18 additions & 43 deletions Lib/profiling/sampling/gecko_collector.py
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Original file line number Diff line number Diff line change
Expand Up @@ -84,8 +84,8 @@ def __init__(self, *, skip_idle=False):
self.native_code_start = {} # Thread running native code (on CPU without GIL)
self.gil_wait_start = {} # Thread waiting for GIL

# GC event tracking: track if we're currently in a GC
self.potential_gc_start = None
# GC event tracking: track GC start time per thread
self.gc_start_per_thread = {} # tid -> start_time

# Track which threads have been initialized for state tracking
self.initialized_threads = set()
Expand Down Expand Up @@ -136,17 +136,12 @@ def collect(self, stack_frames):
) / self.sample_count
self.last_sample_time = current_time

# GC Event Detection and process threads
gc_collecting = False

# Process threads and track GC per thread
for interpreter_info in stack_frames:
for thread_info in interpreter_info.threads:
# Track GC status
if thread_info.gc_collecting:
gc_collecting = True

frames = thread_info.frame_info
tid = thread_info.thread_id
gc_collecting = thread_info.gc_collecting

# Initialize thread if needed
if tid not in self.threads:
Expand Down Expand Up @@ -202,6 +197,19 @@ def collect(self, stack_frames):
self._add_marker(tid, "Waiting for GIL", self.gil_wait_start.pop(tid),
current_time, CATEGORY_GIL)

# Track GC events - attribute to all threads that hold the GIL during GC
# (GC is interpreter-wide but runs on whichever thread(s) have the GIL)
# If GIL switches during GC, multiple threads will get GC markers
if gc_collecting and has_gil:
# Start GC marker if not already started for this thread
if tid not in self.gc_start_per_thread:
self.gc_start_per_thread[tid] = current_time
elif tid in self.gc_start_per_thread:
# End GC marker if it was running for this thread
# (either GC finished or thread lost GIL)
self._add_marker(tid, "GC Collecting", self.gc_start_per_thread.pop(tid),
current_time, CATEGORY_GC)

# Mark thread as initialized after processing all state transitions
self.initialized_threads.add(tid)

Expand All @@ -224,17 +232,6 @@ def collect(self, stack_frames):
samples["time"].append(current_time)
samples["eventDelay"].append(None)

# Handle GC event markers after processing all threads
if gc_collecting:
if self.potential_gc_start is None:
# Start of GC
self.potential_gc_start = current_time
else:
# End of GC
if self.potential_gc_start is not None:
self._add_gc_marker(self.potential_gc_start, current_time)
self.potential_gc_start = None

self.sample_count += 1

def _create_thread(self, tid):
Expand Down Expand Up @@ -372,24 +369,6 @@ def _add_marker(self, tid, name, start_time, end_time, category):
"tid": tid
})

def _add_gc_marker(self, start_time, end_time):
"""Add a GC Collecting event marker to the main thread."""
if not self.threads:
return

# Find the main thread by checking isMainThread flag
main_tid = None
for tid, thread_data in self.threads.items():
if thread_data.get("isMainThread", False):
main_tid = tid
break

# If we can't find the main thread, use the first thread as fallback
if main_tid is None:
main_tid = next(iter(self.threads))

self._add_marker(main_tid, "GC Collecting", start_time, end_time, CATEGORY_GC)

def _process_stack(self, thread_data, frames):
"""Process a stack and return the stack index."""
if not frames:
Expand Down Expand Up @@ -571,18 +550,14 @@ def _finalize_markers(self):
(self.python_code_start, "Python Code", CATEGORY_CODE_TYPE),
(self.native_code_start, "Native Code", CATEGORY_CODE_TYPE),
(self.gil_wait_start, "Waiting for GIL", CATEGORY_GIL),
(self.gc_start_per_thread, "GC Collecting", CATEGORY_GC),
]

for state_dict, marker_name, category in marker_states:
for tid in list(state_dict.keys()):
self._add_marker(tid, marker_name, state_dict[tid], end_time, category)
del state_dict[tid]

# Close any open GC marker
if self.potential_gc_start is not None:
self._add_gc_marker(self.potential_gc_start, end_time)
self.potential_gc_start = None

def export(self, filename):
"""Export the profile to a Gecko JSON file."""

Expand Down
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