* Bound how many approvals may park, against the executor
#7455 landed parking, which is the right shape and supersedes what this branch
was carrying. It is unbounded, though, and the thing it is unbounded against is
not the GPU.
A run stopped on an approval prompt is blocked inside the to_thread(next, gen)
call that drives it, so it holds one of asyncio's default min(32, cpu + 4)
executor threads until the user answers. The slot cap used to bound that.
Parking hands the slot back, which admits another run that can park too, so the
ceiling became the wait line: 64 deep on a 1-slot backend. Long before that, the
executor is full and nothing else in the backend runs, including generation
steps for chats that already hold slots and the stream teardown that would clean
up after a disconnect.
The pool already permits `capacity` pending prompts, and each park adds one
more, so the budget is what the executor has left after the cap and a reserve of
4. On this machine (32 workers) --parallel 4 gets 8 parks and 20 free threads,
--parallel 24 gets 4 and 4, and --parallel 28 or higher gets none: there the
prompt keeps its slot and behaves exactly as it did before parking existed.
Counted process-wide rather than per queue. There is one executor, but a
per-queue budget is the same allowance again for every backend, and base_url
carries a fresh port on every model load, so a reload would mint a queue that
knows nothing about the approvals still parked on the old one. A reset clears it
too, or a leaked claim shrinks the budget for the life of the process.
park() reports whether it took the budget, and a refusal costs nothing to undo
because the slot never left its holder. The stream reads that answer rather than
recording a refused park as parked, which would make it skip the park for every
later approval in the same run even once the budget freed up.
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* Size the park budget from the executor's own CPU count
Two review findings, both real.
The budget read os.cpu_count(). 3.13 sizes ThreadPoolExecutor from
os.process_cpu_count(), which honours CPU affinity and cgroup quotas, and
asyncio's default executor is a plain ThreadPoolExecutor(), so a container
pinned to one core on a 64-core host got a 5-thread executor and a budget
computed from 64. The bound was then looser than no bound at all in exactly the
environment that can least afford it. It asks the same source the executor does,
and the test compares against a real ThreadPoolExecutor rather than restating
the formula, so it stays right on 3.12 as well.
The reserve was a flat 4, which on that same 5-thread executor left nothing to
budget and turned parking off entirely. Small hosts are where a chat most needs
to keep moving while another sits on a prompt. It scales now, and the ceiling
has a floor of two: a quarter of five is one, and one park cannot cover two
chats on prompts at once, which is what #7455's own two-approvals test needs.
Without that floor, that test fails on a one or two CPU runner. `spare` still
takes the budget to zero when the pool already fills the executor, so nothing
about a 32-worker machine changes: --parallel 4 still gets 8 parks, 24 gets 4,
28 gets none.
The two behavioural budget tests pin the worker count rather than reading it off
the runner, and the property test sweeps executor sizes from one CPU to 64
instead of asserting against whatever the host happens to have. The whole suite
passes with the CPU count faked to 1, 2 and 4, which is how both of these were
reproduced.
* [pre-commit.ci] auto fixes from pre-commit.com hooks
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* Size the park budget from every live backend, and free it on the answer
Two review findings, both real.
The budget was global but sized from one queue's capacity. A reload mints a
queue on a new port while the old one drains, so both are live, and prompts on
both park executor threads. Eight parks on an old 1-slot queue plus a new
24-slot backend is 32 threads on a 32-thread executor, with the new backend's
prompts refused and holding their slots, which is the state the reserve exists
to prevent. It sums the capacity of every backend still serving instead. Idle
queues are skipped: those are the ones the registry is about to evict, and they
are holding nothing.
The budget also outlived the wait it was paying for. unpark_async only dropped
it after reacquiring a slot, but the generator yields its post-approval event
first, so the executor thread is already back in the pool while the resume
queues. An approved chat waiting on a slot would refuse a different chat's park,
and that chat then keeps the slot the resumer is waiting for, so an unanswered
prompt strands chats that were already approved. The budget is released when the
prompt wait ends now, and the queue's parked count still runs until the slot is
back, which is what guards idle eviction and the resume ordering.
Both are separate counters on the lease as a result, and every exit from a park
drops the budget: unpark, unpark_async and release. That last one was the mutant
that came back missed, since a client disconnecting on a prompt releases
straight out of parked and would otherwise lose a budget slot for good.
* [pre-commit.ci] auto fixes from pre-commit.com hooks
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* Tighten the comments on the park budget
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Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
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