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Improve `reactor_tick_time` metric (#11724) 

The existing implementation of the `python_twisted_reactor_tick_time` metric is pretty useless, because it *only* 
measures the time taken to execute timed calls and callbacks from threads. That neglects everything that 
happens off the back of I/O, which is obviously quite a lot for us.

To improve this, I've hooked into a different place in the reactor - in particular, where it calls `epoll`. That call is 
the only place it should wait for something to happen - the rest of the loop *should* be quick.

I've also removed `python_twisted_reactor_pending_calls`, because I don't believe anyone ever looks at it, and
it's a nuisance to populate.
This commit is contained in:
Richard van der Hoff 2022-01-17 12:14:40 +00:00 committed by GitHub
parent 6b241f5286
commit 6a78ede569
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5 changed files with 86 additions and 109 deletions
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1
changelog.d/11724.misc Normal file
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@ -0,0 +1 @@
Improve accuracy of `python_twisted_reactor_tick_time` prometheus metric.

1
changelog.d/11724.removal Normal file
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@ -0,0 +1 @@
Remove `python_twisted_reactor_pending_calls` prometheus metric.

16
contrib/prometheus/consoles/synapse.html
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@ -92,22 +92,6 @@ new PromConsole.Graph({
})
</script>
<h3>Pending calls per tick</h3>
<div id="reactor_pending_calls"></div>
<script>
new PromConsole.Graph({
node: document.querySelector("#reactor_pending_calls"),
expr: "rate(python_twisted_reactor_pending_calls_sum[30s]) / rate(python_twisted_reactor_pending_calls_count[30s])",
name: "[[job]]-[[index]]",
min: 0,
renderer: "line",
height: 150,
yAxisFormatter: PromConsole.NumberFormatter.humanize,
yHoverFormatter: PromConsole.NumberFormatter.humanize,
yTitle: "Pending Calls"
})
</script>
<h1>Storage</h1>
<h3>Queries</h3>

94
synapse/metrics/__init__.py
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@ -12,15 +12,12 @@
# See the License for the specific language governing permissions and
# limitations under the License.
import functools
import itertools
import logging
import os
import platform
import threading
import time
from typing import (
Any,
Callable,
Dict,
Generic,
@ -33,7 +30,6 @@ from typing import (
Type,
TypeVar,
Union,
cast,
)
import attr
@ -44,11 +40,9 @@ from prometheus_client.core import (
GaugeMetricFamily,
)
from twisted.internet import reactor
from twisted.internet.base import ReactorBase
from twisted.python.threadpool import ThreadPool
import synapse
import synapse.metrics._reactor_metrics
from synapse.metrics._exposition import (
MetricsResource,
generate_latest,
@ -368,21 +362,6 @@ class CPUMetrics:
REGISTRY.register(CPUMetrics())
#
# Twisted reactor metrics
#
tick_time = Histogram(
"python_twisted_reactor_tick_time",
"Tick time of the Twisted reactor (sec)",
buckets=[0.001, 0.002, 0.005, 0.01, 0.025, 0.05, 0.1, 0.2, 0.5, 1, 2, 5],
)
pending_calls_metric = Histogram(
"python_twisted_reactor_pending_calls",
"Pending calls",
buckets=[1, 2, 5, 10, 25, 50, 100, 250, 500, 1000],
)
#
# Federation Metrics
#
@ -434,8 +413,6 @@ build_info.labels(
" ".join([platform.system(), platform.release()]),
).set(1)
last_ticked = time.time()
# 3PID send info
threepid_send_requests = Histogram(
"synapse_threepid_send_requests_with_tries",
@ -483,75 +460,6 @@ def register_threadpool(name: str, threadpool: ThreadPool) -> None:
)
class ReactorLastSeenMetric:
def collect(self) -> Iterable[Metric]:
cm = GaugeMetricFamily(
"python_twisted_reactor_last_seen",
"Seconds since the Twisted reactor was last seen",
)
cm.add_metric([], time.time() - last_ticked)
yield cm
REGISTRY.register(ReactorLastSeenMetric())
F = TypeVar("F", bound=Callable[..., Any])
def runUntilCurrentTimer(reactor: ReactorBase, func: F) -> F:
@functools.wraps(func)
def f(*args: Any, **kwargs: Any) -> Any:
now = reactor.seconds()
num_pending = 0
# _newTimedCalls is one long list of *all* pending calls. Below loop
# is based off of impl of reactor.runUntilCurrent
for delayed_call in reactor._newTimedCalls:
if delayed_call.time > now:
break
if delayed_call.delayed_time > 0:
continue
num_pending += 1
num_pending += len(reactor.threadCallQueue)
start = time.time()
ret = func(*args, **kwargs)
end = time.time()
# record the amount of wallclock time spent running pending calls.
# This is a proxy for the actual amount of time between reactor polls,
# since about 25% of time is actually spent running things triggered by
# I/O events, but that is harder to capture without rewriting half the
# reactor.
tick_time.observe(end - start)
pending_calls_metric.observe(num_pending)
# Update the time we last ticked, for the metric to test whether
# Synapse's reactor has frozen
global last_ticked
last_ticked = end
return ret
return cast(F, f)
try:
# Ensure the reactor has all the attributes we expect
reactor.seconds # type: ignore
reactor.runUntilCurrent # type: ignore
reactor._newTimedCalls # type: ignore
reactor.threadCallQueue # type: ignore
# runUntilCurrent is called when we have pending calls. It is called once
# per iteratation after fd polling.
reactor.runUntilCurrent = runUntilCurrentTimer(reactor, reactor.runUntilCurrent) # type: ignore
except AttributeError:
pass
__all__ = [
"MetricsResource",
"generate_latest",

83
synapse/metrics/_reactor_metrics.py Normal file
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@ -0,0 +1,83 @@
# Copyright 2022 The Matrix.org Foundation C.I.C.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
import select
import time
from typing import Any, Iterable, List, Tuple
from prometheus_client import Histogram, Metric
from prometheus_client.core import REGISTRY, GaugeMetricFamily
from twisted.internet import reactor
#
# Twisted reactor metrics
#
tick_time = Histogram(
"python_twisted_reactor_tick_time",
"Tick time of the Twisted reactor (sec)",
buckets=[0.001, 0.002, 0.005, 0.01, 0.025, 0.05, 0.1, 0.2, 0.5, 1, 2, 5],
)
class EpollWrapper:
"""a wrapper for an epoll object which records the time between polls"""
def __init__(self, poller: "select.epoll"):
self.last_polled = time.time()
self._poller = poller
def poll(self, *args, **kwargs) -> List[Tuple[int, int]]: # type: ignore[no-untyped-def]
# record the time since poll() was last called. This gives a good proxy for
# how long it takes to run everything in the reactor - ie, how long anything
# waiting for the next tick will have to wait.
tick_time.observe(time.time() - self.last_polled)
ret = self._poller.poll(*args, **kwargs)
self.last_polled = time.time()
return ret
def __getattr__(self, item: str) -> Any:
return getattr(self._poller, item)
class ReactorLastSeenMetric:
def __init__(self, epoll_wrapper: EpollWrapper):
self._epoll_wrapper = epoll_wrapper
def collect(self) -> Iterable[Metric]:
cm = GaugeMetricFamily(
"python_twisted_reactor_last_seen",
"Seconds since the Twisted reactor was last seen",
)
cm.add_metric([], time.time() - self._epoll_wrapper.last_polled)
yield cm
try:
# if the reactor has a `_poller` attribute, which is an `epoll` object
# (ie, it's an EPollReactor), we wrap the `epoll` with a thing that will
# measure the time between ticks
from select import epoll
poller = reactor._poller # type: ignore[attr-defined]
except (AttributeError, ImportError):
pass
else:
if isinstance(poller, epoll):
poller = EpollWrapper(poller)
reactor._poller = poller # type: ignore[attr-defined]
REGISTRY.register(ReactorLastSeenMetric(poller))