mirror of
https://github.com/element-hq/synapse.git
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126 lines
4.7 KiB
Python
126 lines
4.7 KiB
Python
#
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# This file is licensed under the Affero General Public License (AGPL) version 3.
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#
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# Copyright (C) 2026 Element Creations Ltd
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#
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# This program is free software: you can redistribute it and/or modify
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# it under the terms of the GNU Affero General Public License as
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# published by the Free Software Foundation, either version 3 of the
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# License, or (at your option) any later version.
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#
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# See the GNU Affero General Public License for more details:
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# <https://www.gnu.org/licenses/agpl-3.0.html>.
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#
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import os
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import threading
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import time
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from synapse.metrics.thread_cpu import ThreadCPUMetrics
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from synapse.util.duration import Duration
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from tests import unittest
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# How much CPU time to burn on each thread, in seconds.
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BURN = Duration(milliseconds=200)
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# How far a thread's reported CPU may fall short of its burn. The kernel
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# reports CPU time in whole ticks, rounded down.
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TOLERANCE = Duration(milliseconds=50)
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def _burn_cpu() -> None:
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"""Spin on the calling thread until it has used `BURN_SECONDS` of CPU."""
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start = time.thread_time()
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while time.thread_time() - start < BURN.as_secs():
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pass
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def _collect(metrics: ThreadCPUMetrics) -> dict[str, float]:
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"""Scrape `metrics` and map each thread type to its CPU seconds.
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User and system time are summed. The kernel splits a thread's CPU time
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between the two by sampling, so a burn in user code can show up partly as
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system time.
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"""
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totals: dict[str, float] = {}
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for metric in metrics.collect():
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for sample in metric.samples:
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if sample.name == "synapse_thread_cpu_seconds_total":
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thread_type = sample.labels["thread_type"]
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totals[thread_type] = totals.get(thread_type, 0.0) + sample.value
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return totals
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class ThreadCPUMetricsTestCase(unittest.TestCase):
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def test_cpu_adds_up(self) -> None:
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"""CPU used between two scrapes is reported under the right thread
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type, and the types add up to the CPU the whole process used.
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"""
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if not os.path.isdir("/proc/self/task"):
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self.skipTest(
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"Skipping as `ThreadCPUMetrics` tests require /proc/self/task (Linux only)"
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)
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# A fresh collector, so threads registered elsewhere don't count. It
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# reports process-level metrics, so it has no `SERVER_NAME_LABEL`.
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metrics = ThreadCPUMetrics() # type: ignore[missing-server-name-label]
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# First record the base CPU metrics.
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before = _collect(metrics)
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process_before = sum(os.times()[:2])
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# First we setup and burn some CPU on a separate thread.
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# The collector only sees live threads, so the thread waits for
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# `release` until after the second scrape.
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burnt = threading.Event()
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release = threading.Event()
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def run_on_thread() -> None:
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_burn_cpu()
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burnt.set()
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release.wait(timeout=Duration(seconds=10).as_secs())
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# Since `/proc/<tid>/stat` puts the thread name in brackets and uses
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# spaces as field separators, choose a thread name with those characters
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# to ensure we parse it correctly.
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#
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# Note that the thread name only gets passed to the kernel from Python
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# 3.14 onwards.
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thread = threading.Thread(target=run_on_thread, name="a) b) (c")
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thread.start()
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self.addCleanup(thread.join)
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self.addCleanup(release.set)
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metrics.register_thread("test-thread", thread)
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# Wait for the separate thread to burn CPU before continuing.
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self.assertTrue(burnt.wait(timeout=Duration(seconds=10).as_secs()))
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# Next burn some CPU on the main thread.
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_burn_cpu()
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# Now collect the CPU metrics after burning on both threads.
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after = _collect(metrics)
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process_delta = sum(os.times()[:2]) - process_before
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# Check that each thread burned at least the expected amount of CPU.
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def delta(thread_type: str) -> Duration:
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secs = after[thread_type] - before.get(thread_type, 0.0)
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return Duration(seconds=secs)
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threads_delta = sum(after.values()) - sum(before.values())
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self.assertGreaterEqual(delta("main"), BURN - TOLERANCE)
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self.assertGreaterEqual(delta("test-thread"), BURN - TOLERANCE)
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# Check that the sum of the per-thread CPU deltas is (more-or-less) the
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# same as the whole process CPU delta.
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# The sum over threads can lag the process total by up to a tick per
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# thread. Allow a couple more ticks for the scrapes themselves.
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tick = 1 / os.sysconf("SC_CLK_TCK")
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slack = (len(os.listdir("/proc/self/task")) + 2) * tick
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self.assertLessEqual(abs(threads_delta - process_delta), slack)
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