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Differential D4342

contrib: new script to read events from a named pipe and emit catapult traces
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Authored by durin42 on Aug 21 2018, 5:39 PM.

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rHG9a81f126f9fa: contrib: new script to read events from a named pipe and emit catapult traces
Summary

I'm starting to get more serious about getting some insight into where
we're spending our time, both in hg itself but also in the test
suite. As a first pass, I'm going to try and produce catapult
traces[0] that can be viewed with Chrome's about:tracing tool.

0: https://docs.google.com/document/d/1CvAClvFfyA5R-PhYUmn5OOQtYMH4h6I0nSsKchNAySU/edit#heading=h.nso4gcezn7n1

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Event Timeline

durin42 created this revision.Aug 21 2018, 5:39 PM
durin42 added a comment.Aug 21 2018, 5:42 PM

This series is RFC-ish: I'd very much like to land it (and find additional things we could have emit events!), but I also am not really in love with any of the names involved.

It looks like it'll be useful to debug some slowness problems at Google, at the very least.

indygreg added a subscriber: indygreg.Aug 21 2018, 6:50 PM

Overall this series seems pretty reasonably and exciting! You say it is RFC-ish. But aside from the possibly-too-early import in hg, I'm tempted to queue this.

durin42 added a comment.Aug 21 2018, 7:26 PM
In D4342#66808, @indygreg wrote:

Overall this series seems pretty reasonably and exciting! You say it is RFC-ish. But aside from the possibly-too-early import in hg, I'm tempted to queue this.

That's honestly fine with me, with the addendum that the script-level trace event is pretty critical, because otherwise we can't identify _anything_ that happens before dispatch.run(), and that turns out to be a fair amount.

durin42 added a comment.Aug 21 2018, 7:27 PM
In D4342#66810, @durin42 wrote:
In D4342#66808, @indygreg wrote:

Overall this series seems pretty reasonably and exciting! You say it is RFC-ish. But aside from the possibly-too-early import in hg, I'm tempted to queue this.

That's honestly fine with me, with the addendum that the script-level trace event is pretty critical, because otherwise we can't identify _anything_ that happens before dispatch.run(), and that turns out to be a fair amount.

Oh, and I'm really not in love with the catapipe.py name - got any suggestions for something better?

indygreg added a comment.Aug 24 2018, 12:59 PM
In D4342#66811, @durin42 wrote:

Oh, and I'm really not in love with the catapipe.py name - got any suggestions for something better?

Nothing definitive. But since this is related to tracing, maybe have tracing in the name?

I'm a bit worried about using wall clocks computed from the trace reader here. But none of this has BC concerns, so we could change that.

I'll look at the remainder of the series and considering queuing this. Perfect is very much the enemy of done here.

contrib/catapipe.py
58–60

This is taking the start time before the readline(). So, the time will be misreported if it takes a while for an event to arrive.

My experience with profiling is that attempting to measure time when buffers (like pipes) are involved will result in various data misrepresentation. I find it best to record times in the producer and propagate those to consumers. Of course, this introduces a system call in the producer to get the current time, which adds overhead.

63

Do we need to use wall time here? A monotonic timer would be preferred for computing deltas. The best we have in Python 2 is time.clock(). If we use Python 3, we could use time.perf_counter().

Closed by commit rHG9a81f126f9fa: contrib: new script to read events from a named pipe and emit catapult traces (authored by durin42). · Explain WhyAug 24 2018, 1:14 PM
This revision was automatically updated to reflect the committed changes.
durin42 added a comment.Aug 28 2018, 1:53 PM

This is taking the start time before the readline(). So, the time will be misreported if it takes a while for an event to arrive.

Gloriously, this doesn’t actually matter! As long as we have a fixed reference time for the entire event stream it isn’t a big deal, and the trace viewer makes that easy enough to understand.

Revision Contents
Changeset List

PathPackages
AMcontrib/catapipe.py (85 lines)

Diff 10551

contrib/catapipe.py

  • This file was added.
#!/usr/bin/env python3
#
# Copyright 2018 Google LLC.
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.
"""Tool read primitive events from a pipe to produce a catapult trace.
For now the event stream supports
START $SESSIONID ...
and
END $SESSIONID ...
events. Everything after the SESSIONID (which must not contain spaces)
is used as a label for the event. Events are timestamped as of when
they arrive in this process and are then used to produce catapult
traces that can be loaded in Chrome's about:tracing utility. It's
important that the event stream *into* this process stay simple,
because we have to emit it from the shell scripts produced by
run-tests.py.
Typically you'll want to place the path to the named pipe in the
HGCATAPULTSERVERPIPE environment variable, which both run-tests and hg
understand.
"""
from __future__ import absolute_import, print_function
import argparse
import datetime
import json
import os
_TYPEMAP = {
'START': 'B',
'END': 'E',
}
_threadmap = {}
def main():
parser = argparse.ArgumentParser()
parser.add_argument('pipe', type=str, nargs=1,
help='Path of named pipe to create and listen on.')
parser.add_argument('output', default='trace.json', type=str, nargs='?',
help='Path of named pipe to create and listen on.')
parser.add_argument('--debug', default=False, action='store_true',
help='Print useful debug messages')
args = parser.parse_args()
fn = args.pipe[0]
os.mkfifo(fn)
try:
with open(fn) as f, open(args.output, 'w') as out:
out.write('[\n')
start = datetime.datetime.now()
while True:
ev = f.readline().strip()
if not ev:
indygregUnsubmitted
Not Done

This is taking the start time before the readline(). So, the time will be misreported if it takes a while for an event to arrive.

My experience with profiling is that attempting to measure time when buffers (like pipes) are involved will result in various data misrepresentation. I find it best to record times in the producer and propagate those to consumers. Of course, this introduces a system call in the producer to get the current time, which adds overhead.

indygreg: This is taking the start time before the `readline()`. So, the time will be misreported if it…
continue
now = datetime.datetime.now()
if args.debug:
indygregUnsubmitted
Not Done

Do we need to use wall time here? A monotonic timer would be preferred for computing deltas. The best we have in Python 2 is time.clock(). If we use Python 3, we could use time.perf_counter().

indygreg: Do we need to use wall time here? A monotonic timer would be preferred for computing deltas.
print(ev)
verb, session, label = ev.split(' ', 2)
if session not in _threadmap:
_threadmap[session] = len(_threadmap)
pid = _threadmap[session]
ts_micros = (now - start).total_seconds() * 1000000
out.write(json.dumps(
{
"name": label,
"cat": "misc",
"ph": _TYPEMAP[verb],
"ts": ts_micros,
"pid": pid,
"tid": 1,
"args": {}
}))
out.write(',\n')
finally:
os.unlink(fn)
if __name__ == '__main__':
main()