[PATCH v7 49/59] perf rw-by-pid: Port rw-by-pid to use python module

Ian Rogers
2026-04-25T22:53:18Z

Port the legacy Perl script rw-by-pid.pl to a python script using the
perf module in tools/perf/python.

The new script uses a class-based architecture and leverages the
perf.session API for event processing.

It tracks read and write activity by PID for all processes,
aggregating bytes requested, bytes read, total reads, and errors.

Complications:
- Refactored process_event to extract helper methods
(_handle_sys_enter_read, etc.) to reduce the number of branches and
satisfy pylint.
- Split long lines to comply with line length limits.
- pylint warns about the module name not being snake_case, but it is
kept for consistency with the original script name.

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

- Fixed Substring Matching: Replaced loose substring checks like if
"sys_enter_read" in event_name: with exact matches against
syscalls:sys_enter_read and raw_syscalls:sys_enter_read using
sample.evsel.name . This prevents unrelated syscalls with similar
names (like readahead ) from being incorrectly aggregated. Similar
fixes were applied for exit events and write events.

- Inlined Handlers and Tracked Errors: Inlined the _handle_sys_*
helper methods into process_event() to make error handling
easier. Now, if a sample lacks expected fields (raising
AttributeError ), it is added to the self.unhandled tracker instead
of being silently dropped, providing better visibility to the user.

- Code Cleanup: Fixed trailing whitespace and added a pylint disable
comment for too-many-branches caused by the inlining.

v6:
- Fixed `AttributeError` by using `str(sample.evsel)` to get event name.
---
tools/perf/python/rw-by-pid.py | 158 +++++++++++++++++++++++++++++++++
1 file changed, 158 insertions(+)
create mode 100755 tools/perf/python/rw-by-pid.py

diff --git a/tools/perf/python/rw-by-pid.py b/tools/perf/python/rw-by-pid.py
new file mode 100755
index 000000000000..b206d2a575cd
--- /dev/null
+++ b/tools/perf/python/rw-by-pid.py
@@ -0,0 +1,158 @@
+#!/usr/bin/env python3
+# SPDX-License-Identifier: GPL-2.0-only
+"""Display r/w activity for all processes."""
+
+import argparse
+from collections import defaultdict
+import sys
+from typing import Optional, Dict, List, Tuple, Any
+import perf
+
+class RwByPid:
+ """Tracks and displays read/write activity by PID."""
+ def __init__(self) -> None:
+ self.reads: Dict[int, Dict[str, Any]] = defaultdict(
+ lambda: {
+ "bytes_requested": 0,
+ "bytes_read": 0,
+ "total_reads": 0,
+ "comm": "",
+ "errors": defaultdict(int),
+ }
+ )
+ self.writes: Dict[int, Dict[str, Any]] = defaultdict(
+ lambda: {
+ "bytes_written": 0,
+ "total_writes": 0,
+ "comm": "",
+ "errors": defaultdict(int),
+ }
+ )
+ self.unhandled: Dict[str, int] = defaultdict(int)
+ self.session: Optional[perf.session] = None
+
+ def process_event(self, sample: perf.sample_event) -> None: # pylint: disable=too-many-branches
+ """Process events."""
+ event_name = str(sample.evsel)[6:-1]
+ pid = sample.sample_pid
+
+ assert self.session is not None
+ try:
+ comm = self.session.find_thread(pid).comm()
+ except Exception: # pylint: disable=broad-except
+ comm = "unknown"
+
+ if event_name in ("syscalls:sys_enter_read", "raw_syscalls:sys_enter_read"):
+ try:
+ count = sample.count
+ self.reads[pid]["bytes_requested"] += count
+ self.reads[pid]["total_reads"] += 1
+ self.reads[pid]["comm"] = comm
+ except AttributeError:
+ self.unhandled[event_name] += 1
+ elif event_name in ("syscalls:sys_exit_read", "raw_syscalls:sys_exit_read"):
+ try:
+ ret = sample.ret
+ if ret > 0:
+ self.reads[pid]["bytes_read"] += ret
+ else:
+ self.reads[pid]["errors"][ret] += 1
+ except AttributeError:
+ self.unhandled[event_name] += 1
+ elif event_name in ("syscalls:sys_enter_write", "raw_syscalls:sys_enter_write"):
+ try:
+ count = sample.count
+ self.writes[pid]["bytes_written"] += count
+ self.writes[pid]["total_writes"] += 1
+ self.writes[pid]["comm"] = comm
+ except AttributeError:
+ self.unhandled[event_name] += 1
+ elif event_name in ("syscalls:sys_exit_write", "raw_syscalls:sys_exit_write"):
+ try:
+ ret = sample.ret
+ if ret <= 0:
+ self.writes[pid]["errors"][ret] += 1
+ except AttributeError:
+ self.unhandled[event_name] += 1
+ else:
+ self.unhandled[event_name] += 1
+
+ def print_totals(self) -> None:
+ """Print summary tables."""
+ print("read counts by pid:\n")
+ print(
+ f"{'pid':>6s} {'comm':<20s} {'# reads':>10s} "
+ f"{'bytes_requested':>15s} {'bytes_read':>10s}"
+ )
+ print(f"{'-'*6} {'-'*20} {'-'*10} {'-'*15} {'-'*10}")
+
+ for pid, data in sorted(self.reads.items(),
+ key=lambda kv: kv[1]["bytes_read"], reverse=True):
+ print(
+ f"{pid:6d} {data['comm']:<20s} {data['total_reads']:10d} "
+ f"{data['bytes_requested']:15d} {data['bytes_read']:10d}"
+ )
+
+ print("\nfailed reads by pid:\n")
+ print(f"{'pid':>6s} {'comm':<20s} {'error #':>6s} {'# errors':>10s}")
+ print(f"{'-'*6} {'-'*20} {'-'*6} {'-'*10}")
+
+ errcounts: List[Tuple[int, str, int, int]] = []
+ for pid, data in self.reads.items():
+ for error, count in data["errors"].items():
+ errcounts.append((pid, data["comm"], error, count))
+
+ for pid, comm, error, count in sorted(errcounts, key=lambda x: x[3], reverse=True):
+ print(f"{pid:6d} {comm:<20s} {error:6d} {count:10d}")
+
+ print("\nwrite counts by pid:\n")
+ print(f"{'pid':>6s} {'comm':<20s} {'# writes':>10s} {'bytes_written':>15s}")
+ print(f"{'-'*6} {'-'*20} {'-'*10} {'-'*15}")
+
+ for pid, data in sorted(self.writes.items(),
+ key=lambda kv: kv[1]["bytes_written"], reverse=True):
+ print(
+ f"{pid:6d} {data['comm']:<20s} "
+ f"{data['total_writes']:10d} {data['bytes_written']:15d}"
+ )
+
+ print("\nfailed writes by pid:\n")
+ print(f"{'pid':>6s} {'comm':<20s} {'error #':>6s} {'# errors':>10s}")
+ print(f"{'-'*6} {'-'*20} {'-'*6} {'-'*10}")
+
+ errcounts = []
+ for pid, data in self.writes.items():
+ for error, count in data["errors"].items():
+ errcounts.append((pid, data["comm"], error, count))
+
+ for pid, comm, error, count in sorted(errcounts, key=lambda x: x[3], reverse=True):
+ print(f"{pid:6d} {comm:<20s} {error:6d} {count:10d}")
+
+ if self.unhandled:
+ print("\nunhandled events:\n")
+ print(f"{'event':<40s} {'count':>10s}")
+ print(f"{'-'*40} {'-'*10}")
+ for event_name, count in self.unhandled.items():
+ print(f"{event_name:<40s} {count:10d}")
+
+ def run(self, input_file: str) -> None:
+ """Run the session."""
+ self.session = perf.session(perf.data(input_file), sample=self.process_event)
+ self.session.process_events()
+ self.print_totals()
+
+def main() -> None:
+ """Main function."""
+ parser = argparse.ArgumentParser(description="Trace r/w activity by PID")
+ parser.add_argument("-i", "--input", default="perf.data", help="Input file")
+ args = parser.parse_args()
+
+ analyzer = RwByPid()
+ try:
+ analyzer.run(args.input)
+ except IOError as e:
+ print(e, file=sys.stderr)
+ sys.exit(1)
+
+if __name__ == "__main__":
+ main()
--
2.54.0.545.g6539524ca2-goog