[PATCH v8 50/58] perf rwtop: Port rwtop to use python module

Ian Rogers
2026-04-28T07:20:59Z

Port the legacy Perl script rwtop.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 periodically displays system-wide r/w call activity, broken down by
PID, refreshed every interval.

Complications:
- Implemented periodic display based on event timestamps
(sample.sample_time) instead of relying on SIGALRM, making it robust
for file-based processing.
- Used ANSI escape codes (\x1b[H\x1b[2J) to clear the terminal.
- Fixed unused imports and indentation issues identified by pylint.
- 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:

- Added Live Session Support: Updated main() to start a LiveSession
when the input file does not exist (or is the default "perf.data"
and doesn't exist). It traces read and write entry/exit
tracepoints.

- Fixed Live Mode Comm Resolution: Fixed a bug in process_event()
where it would attempt to use self.session to resolve the command
name when running in live mode (where self.session is None ). It
now falls back to f"PID({pid})" when in live mode or if resolution
fails.

- Fixed Substring Matching: Replaced loose substring checks like if
"sys_enter_read" in event_name: with exact matches against
"evsel(syscalls:sys_enter_read)" and
"evsel(raw_syscalls:sys_enter_read)" using str(sample.evsel) . This
prevents unrelated syscalls with similar names (like readv or
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() . Now, if a sample lacks
expected fields, it is added to the self.unhandled tracker instead
of being silently ignored.

- Fixed Write Byte Counting: Updated the write exit handler to use
sample.ret to count actual bytes written on success, and tracked
requested bytes separately in the enter handler, matching the read
behavior.

- Added Error Tables to Output: Added tables to display failed reads
and writes by PID in print_totals() , which were previously tracked
but never displayed.

- Fixed Offline Output (Ghosting): Removed the hardcoded ANSI
clear-screen escape codes in print_totals() , as they corrupted
output when processing offline trace files at CPU speed or when
piping the output.

- Code Cleanup: Fixed a bug where fd was printed instead of pid in
the read counts table, and broke long lines to satisfy pylint.
---
tools/perf/python/rwtop.py | 219 +++++++++++++++++++++++++++++++++++++
1 file changed, 219 insertions(+)
create mode 100755 tools/perf/python/rwtop.py

diff --git a/tools/perf/python/rwtop.py b/tools/perf/python/rwtop.py
new file mode 100755
index 000000000000..895ebab9af10
--- /dev/null
+++ b/tools/perf/python/rwtop.py
@@ -0,0 +1,219 @@
+#!/usr/bin/env python3
+# SPDX-License-Identifier: GPL-2.0-only
+"""Periodically displays system-wide r/w call activity, broken down by pid."""
+
+import argparse
+from collections import defaultdict
+import os
+import sys
+from typing import Optional, Dict, Any
+import perf
+from perf_live import LiveSession
+
+class RwTop:
+ """Periodically displays system-wide r/w call activity."""
+ def __init__(self, interval: int = 3, nlines: int = 20) -> None:
+ self.interval_ns = interval * 1000000000
+ self.nlines = nlines
+ 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_requested": 0,
+ "bytes_written": 0,
+ "total_writes": 0,
+ "comm": "",
+ "errors": defaultdict(int),
+ }
+ )
+ self.unhandled: Dict[str, int] = defaultdict(int)
+ self.session: Optional[perf.session] = None
+ self.last_print_time: int = 0
+
+ def process_event(self, sample: perf.sample_event) -> None: # pylint: disable=too-many-branches
+ """Process events."""
+ event_name = str(sample.evsel)
+ pid = sample.sample_pid
+ sample_time = sample.sample_time
+
+ if self.last_print_time == 0:
+ self.last_print_time = sample_time
+
+ # Check if interval has passed
+ if sample_time - self.last_print_time >= self.interval_ns:
+ self.print_totals()
+ self.last_print_time = sample_time
+
+ try:
+ comm = f"PID({pid})" if not self.session else self.session.find_thread(pid).comm()
+ except Exception: # pylint: disable=broad-except
+ comm = f"PID({pid})"
+
+ if event_name in ("evsel(syscalls:sys_enter_read)", "evsel(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 ("evsel(syscalls:sys_exit_read)", "evsel(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 ("evsel(syscalls:sys_enter_write)",
+ "evsel(raw_syscalls:sys_enter_write)"):
+ try:
+ count = sample.count
+ self.writes[pid]["bytes_requested"] += count
+ self.writes[pid]["total_writes"] += 1
+ self.writes[pid]["comm"] = comm
+ except AttributeError:
+ self.unhandled[event_name] += 1
+ elif event_name in ("evsel(syscalls:sys_exit_write)", "evsel(raw_syscalls:sys_exit_write)"):
+ try:
+ ret = sample.ret
+ if ret > 0:
+ self.writes[pid]["bytes_written"] += ret
+ else:
+ 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_req':>10s} {'bytes_read':>10s}"
+ )
+ print(f"{'-'*6} {'-'*20} {'-'*10} {'-'*10} {'-'*10}")
+
+ count = 0
+ 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']:10d} {data['bytes_read']:10d}"
+ )
+ count += 1
+ if count >= self.nlines:
+ break
+
+ print("\nfailed reads 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.reads.items():
+ for error, cnt in data["errors"].items():
+ errcounts.append((pid, data["comm"], error, cnt))
+
+ sorted_errcounts = sorted(errcounts, key=lambda x: x[3], reverse=True)
+ for pid, comm, error, cnt in sorted_errcounts[:self.nlines]:
+ print(f"{pid:6d} {comm:<20s} {error:6d} {cnt:10d}")
+
+ print("\nwrite counts by pid:\n")
+ print(
+ f"{'pid':>6s} {'comm':<20s} {'# writes':>10s} "
+ f"{'bytes_req':>10s} {'bytes_written':>13s}"
+ )
+ print(f"{'-'*6} {'-'*20} {'-'*10} {'-'*10} {'-'*13}")
+
+ count = 0
+ for pid, data in sorted(self.writes.items(),
+ key=lambda kv: kv[1]["bytes_written"], reverse=True):
+ print(
+ f"{pid:6d} {data['comm']:<20s} {data['total_writes']:10d} "
+ f"{data['bytes_requested']:10d} {data['bytes_written']:13d}"
+ )
+ count += 1
+ if count >= self.nlines:
+ break
+
+ 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, cnt in data["errors"].items():
+ errcounts.append((pid, data["comm"], error, cnt))
+
+ sorted_errcounts = sorted(errcounts, key=lambda x: x[3], reverse=True)
+ for pid, comm, error, cnt in sorted_errcounts[:self.nlines]:
+ print(f"{pid:6d} {comm:<20s} {error:6d} {cnt:10d}")
+
+ # Reset counts
+ self.reads.clear()
+ self.writes.clear()
+
+ 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()
+
+ # Print final totals if there are any left
+ if self.reads or self.writes:
+ self.print_totals()
+
+ 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 main() -> None:
+ """Main function."""
+ parser = argparse.ArgumentParser(description="Trace r/w activity by PID")
+ parser.add_argument(
+ "interval", type=int, nargs="?", default=3, help="Refresh interval in seconds"
+ )
+ parser.add_argument("-i", "--input", default="perf.data", help="Input file")
+ args = parser.parse_args()
+
+ analyzer = RwTop(args.interval)
+ try:
+ if not os.path.exists(args.input) and args.input == "perf.data":
+ # Live mode
+ events = (
+ "syscalls:sys_enter_read,syscalls:sys_exit_read,"
+ "syscalls:sys_enter_write,syscalls:sys_exit_write"
+ )
+ try:
+ live_session = LiveSession(events, sample_callback=analyzer.process_event)
+ except OSError:
+ events = (
+ "raw_syscalls:sys_enter_read,raw_syscalls:sys_exit_read,"
+ "raw_syscalls:sys_enter_write,raw_syscalls:sys_exit_write"
+ )
+ live_session = LiveSession(events, sample_callback=analyzer.process_event)
+ print("Live mode started. Press Ctrl+C to stop.", file=sys.stderr)
+ live_session.run()
+ else:
+ analyzer.run(args.input)
+ except IOError as e:
+ print(e, file=sys.stderr)
+ sys.exit(1)
+ except KeyboardInterrupt:
+ print("\nStopping live mode...", file=sys.stderr)
+ if analyzer.reads or analyzer.writes:
+ analyzer.print_totals()
+
+if __name__ == "__main__":
+ main()
--
2.54.0.545.g6539524ca2-goog