[PATCH v6 29/59] perf futex-contention: Port futex-contention to use python module

Ian Rogers
2026-04-25T17:49:59Z

Rewrite tools/perf/scripts/python/futex-contention.py to use the
python module and various style changes. By avoiding the overheads in
the `perf script` execution the performance improves by more than 3.2x
as shown in the following (with PYTHON_PATH and PERF_EXEC_PATH set as
necessary):

```
$ perf record -e syscalls:sys_*_futex -a sleep 1
...
$ time perf script tools/perf/scripts/python/futex-contention.py
Install the python-audit package to get syscall names.
For example:
# apt-get install python3-audit (Ubuntu)
# yum install python3-audit (Fedora)
etc.

Press control+C to stop and show the summary
aaa/4[2435653] lock 7f76b380c878 contended 1 times, 1099 avg ns [max: 1099 ns, min 1099 ns]
...
real 0m1.007s
user 0m0.935s
sys 0m0.072s
$ time python3 tools/perf/python/futex-contention.py
...
real 0m0.314s
user 0m0.259s
sys 0m0.056s
```

Assisted-by: Gemini:gemini-3.1-pro-preview
Signed-off-by: Ian Rogers <irogers@google.com>
---
v2:

1. Fixed Module Import Failure: Corrected the type annotations from
[int, int] to Tuple[int, int] . The previous code would raise a
TypeError at module import time because lists cannot be used as
types in dictionary annotations.

2. Prevented Out-Of-Memory Crashes: Replaced the approach of storing
every single duration in a list with a LockStats class that
maintains running aggregates (count, total time, min, max). This
ensures O(1) memory usage per lock/thread pair rather than
unbounded memory growth.

3. Support for Custom Input Files: Added a -i / --input command-line
argument to support processing arbitrarily named trace files,
removing the hardcoded "perf.data" restriction.

4. Robust Process Lookup: Added a check to ensure session is
initialized before calling session. process() , preventing
potential NoneType attribute errors if events are processed during
initialization.
---
tools/perf/python/futex-contention.py | 87 +++++++++++++++++++++++++++
1 file changed, 87 insertions(+)
create mode 100755 tools/perf/python/futex-contention.py

diff --git a/tools/perf/python/futex-contention.py b/tools/perf/python/futex-contention.py
new file mode 100755
index 000000000000..1fc87ec0e6e5
--- /dev/null
+++ b/tools/perf/python/futex-contention.py
@@ -0,0 +1,87 @@
+#!/usr/bin/env python3
+# SPDX-License-Identifier: GPL-2.0
+"""Measures futex contention."""
+
+import argparse
+from collections import defaultdict
+from typing import Dict, Tuple
+import perf
+
+class LockStats:
+ """Aggregate lock contention information."""
+ def __init__(self) -> None:
+ self.count = 0
+ self.total_time = 0
+ self.min_time = 0
+ self.max_time = 0
+
+ def add(self, duration: int) -> None:
+ """Add a new duration measurement."""
+ self.count += 1
+ self.total_time += duration
+ if self.count == 1:
+ self.min_time = duration
+ self.max_time = duration
+ else:
+ self.min_time = min(self.min_time, duration)
+ self.max_time = max(self.max_time, duration)
+
+ def avg(self) -> float:
+ """Return average duration."""
+ return self.total_time / self.count if self.count > 0 else 0.0
+
+process_names: Dict[int, str] = {}
+start_times: Dict[int, Tuple[int, int]] = {}
+session = None
+durations: Dict[Tuple[int, int], LockStats] = defaultdict(LockStats)
+
+FUTEX_WAIT = 0
+FUTEX_WAKE = 1
+FUTEX_PRIVATE_FLAG = 128
+FUTEX_CLOCK_REALTIME = 256
+FUTEX_CMD_MASK = ~(FUTEX_PRIVATE_FLAG | FUTEX_CLOCK_REALTIME)
+
+
+def process_event(sample: perf.sample_event) -> None:
+ """Process a single sample event."""
+ def handle_start(tid: int, uaddr: int, op: int, start_time: int) -> None:
+ if (op & FUTEX_CMD_MASK) != FUTEX_WAIT:
+ return
+ if tid not in process_names:
+ try:
+ if session:
+ process = session.find_thread(tid)
+ if process:
+ process_names[tid] = process.comm()
+ except (TypeError, AttributeError):
+ return
+ start_times[tid] = (uaddr, start_time)
+
+ def handle_end(tid: int, end_time: int) -> None:
+ if tid not in start_times:
+ return
+ (uaddr, start_time) = start_times[tid]
+ del start_times[tid]
+ durations[(tid, uaddr)].add(end_time - start_time)
+
+ event_name = str(sample.evsel)
+ if event_name == "evsel(syscalls:sys_enter_futex)":
+ uaddr = getattr(sample, "uaddr", 0)
+ op = getattr(sample, "op", 0)
+ handle_start(sample.sample_tid, uaddr, op, sample.sample_time)
+ elif event_name == "evsel(syscalls:sys_exit_futex)":
+ handle_end(sample.sample_tid, sample.sample_time)
+
+
+if __name__ == "__main__":
+ ap = argparse.ArgumentParser(description="Measure futex contention")
+ ap.add_argument("-i", "--input", default="perf.data", help="Input file name")
+ args = ap.parse_args()
+
+ session = perf.session(perf.data(args.input), sample=process_event)
+ session.process_events()
+
+ for ((t, u), stats) in sorted(durations.items()):
+ avg_ns = stats.avg()
+ print(f"{process_names.get(t, 'unknown')}[{t}] lock {u:x} contended {stats.count} times, "
+ f"{avg_ns:.0f} avg ns [max: {stats.max_time} ns, min {stats.min_time} ns]")
--
2.54.0.545.g6539524ca2-goog