test_close_at_bad_time_for_send_all failure on PPC

Since at least 0.16.0, this failure only occurs on PPC for openSUSE builds at
https://build.opensuse.org/package/show/devel:languages:python/python-trio

trio/tests/test_unix_pipes.py::test_close_at_bad_time_for_send_all Timeout (0:01:00)!
Thread 0x00007fffab7ef0f0 (most recent call first):
  File "/home/abuild/rpmbuild/BUILD/trio-0.16.0/trio/_core/tests/test_thread_cache.py", line 102 in acquire
  File "/home/abuild/rpmbuild/BUILD/trio-0.16.0/trio/_core/_thread_cache.py", line 62 in _work
  File "/usr/lib64/python3.8/threading.py", line 870 in run
  File "/usr/lib64/python3.8/threading.py", line 932 in _bootstrap_inner
  File "/usr/lib64/python3.8/threading.py", line 890 in _bootstrap

Thread 0x00007fffbdeb4ea0 (most recent call first):
  File "/home/abuild/rpmbuild/BUILD/trio-0.16.0/trio/_core/_io_epoll.py", line 223 in get_events
  File "/home/abuild/rpmbuild/BUILD/trio-0.16.0/trio/_core/_run.py", line 1890 in run
  File "/home/abuild/rpmbuild/BUILD/trio-0.16.0/trio/testing/_trio_test.py", line 27 in wrapper
  File "/usr/lib/python3.8/site-packages/_pytest/python.py", line 180 in pytest_pyfunc_call
  File "/usr/lib/python3.8/site-packages/pluggy/callers.py", line 187 in _multicall
  File "/usr/lib/python3.8/site-packages/pluggy/manager.py", line 84 in <lambda>
  File "/usr/lib/python3.8/site-packages/pluggy/manager.py", line 93 in _hookexec
  File "/usr/lib/python3.8/site-packages/pluggy/hooks.py", line 286 in __call__
  File "/usr/lib/python3.8/site-packages/_pytest/python.py", line 1567 in runtest
  File "/usr/lib/python3.8/site-packages/_pytest/runner.py", line 153 in pytest_runtest_call
  File "/usr/lib/python3.8/site-packages/pluggy/callers.py", line 187 in _multicall
  File "/usr/lib/python3.8/site-packages/pluggy/manager.py", line 84 in <lambda>
  File "/usr/lib/python3.8/site-packages/pluggy/manager.py", line 93 in _hookexec
  File "/usr/lib/python3.8/site-packages/pluggy/hooks.py", line 286 in __call__
  File "/usr/lib/python3.8/site-packages/_pytest/runner.py", line 247 in <lambda>
  File "/usr/lib/python3.8/site-packages/_pytest/runner.py", line 294 in from_call
  File "/usr/lib/python3.8/site-packages/_pytest/runner.py", line 246 in call_runtest_hook
  File "/usr/lib/python3.8/site-packages/_pytest/runner.py", line 207 in call_and_report
  File "/usr/lib/python3.8/site-packages/_pytest/runner.py", line 117 in runtestprotocol
  File "/usr/lib/python3.8/site-packages/_pytest/runner.py", line 100 in pytest_runtest_protocol
  File "/usr/lib/python3.8/site-packages/pluggy/callers.py", line 187 in _multicall
  File "/usr/lib/python3.8/site-packages/pluggy/manager.py", line 84 in <lambda>
  File "/usr/lib/python3.8/site-packages/pluggy/manager.py", line 93 in _hookexec
  File "/usr/lib/python3.8/site-packages/pluggy/hooks.py", line 286 in __call__
  File "/usr/lib/python3.8/site-packages/_pytest/main.py", line 321 in pytest_runtestloop
  File "/usr/lib/python3.8/site-packages/pluggy/callers.py", line 187 in _multicall
  File "/usr/lib/python3.8/site-packages/pluggy/manager.py", line 84 in <lambda>
  File "/usr/lib/python3.8/site-packages/pluggy/manager.py", line 93 in _hookexec
  File "/usr/lib/python3.8/site-packages/pluggy/hooks.py", line 286 in __call__
  File "/usr/lib/python3.8/site-packages/_pytest/main.py", line 296 in _main
  File "/usr/lib/python3.8/site-packages/_pytest/main.py", line 240 in wrap_session
  File "/usr/lib/python3.8/site-packages/_pytest/main.py", line 289 in pytest_cmdline_main
  File "/usr/lib/python3.8/site-packages/pluggy/callers.py", line 187 in _multicall
  File "/usr/lib/python3.8/site-packages/pluggy/manager.py", line 84 in <lambda>
  File "/usr/lib/python3.8/site-packages/pluggy/manager.py", line 93 in _hookexec
  File "/usr/lib/python3.8/site-packages/pluggy/hooks.py", line 286 in __call__
  File "/usr/lib/python3.8/site-packages/_pytest/config/__init__.py", line 157 in main
  File "/usr/lib/python3.8/site-packages/_pytest/config/__init__.py", line 180 in console_main
  File "/usr/bin/pytest-3.8", line 11 in <module>


Job seems to be stuck here, killed. (after 12000 seconds of inactivity)

Any hints greatly appreciated.

Start with trio/tests/test_unix_pipes.py::test_close_at_bad_time_for_send_all and reproduce the timeout on PPC openSUSE. Read the stack-traced paths in trio/_core/_io_epoll.py, trio/_core/_run.py, and trio/_core/_thread_cache.py, especially get_events, _work, and acquire. Done means identifying the platform-specific cause and making the test complete without timing out.