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[Test] Conformance suite for cache_salt across OpenAI entrypoints - #55886
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Taking the cc as an invitation to be thorough, so I read this against the RFC thread as well as the diff. Short version, the suite delivers the entrypoint half of the split, the file enforces the discipline the thread converged on rather than describing it, and my inline comments are one real gap plus two optional hardenings.
On coverage, two of the twelve rows from the thread live on the entrypoint axis. The strict xfail pins #47696, and your A/B table, salt lost with the flag on even though chunking never triggers, states the bug more sharply than the issue does. #51818 you defer with the reason stated, its failure is a continuation across engine requests, and another endpoint arm would not reach it. The remaining ten are tier rows on the other half of the split. One wording correction for the table in the description though. #51748 is not covered by #53769 in the executed sense. HF3FSKVConnector sits in that suite's exempt map as a declared rederiver with an evidence pointer, because CI cannot import the hf3fs client. A declared and gated claim is worth having, but nothing in-tree executes that path today, and the table reads as if an arm runs somewhere.
Your encoding constraint survives inspection. The module imports nothing from the hashing internals and asserts only on counter deltas, and the metrics regex accepts both the prometheus_client _total suffix and the per-engine labels, which is how loggers.py emits vllm:prefix_cache_hits. That counter counts tokens, so a zero delta is zero reused tokens. Positive controls are real controls here, and the story of the omitted-salt arm passing against a no-prefix-caching server until you added its control deserves the record, the RFC's predicted failure mode caught inside the file arguing for the RFC.
The split with #53769 is clean. File sets are disjoint, neither module imports the other, and dimensions.py stays theirs, so merge order is free, and unifying after both merge is the right sequencing.
On CI, the Part 1 entrypoints job collects this file and runs plain pytest over entrypoints/openai with the subdirectories ignored. The module runs serially in CI as a result, which matches the docstring's no-xdist requirement. I could not run the suite here, no GPU and no CPU build of this tree on my machine, so the pass counts are yours, but the file compiles, the repo ruff and format checks pass on it, and every flag it passes exists on this branch, including the pooler-config enable_chunked_processing field and the runner and convert pair.
| # rather than the unsalted path failing to cache at all. | ||
| before = _read_hits(server) | ||
| _post(server, "v1/completions", _completions_body(prompt_ids, None)) | ||
| _assert_reuse(_read_hits(server) - before, "completions, both unsalted") |
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Omission is covered here, and the empty string is a third state, live on one endpoint family. Completions, chat, responses, anthropic and the scale-out protocol all pin min_length=1 on cache_salt. The pooling base protocol does not, and the extra-key construction in kv_cache_utils.py checks truthiness rather than is not None, so an empty-string salt on /v1/embeddings returns 200 and shares the unsalted namespace. A tenant whose client emits an empty salt by mistake silently shares blocks with every unsalted request, which is this suite's bug class arriving through the front door. Worth either a pooling arm pinning the empty-string behavior, or better, a one-line min_length=1 on the pooling base protocol as a sibling change with an arm asserting the 422 to match the other endpoints. Pinning current behavior would pin the footgun, so I would take the second.
| #44706, #51899, #52655 and #43789, each of which changes that encoding. | ||
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| The counters are process-global, so these tests must run sequentially | ||
| against their own server. Do not run this module under pytest-xdist. |
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CI honors this today because the Part 1 job runs the directory with plain pytest, but nothing enforces it if that job ever grows -n or someone runs the module under xdist locally. A module-scoped autouse fixture asserting PYTEST_XDIST_WORKER is absent from the environment would turn this sentence into a failure instead of a hope. Optional.
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| @pytest.fixture(scope="module") | ||
| def chunked_pooling_server(): |
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These two fixtures differ only in the pooler-config JSON. A small helper taking a chunked flag and building the arg list would keep the A/B pair from drifting when someone later tunes one of them. Optional, the duplication reads fine as written.
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Thanks for taking the fix route in #56199 and for the credit. The autouse guard is what I had in mind, and the squash left everything else as reviewed. One correction on the new empty salt arm before it can do its job. The assert expects 422 but the server returns 400. FastAPI only sends its default 422 when nothing intercepts it, and vLLM does intercept it, |
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Diffed 12ba68f7 against the aeaf89ae head I reviewed, and the squash adds 52 lines and changes nothing else. The autouse guard is in and turns an xdist run into a failure instead of a silent mis-measurement, and the empty-salt arm now asserts the 400 the validation handler returns, with the reasoning written into the docstring and the comment. The strict xfail can do its job, it holds while #56199 sits open and forces the flip to a plain passing arm after a rebase over the fix. Nothing from my earlier comments is left open, so approving at 12ba68f7.
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Diffed 12ba68f7 against the aeaf89ae head I reviewed, and the squash adds 52 lines and changes nothing else. The autouse guard is in and turns an xdist run into a failure instead of a silent mis-measurement, and the empty-salt arm now asserts the 400 the validation handler returns, with the reasoning written into the docstring and the comment. The strict xfail can do its job, it holds while #56199 sits open and forces the flip to a plain passing arm after a rebase over the fix. Nothing from my earlier comments is left open, so approving at 12ba68f7.
Implements the entrypoint axis of vllm-project#53194. Asserts that cache_salt partitions the prefix cache end to end, from the HTTP request body through to the block hasher, rather than at the hashing layer alone. Every case pairs a negative arm with a positive control, since a test that only asserts "different salts do not share" also passes when prefix caching is disabled entirely. Tests only; no production file is touched. Signed-off-by: Tejasvi Addagada <tejasvichand@gmail.com>
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Rebased onto current main ( #56199 was already fixed before I opened it, so I have closed it. That has a direct consequence here, and it is the one @rishabhsinha17 predicted — just for a One property of that arm changed with it. It now asserts a validation error, not cache The #47696 arm was the open question and I did not assume it. Re-run against current main it On current main: Mutation-tested by disabling prefix caching, where the four cache-isolation arms fail as they The one that passes there is the empty-salt arm, for the reason above. @rishabhsinha17 — your approvals were given on the premise that #56199 was open, so this head |
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Purpose
Implements the entrypoint axis of #53194, the half left open when @oneKn8 took
the tier axis in #53769. Tests only; no production file is touched.
cache_saltpartitions the prefix cache only if it survives the whole trip froman HTTP request body down to the block hasher.
tests/v1/core/test_prefix_caching.pyasserts that differing salts produce differing block hashes, but it builds
Requestobjects directly, so it begins after the plumbing that keepsregressing.
Five cases over
/v1/completions,/v1/chat/completionsand/v1/embeddings:cache_saltmust not land in a salted namespaceAssertions read
vllm:prefix_cache_hitsrather thanusage.prompt_tokens_details, which is only populated under--enable-prompt-tokens-detailsand is hard-coded to zero on the pooling path.Nothing inspects the extra-key tuple, so this is unaffected by #44706, #51899,
#52655 and #43789, each of which changes that encoding.
What each cited bug gets
Being precise about this, since the motivation is broader than the coverage:
min_length=1) and #51444 (validate_cache_salt), so it pins the rejection rather than the bugHF3FSKVConnectoris a declared rederiver in #53769's exempt map with an evidence pointer, but nothing in-tree executes that path, since CI cannot import the hf3fs clientThe Responses, Anthropic
/v1/messages, classification and scoring endpointsalso accept
cache_saltand are not covered. Worth follow-up.#47696 reproduces on current main
test_chunked_embeddings_isolate_on_saltisxfail(strict=True), so it flipsto a loud XPASS when #47696 lands. Controlled A/B, two identical pooling
servers differing only in
pooler_config.enable_chunked_processing, two trialseach:
One detail wider than #47696's description: the prompt is 256 tokens against a
1024
max_model_len, so it is never actually split. Enabling the flag issufficient — every pooling request takes the rebuild path and loses the salt
whether or not chunking occurs, rather than only long inputs being affected.
Every negative arm is paired with a positive control
Load-bearing rather than stylistic, and I have the receipt. An earlier revision
of the third case asserted only the miss. Run against a server started with
--no-enable-prefix-caching, the other cases failed as intended and that onestill passed — it would have shipped asserting nothing. It now also asserts
that two unsalted requests share with each other, so the miss it reports is the
salt boundary holding rather than the unsalted path never caching.
Verification
Run against real servers on CPU, at 13cf9e0:
Mutation-tested by disabling prefix caching, where every non-xfail case fails.
Two details came out of running it rather than reading:
--gpu-memory-utilizationto size its KV cache fromhost RAM and defaults to 0.92, so the fixtures pin it low to stay runnable on
a developer machine.
per attention backend (
vllm/v1/worker/utils.py), and a fixed--block-size 16passed on CPU while failing to start elsewhere. Nothing here needs to know it.
The pooling arms serve a causal model under
--runner poolingwithLASTpooling, because prefix caching applies to pooling only for last-token or all
pooling with causal attention. A conventional bidirectional embedding model
would never engage the cache, and those arms would pass without testing
anything.
This file is standalone rather than importing
dimensions.pyfrom #53769, sothe two can merge in either order. Unifying them once both land would be an
improvement.
cc @oneKn8 @rishabhsinha17