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Only use opened queue slots on running workers #7190

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de899fb
Only use opened queue slots on running workers
gjoseph92 Oct 25, 2022
3b9d127
add test
gjoseph92 Oct 28, 2022
29cf615
driveby: remove extraneous validation
gjoseph92 Oct 28, 2022
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9 changes: 5 additions & 4 deletions distributed/scheduler.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2167,10 +2167,7 @@ def decide_worker_rootish_queuing_enabled(self) -> WorkerState | None:
_task_slots_available(ws, self.WORKER_SATURATION),
)
assert ws in self.running, (ws, self.running)

if self.validate and ws is not None:
assert self.workers.get(ws.address) is ws
assert ws in self.running, (ws, self.running)

return ws

Expand Down Expand Up @@ -7878,7 +7875,11 @@ def _exit_processing_common(
state.release_resources(ts, ws)

# If a slot has opened up for a queued task, schedule it.
if state.queued and not _worker_full(ws, state.WORKER_SATURATION):
if (
state.queued
and ws.status == Status.running

@fjetter fjetter Oct 26, 2022

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This is true right now but if we ever had more Status types, of which some might actually be runnable, this could cause a deadlock, couldn't it?
I know this is pretty hypothetical but my point is that we do not change the behavior but encode more assumptions in the code for a perf improvement you call yourself minuscule (and rare)

I don't mean to block this if you consider it truly better readable but I'm a soft -0

@gjoseph92 gjoseph92 Oct 28, 2022

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That seems like a pretty far-fetched problem. There are already 18 instances of == Status.running in scheduler.py.

I've added a test. This is still not a big deal, it's just a small tidying up.

and not _worker_full(ws, state.WORKER_SATURATION)
):
qts = state.queued.peek()
if state.validate:
assert qts.state == "queued", qts.state
Expand Down
36 changes: 36 additions & 0 deletions distributed/tests/test_scheduler.py
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Expand Up @@ -408,6 +408,42 @@ async def test_queued_remove_add_worker(c, s, a, b):
await wait(fs)


@gen_cluster(
client=True,
nthreads=[("", 1)],
config={
"distributed.scheduler.worker-saturation": 1.0,
"distributed.worker.memory.pause": False,
"distributed.worker.memory.target": False,
"distributed.worker.memory.spill": False,
},
)
async def test_queued_dont_try_non_running_worker(c, s, a):
"When a slot opens on a non-running worker, don't consider scheduling a queued task"
events = [Event() for _ in range(5)]
fs = c.map(lambda ev: ev.wait(), events, key=[f"w-{i}" for i in range(len(events))])

await async_wait_for(lambda: s.queued, timeout=5)

a.status = Status.paused

await async_wait_for(lambda: not s.running, timeout=5)

assert len(a.state.executing) == 1
a_key: str = next(iter(a.state.executing)).key
a_task = s.tasks[a_key]
a_event = events[int(a_key[2])]

front_of_queue = s.queued.peek()

assert a_task.state == "processing"
await a_event.set()
await wait_for_state(a_key, "memory", s)

story = s.story(front_of_queue)
assert story[-1][1:2] != ["queued", "queued"], story


@pytest.mark.parametrize(
"saturation_config, expected_task_counts",
[
Expand Down