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feat(sidecar): speak TensorRT-LLM's OpenEngine gRPC API - #14349
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WalkthroughThe sidecar migrates from the native TensorRT-LLM gRPC protocol to OpenEngine v1. It adds vendored protobuf contracts, OpenEngine request and response handling, disaggregated KV handoffs, server-derived context length, deployment updates, and expanded tests. ChangesOpenEngine migration
Estimated code review effort: 5 (Critical) | ~120 minutes Merge Risk: 🔵 Low · up to Malformed protobuf values can be silently changed during JSON handoff conversion. This is a bounded interoperability risk that should be fixed, but it does not otherwise block the OpenEngine migration. 🚥 Pre-merge checks | ✅ 3 | ❌ 2❌ Failed checks (2 warnings)
✅ Passed checks (3 passed)
Full details: Docstring CoverageExplanation Docstring coverage is 43.75% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 96 functions across 15 files. (14 skipped: 14 unsupported.) Full details: Description checkExplanation The description provides a detailed overview, implementation details, validation results, and follow-up context. However, it omits the required Related Issues section and does not identify specific files for the reviewer to inspect first. ✨ Finishing Touches 💡 1⚔️ Resolve merge conflicts 💡
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In `@lib/sidecar/common/src/json.rs`:
- Line 104: Update the protobuf-to-JSON conversion handling for
prost_types::value::Kind::NullValue and an unset kind to return protocol_error
instead of JSON null, preserving rejection of unknown NullValue discriminants.
Add focused tests covering both malformed variants and their protocol errors.
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.pre-commit-config.yamllib/sidecar/common/Cargo.tomllib/sidecar/common/src/json.rslib/sidecar/common/src/lib.rslib/sidecar/trtllm/Cargo.tomllib/sidecar/trtllm/README.mdlib/sidecar/trtllm/build.rslib/sidecar/trtllm/deploy/agg.yamllib/sidecar/trtllm/launch/agg.shlib/sidecar/trtllm/proto/README.mdlib/sidecar/trtllm/proto/openengine/v1/error.protolib/sidecar/trtllm/proto/openengine/v1/generation.protolib/sidecar/trtllm/proto/openengine/v1/kv.protolib/sidecar/trtllm/proto/openengine/v1/lifecycle.protolib/sidecar/trtllm/proto/openengine/v1/lora.protolib/sidecar/trtllm/proto/openengine/v1/model.protolib/sidecar/trtllm/proto/openengine/v1/openengine.protolib/sidecar/trtllm/proto/openengine/v1/server.protolib/sidecar/trtllm/proto/trtllm_service.protolib/sidecar/trtllm/src/args.rslib/sidecar/trtllm/src/client.rslib/sidecar/trtllm/src/convert.rslib/sidecar/trtllm/src/disagg.rslib/sidecar/trtllm/src/engine.rslib/sidecar/trtllm/src/lib.rslib/sidecar/trtllm/src/model.rslib/sidecar/trtllm/src/proto.rslib/sidecar/trtllm/src/tests.rslib/sidecar/vllm/src/convert.rslib/sidecar/vllm/src/lib.rslib/sidecar/vllm/src/tests.rs
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- lib/sidecar/vllm/src/lib.rs
- lib/sidecar/trtllm/proto/trtllm_service.proto
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Reviewed at a9c25a0, base 95cadce (merge base from the compare API — merge_base_commit.sha is null on this PR). Read #14350 first to establish the stack: it targets feat/trtllm-openengine-sidecar, so it is stacked on this branch and its scope is out of scope here.
Intent, as I read it from the diff and description: move lib/sidecar/trtllm off the bespoke trtllm.TrtllmService proto onto TensorRT-LLM's OpenEngine (openengine.v1) surface, and add disaggregated prefill/decode, which the old response contract had no handoff to carry.
One P1 below. Everything else I chased, I could not turn into a finding — the detail is here so the negatives read as decisions rather than gaps.
Proto provenance — verified byte for byte
All eight files under proto/openengine/v1/ are byte-identical to ai-dynamo/openengine at b5f2bd93721f7b888d3e2440679e0ae7012939d1, fetched from the contents API and diff'd; all eight SHA-256s in proto/README.md match those bytes exactly. That commit is what tag v0.1.0 resolves to. The README's harder claim also holds: TensorRT-LLM's requirements-openengine.txt pins BSR module commit 768a93c7b44e40f28c692ad0b471a8f2 and names the same v0.1.0 release as its source. The two launch/agg.sh pins (33.5.0.1.20260730172104+768a93c7b44e, 1.78.1.1.20260730172104+768a93c7b44e) both resolve on the buf.build/gen/python simple index and both carry that module commit — schema-identical to proto/, differing only in generator revision from what TensorRT-LLM's own requirements pin. No drift anywhere.
Hostile input — no panic, no hang, no unbounded allocation
Drove the real TrtllmSidecarEngine against a fake OpenEngine server over a real socket (tonic server, loopback), one case per row:
| peer behaviour | what the caller gets |
|---|---|
| opens the stream, closes OK with no messages | Backend(Unknown) — "Generate ended before a terminal response" |
| one token, then closes without a terminal | same, clean |
a GenerateResponse of 70 MiB |
OutOfRange — "decoded message length too large: found 73400335 bytes, the limit is: 67108864 bytes". The 64 MiB cap is enforced on the declared length before buffering; no attacker-sized pre-allocation |
attributes_struct nested 300 deep (and 40 deep) |
prost's recursion limit rejects the message — no stack overflow. struct_to_json's own recursion is never reached, because prost's limit fires at roughly 33 levels of Struct nesting |
an 8 MiB EngineError.message |
arrives truncated at 4112 bytes — Diagnostic::MAX_BYTES = 4096 (lib/runtime/src/error.rs:581) bounds every DynamoError message, so the peer echo is bounded, not unbounded |
| connects and never sends; aggregated; client cancels | cancelled terminal in 5.25 µs |
A 4 MiB GenerationFinished.stop_match.stop_text does pass through to stop_reason in full — but that is byte-for-byte the base's behaviour (MatchedStopStr(value) => StopReason::String(value) at the merge base), so it is not this PR's and I am not reporting it.
gRPC status → what the caller actually receives
Unimplemented / Internal / Unknown → Backend(Unknown) → HTTP 500, body replaced by the generic internal-error message. InvalidArgument / NotFound / OutOfRange / FailedPrecondition / AlreadyExists → Backend(InvalidArgument) → HTTP 400 with the engine's message forwarded verbatim (bounded at 4 KiB). ResourceExhausted, on Generate only, → WorkerOverloaded → 529 with a sanitized body and router shed/migrate. The in-band EngineError event follows the same table keyed on ErrorCode.
One consequence I checked and am deliberately not reporting: an oversized response from the engine is a server-side framing failure, and it reaches the client as a 400 "InvalidRequest". That comes from OutOfRange => BackendError::InvalidArgument in lib/sidecar/common/src/error.rs, which is pre-existing shared code this PR does not change.
Default path unchanged — proven, with controls
Two controls in the same probe run: no routing at all, and routing present with dp_rank: None. Both produce the metadata-free request and a normal terminal. The vLLM sidecar's codec move is also behaviour-preserving: WHAT = "kv_transfer_params" and peer = "vLLM" reproduce the base's error strings exactly, and cargo test -p dynamo-vllm-sidecar is green (44 passed). The workspace tonic/prost pins (0.13.1 / 0.13.5) are identical to the per-crate pins they replace, so -p dynamo-trtllm-sidecar does not shift protobuf versions; the Cargo.lock diff is additive only.
cargo +1.96.1 test -p dynamo-trtllm-sidecar -p dynamo-sidecar-common -p dynamo-vllm-sidecar — green. trtllm: 42 passed, 2 ignored (the real-engine E2E hooks).
Deliberately not reported
A decode leg that took a handoff and never receives a token ignores client cancellation indefinitely. Measured: with the engine silent, stop_generating() produces nothing for 8 s (the aggregated control cancels in 5.25 µs); only cleanup() breaks the loop. lib/backend-common/src/adapter.rs defers engine.abort() on the same first-token condition, so nothing aborts the engine either. I am not filing it, because lib/sidecar/vllm/src/engine.rs:227-275 has the identical shape today and this PR's version is strictly narrower — it defers only when a handoff was actually taken, where vLLM defers for every decode request. That is a pre-existing cross-sidecar design question and belongs in its own issue, not on this diff.
PR description accuracy (P3, no code anchor). "Notable details" says Control.GetModelInfo "is called once at startup" and "the sidecar refuses to start without a positive value". Neither matches a9c25a0: with no --context-length, wait_for_model_limits polls until --grpc-startup-deadline, and on failure engine.rs logs a WARN and starts anyway with ModelLimits::default(). start_without_a_context_length_registers_a_window_less_worker pins exactly that, and its docstring says "this warns rather than refusing to start". The Validation section's "26 sidecar tests" is likewise from before the split into src/tests/. Worth refreshing before merge — "refuses to start" and "registers a window-less worker that rejects only max_tokens-less requests" are operationally different contracts.
Not verified
The upstream-server behaviour below is read from NVIDIA/TensorRT-LLM main source, not executed against a live TensorRT-LLM process — I have no GPU build of an OpenEngine-capable engine. I reproduced the server's documented rejection rule in a fake server instead, and the sidecar-side result is measured.
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Follow-up to my review above — two findings from finishing the conformance pass against the TensorRT-LLM server's source. Both are the same root cause at two sites: a worker_overloaded mapping whose justifying comment asserts a property of the OpenEngine server that upstream contradicts, and ErrorType::WorkerOverloaded is in Dynamo's migratable set (lib/llm/src/migration.rs, "One overloaded worker: another may have room"), so each one turns into a retry against a different replica.
What makes these worth raising rather than shrugging at is that this PR already made exactly this argument, in the opposite direction. The commit that removed ResourceExhausted from the shared helper wrote into lib/sidecar/common/src/error.rs:
Not WorkerOverloaded: that type is migratable, and a shared helper cannot tell an overloaded engine from a per-request rejection such as an oversized message, which every worker would reject identically. A backend that knows its server means backpressure maps this itself.
That reasoning is right. The two sites below are where it was re-applied on the premise that this particular server does mean backpressure — and against main's source, it does not.
Same verification boundary as before: upstream behaviour is read from NVIDIA/TensorRT-LLM main source, not executed against a live engine. Nothing here changes my read of the rest of the PR.
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Verified all three of my review concerns on 69e7c8b: handoff cancellation is deferred during RPC dispatch, handoff-less prefill terminals preserve requested logprobs and candidates, and the context-length documentation matches the implementation and the inspected upstream server source at 8bbaf66bd5.
Validation: 101 tests passed across the TRT-LLM, vLLM, and common sidecar crates, plus all three independent regression repros that failed on the original revision. These ran on 566c68e; I inspected the subsequent 69e7c8b commit and verified that only comments changed, with executable code and tests unchanged. The two real-engine E2E tests remain ignored.
CI is still pending separately. The latest docs composition job failed fetching docs-website (non-fast-forward), before docs validation; the earlier Python-bindings Rust job failed downloading protoc (HTTP 500), before compilation or tests.
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Re-reviewed at 69e7c8bb4, base 95cadce. The head moved twice while I was working. I started at 566c68e85 and retargeted. Everything below is measured at 69e7c8bb4.
69e7c8bb4 changes two doc comments and nothing else. It renames the build the evidence was measured against, from the version string 1.3.0rc26 to the commit 8bbaf66bd5, in client.rs:88-93 and convert.rs:392-398. git diff 566c68e85..69e7c8bb4 is 2 files, +8/-8, and every changed line is a comment. That matches what my first-round review found from the API: the published v1.3.0rc26 tree carries no OpenEngine servicer, so the version string named a build that cannot have produced the measurement.
Test churn across three commits: nothing was lost
I enumerated every annotated test under lib/sidecar/trtllm/src/ at a9c25a0, 566c68e85 and 69e7c8bb4, so a test deleted in one commit and not restored in the next cannot hide in the gap.
| point | annotated tests | removed | added |
|---|---|---|---|
a9c25a0 |
44 | ||
566c68e85 |
44 | each_leg_forwards_its_own_data_parallel_rank, a_decode_request_cancelled_before_dispatch_stops_immediately |
a_data_parallel_rank_hint_is_rejected_before_dispatch, a_cancelled_decode_dispatch_is_not_abandoned_mid_flight |
69e7c8bb4 |
44 | none | none |
The name set at 69e7c8bb4 is byte-identical to the one at 566c68e85.
Both removals assert behavior this round deleted, so an equivalent assertion cannot survive and must not. each_leg_forwards_its_own_data_parallel_rank asserted that each leg sends its own rank as openengine-target-dp-rank. That is the P1 I raised. Its replacement asserts the opposite and adds assert!(server.service.requests.lock().await.is_empty()), which the old test had no reason to make. a_decode_request_cancelled_before_dispatch_stops_immediately asserted that a cancelled decode dispatch returns at once, which is the behavior nv-yna flagged as wrong. Its replacement asserts the dispatch outlives the cancellation and that shutdown still releases it.
The 8 deleted lines in src/tests.rs are the fake server's dp_ranks capture. They have no reader left once the metadata is gone.
The rewrite does not weaken assertions. convert_response.rs flips assert!(matches!(overloaded.error_type(), ErrorType::WorkerOverloaded)) to assert!(!matches!(...)), which is the point of the change. disagg.rs adds three assertions and removes none.
Test counts
Local, cargo test -p dynamo-trtllm-sidecar --lib on macOS ARM64, at each of the three commits:
running 44 tests
test result: ok. 42 passed; 0 failed; 2 ignored; 0 measured; 0 filtered out
In CI, rust-tests (.) at a9c25a0 reports the same 42 passed and 2 ignored for dynamo_trtllm_sidecar, and the two tests this round removed both appear as ... ok there, so they ran rather than skipped. The push to 69e7c8bb4 cancelled the job at 566c68e85, so no count exists there, and rust-tests (.) at 69e7c8bb4 was still in progress when I posted. The three local runs cover the gap.
Mutation results
Each behavior this round names, reverted one at a time at 69e7c8bb4:
| reverted | test | result |
|---|---|---|
the dp_rank guard in validate_request |
a_data_parallel_rank_hint_is_rejected_before_dispatch |
FAILED |
Overloaded => engine_error back to worker_overloaded |
engine_error_codes_the_router_acts_on_are_preserved |
FAILED |
the dispatch-site if !defer_request_cancellation guard |
a_cancelled_decode_dispatch_is_not_abandoned_mid_flight |
FAILED |
held.extend(token.tokens) back to token IDs only |
a_prefill_terminal_without_a_handoff_carries_its_tokens |
FAILED |
All four pass unmutated. One gap remains, and it is the P3 below.
The three findings nv-yna raised
These are not my threads and I did not touch them. nv-yna resolved all three. I checked each by execution because this round claims to fix them.
engine.rs:282, deferred cancellation during submission: fixed, on both timings. The author took the suggested diff. I drove an already-stopped context into generate, which is the timing the author's own test does not cover, and added three controls:
[decode + handoff] dispatched_to_engine=true terminal=None
[decode, no handoff] dispatched_to_engine=false terminal=Some(Cancelled)
[agg CONTROL] dispatched_to_engine=false terminal=Some(Cancelled)
[prefill CONTROL] dispatched_to_engine=false terminal=Some(Cancelled)
A decode leg that took a handoff now reaches the engine even when the context is already stopped, and the three non-deferring shapes still short-circuit.
convert.rs:552, held tokens lose their logprobs: fixed. Answered by execution below.
client.rs:93, the doc comment disagreed with filter(|len| *len > 0): fixed. The comment now reads "Reads the server's advertised limits, keeping positive values." The same wrong claim is gone from the three other places it appeared: args.rs:22-27, README.md:104-109 and launch/agg.sh:68-70. grep -rE '1\.3\.0rc2[0-9]' lib/sidecar/trtllm/ returns nothing at this head.
Does the client get the logprobs it asked for?
Yes. I drove ResponseState directly rather than reading the branch: prefill mode, two held tokens, each carrying a logprob and two candidates, then Finished(Stop) with no PrefillReady.
[logprobs=2] ids=[7, 8] log_probs=Some([-0.1, -0.2]) top_len=Some([2, 2])
[logprobs=2] cand ids=[[70, 71], [80, 81]]
[logprobs=0] ids=[7, 8] log_probs=Some([-0.1, -0.2]) top=false
[logprobs=None CONTROL] ids=[7, 8] log_probs=None top=false
[logprobs=2, engine omits logprob] err=Internal: invalid TensorRT-LLM gRPC response: token 7 is missing its logprob
Both controls hold. With logprobs unset the terminal carries the IDs and no logprobs. With logprobs=0 it carries the selected-token logprobs and no candidates, which matches the vLLM contract the code cites. The same probe on a9c25a0 prints log_probs=None top_len=None and then fails, so the fix is measured in both directions.
The last row is a behavior change worth naming. A held token that arrives without its logprob, while logprobs were requested, is now a protocol error instead of a silent drop. That is map_tokens doing its job, and it is the right call, but it turns an engine bug into a failed request on a path that used to answer.
My four findings from the first round
| finding | status | what I ran |
|---|---|---|
P1, openengine-target-dp-rank makes the engine reject the RPC |
fixed | all four rank shapes now return Backend(InvalidArgument), and 0 of them reach the fake engine |
P2, RESOURCE_EXHAUSTED mapped to a migratable overload |
fixed | generate_status is gone. status_to_dynamo("Generate", ResourceExhausted) gives Backend(Unknown) |
P2, ERROR_CODE_OVERLOADED mapped to a migratable overload |
fixed | engine_error(Overloaded) gives Backend(Unknown), not WorkerOverloaded |
| P3, unescaped peer text in a default-level log line | fixed | the rendered line carries \n as two characters, has_newline=false |
Measured at 69e7c8bb4:
[dp-rank Aggregated] type=Backend(InvalidArgument) msg=InvalidRequest: data-parallel rank targeting is not supported by the TensorRT-LLM sidecar
[dp-rank Aggregated] type=Backend(InvalidArgument) msg=... (rank 0)
[dp-rank Decode] type=Backend(InvalidArgument) msg=...
[dp-rank Prefill] type=Backend(InvalidArgument) msg=...
[CONTROL no routing] outputs=2 terminal=Some(Some(Stop))
[CONTROL routing, ranks None] outputs=2 terminal=Some(Some(Stop))
[dispatched to engine during dp-rank cases + controls] = 2
[ResourceExhausted] type=Backend(Unknown) msg=Internal: Generate: too big (ResourceExhausted)
[ErrorCode::Overloaded] type=Backend(Unknown) msg=Internal: TensorRT-LLM engine error: response consumer stalled
[abort log render] has_newline=false body=Internal: Abort: engine says:\n[FORGED level=ERROR] injected\ntail (Internal)
The two controls are the only two requests that reached the engine, so the guard rejects before dispatch and leaves the default path alone. I resolved all four of my threads with the output above.
Checked and not reported
Phase::Prefill now holds Vec<pb::TokenInfo> instead of Vec<u32>, so a token costs a struct with its candidate list instead of 4 bytes. The prefill request caps stopping.max_tokens at 1, so the hold is bounded for an engine that honors the cap, and the count was already unbounded for one that does not. This PR raises the per-token constant and does not create the shape, so I am not filing it.
The commit title names two behaviors, and I checked whether one of them landed less completely than the other. Both are complete. No openengine-target-dp-rank plumbing survives anywhere outside comments and the vendored protos, and ERROR_CODE_OVERLOADED has exactly one mapping site.
Approving. The one open item is the P3 below, which is a test gap and not a defect.
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Re-approving 5f3cef972.
The approval that went stale was not dismissed by a rewrite. 69e7c8bb4 is still an ancestor of the head, the merge base with main is the same commit before and after, and the single new commit touches only the README, the launch script, and the deploy manifest. No Rust, proto, or Cargo.toml byte moved, so the four findings I filed stay fixed.
I re-ran the tests and the three claims that commit adds, against the image it now names.
Push shape: a fast-forward of one docs commit, not a force-push
| check | result |
|---|---|
compare 69e7c8bb4...5f3cef972 |
status: ahead, ahead_by: 1, behind_by: 0 |
merge base with main, at 69e7c8bb4 |
95cadce97d |
merge base with main, at 5f3cef972 |
95cadce97d (same) |
commits from main since the approval |
0 |
git diff 69e7c8bb4 5f3cef972 -- 'lib/**/*.rs' 'lib/**/*.proto' 'lib/**/Cargo.toml' |
empty |
Green at the live head, and the connection failure is bounded
$ cargo test --no-default-features -p dynamo-trtllm-sidecar -p dynamo-sidecar-common
test result: ok. 42 passed; 0 failed; 2 ignored (trtllm sidecar lib)
test result: ok. 11 passed; 0 failed; 0 ignored (sidecar common lib)
test result: ok. 1 passed; 0 failed; 0 ignored (doc tests)
Dead port, no server, through GrpcChannelPool::connect:
Unavailable: failed to establish the test gRPC connection pool to
http://127.0.0.1:56213 for pool slot 1 within 100ms after 8 attempts over
101.540834ms: transport error: tcp connect error: Connection refused (os error 61)
Retries are capped by --grpc-startup-deadline, and what is echoed is the operator's own endpoint, not anything a request carries.
The new commit's three claims reproduce on the named image
Pulled nvcr.io/nvidia/tensorrt-llm/release:1.3.0rc27.dev202609170000 (manifest HTTP 200) on an RTX 6000 Ada box.
| claim | measured |
|---|---|
| the release carries the servicer | tensorrt_llm/grpc/openengine/ holds 2092 lines across 10 modules, with a real OpenEngineControlServicer and OpenEngineInferenceServicer |
| the bindings are not installed | import openengine → ModuleNotFoundError: No module named 'openengine' |
| the pins resolve against the image's protobuf | both pinned wheels install, from openengine.v1 import openengine_pb2_grpc imports, and google.protobuf.__version__ is still 6.33.6 |
The vendored protos still match their recorded pin: all 8 files hash to the SHA-256 values in proto/README.md, at commit b5f2bd93, the git revision behind BSR module commit 768a93c7b44e — the same revision the bindings I installed are built from.
Not a finding, just a note for the wording: release:1.3.0rc26 does ship a tensorrt_llm/grpc/openengine/server.py, but it is a 100-line stub that binds the base InferenceServicer/ControlServicer and ignores the engine entirely, so every RPC answers UNIMPLEMENTED. Your floor is right in effect, and answers_the_request_is_wrong in client.rs makes that skew fail fast at startup instead of burning the deadline.
Still open, unchanged and non-blocking: the P3 note on engine.rs:278, that no test pins the guard's non-deferring branch.
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Reviewed bfd71c90c54517842dbbac08d07957cfb982ef18. Approving with the inline P2 about preserving prefill min_tokens left open.
Validation: the unmodified-head test run across the TensorRT-LLM, vLLM, and common sidecar crates passed 101 tests; the two real-engine E2E tests were ignored. The inline finding is backed by a separate converter regression probe and CPU execution of the pinned upstream EOS-mask logic; no real GPU E2E run was performed for this review.
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Re-approving at f96a6410ca.
The head moved twice while I was reviewing, from 5f3cef972 to bfd71c90c5 and then to f96a6410ca. Both pushes are fast-forwards that append commits, not rewrites. I confirmed that three ways each: the earlier commit is still an ancestor of the new head, the compare endpoint reports ahead by 2 and behind by 0 for both steps, and the fetch lines printed 5f3cef9727..bfd71c90c5 and bfd71c90c5..f96a6410ca with no forced update. The merge base did not move, so the incremental diffs are the whole change.
What the four new commits change, and what I verified
The flag rename is correct, and the old text was wrong. The real flag is defined at lib/sidecar/common/src/args.rs:54 as long = "grpc-startup-deadline-secs". The old remediation string told an operator to raise --grpc-startup-deadline, which clap rejects. After the change, zero occurrences of the bare name remain in any .rs, .md, .yaml or .sh file. The name stays pinned by the parser tests at args.rs:144 and args.rs:161.
The manifest pins are self-consistent. Both deploy/agg.yaml and deploy/disagg.yaml pass --max_seq_len 4096 to each engine and --context-length 4096 to each sidecar. --context-length is a real sidecar flag (lib/sidecar/trtllm/src/args.rs:28, long, u32 in range 1..), and the launch scripts pin the same pair at the same default. The two values agree, so the WARN path for a disagreement does not fire. The mounted engine configuration sets only cache_transceiver_config and stream_interval, so nothing overrides max_seq_len later in the argument list.
The min_tokens fix is proven, not just plausible. See my reply on that thread.
The new disaggregated launcher holds together on the points a reader cannot guess. Every helper it sources exists: build_trtllm_override_args_with_mem and its --merge-with-json flag in examples/common/gpu_utils.sh, and print_launch_banner, wait_any_exit and dynamo_reap_and_exit in examples/common/launch_utils.sh. That helper reads no GPU state, so sharing one generated configuration file across two engines on two devices introduces no per-device skew. Both engine configurations in deploy/disagg.yaml carry cache_transceiver_config, which is the part that silently breaks the handoff when it is missing on one leg. Prefill and decode get one GPU each, separate gRPC ports, and separate system ports.
The image floor did not move. An anonymous manifest request for nvcr.io/nvidia/tensorrt-llm/release:1.3.0rc27.dev202609170000 returned HTTP 200 with a 1611-byte manifest. Round 2 established that this release carries the servicer and not the bindings, and the docs, the launcher and the manifests all say so.
The eight vendored protocol files are untouched by all four commits, so the pin still holds by identity against the round 2 table. The four findings closed in rounds 1 and 2 also hold: engine.rs is byte-identical to the approved tree, and the only other Rust change outside the min_tokens fix is three text lines.
Suite at the live head: 42 passed, 0 failed, 2 ignored, plus the executable test. cargo test --no-default-features -p dynamo-trtllm-sidecar, macOS ARM64.
One item stays open, and I am approving with it.
lib/sidecar/trtllm/src/engine.rs:278 (P3, mine). The false branch of the deferral guard is still unpinned. At the live head, replacing the condition with an always-defer form leaves all 42 tests green, while removing the guard fails a_cancelled_decode_dispatch_is_not_abandoned_mid_flight. The behavior is correct today. Only the test is missing.
I did not apply either manifest to a cluster, and the author states that limitation in the commit and on the docs page.
Combined P2 and P3 count is one, and there is no P0 or P1 outstanding.
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Second source review at eba63f1 using graham-code-review. The original minimum-token case is fixed when both workers use the same limits, and the four smaller comments are addressed. Two findings remain below. I did not run tests or inspect CI for this pass.
…'s window The prefill-side minimum check used this worker's own context length, but the minimum applies to the decode worker's budget and discovery pairs the two roles without requiring equal windows. A 4096-token prefill window against an 8192-token decode window rejected requests the decode worker had room for, and the reversed pairing still let a handoff through for decode to refuse. The local limit establishes neither result, so drop the check and pin that decision in a test. Releasing the handoff when decode rejects is the sound fix and belongs on the decode side. Also refresh the README's startup description: with neither `--max_seq_len` nor `--context-length` the sidecar now fails on the engine's first answer instead of retrying to the startup deadline. Signed-off-by: tanmayv25 <tanmay2592@gmail.com>
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Approved with the condition:
What about removing this part:
IPC_LOCK", "SYS_RESOURCE"
I do not think this is harmless
The sidecar version mismtach is ok to fix in a followup
I withdraw this approval. At e229af3, the stranded handoff from round 11 is open again, and it is a P1. My review at that head gives the numbers.
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I withdraw my approval. At e229af3270, the round-11 P1 is open again: a request that the decode worker refuses holds the KV blocks of the prefill worker for 60 s, and valid requests wait behind it.
- [P1, open]
convert.rs:52: with the equal windows thatdisagg.shsets, a valid request waited 53.98 s behind two refused requests. Ateba63f1b9b, it took 0.07 s. See my reply. - [P2, fixed]
convert.rs:225from @jthomson04: his pairing, a 4096-token prefill window with an 8192-token decode window, now gets 200. - [P3, fixed]
README.md:106from @jthomson04: the new text matches what the sidecar does.
What I ran at e229af3270, and where I stopped.
- Tests:
cargo test -p dynamo-trtllm-sidecar --libgives 51 passed and 2 ignored. With theconvert.rsofeba63f1b9b, onlya_prefill_request_does_not_judge_a_minimum_against_its_own_windowfails. - GPU:
disagg.shwith three window pairings at each head. My reply has the table. - README: against an engine started without
--max_seq_len, the sidecar with neither setting exits after 0 s, and its error names both fixes. With--context-length 4096, as the README shows, it starts. - My approval at
eba63f1b9bcounted the stranded handoff as fixed. With the windows reversed, it was not. @jthomson04 found that. - I dismissed my four approvals, at
8867681f7c,18c894a70f,11ac6520d7, andeba63f1b9b.
Signed-off-by: tanmayv25 <tanmay2592@gmail.com>
Signed-off-by: tanmayv25 <tanmay2592@gmail.com>
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@dmitry-tokarev-nv See my response here: #14349 (comment) |
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No approval yet: the P1 stays open until a tracking issue and a known-issue note exist. I read 4cba3229e0.
- [P1, open] Re your reply: your reason to defer holds. I accept the deferral once two things exist: a tracking issue for the session-level abort, and a known-issue note that users can see, in the README Disaggregation section or a docs page. When both exist and the rest of the bar holds, I will approve.
- [P3, new, not blocking] On a natural stop, the client gets no
usage.prompt_tokens_details.cached_tokens, because the usage from the engine never reaches it.lib/sidecar/trtllm/src/convert.rs:699.
P1: what I checked at 4cba3229e0.
- The P1 path did not change. Of the 41 files under
lib/sidecar/trtllmandlib/sidecar/common, 40 have the same blob as ate229af3270, where a valid request waited 53.98 s. The one that changed isdeploy/disagg.yaml. - The reason also holds on the version that
mainnow uses. #15215 movedmainto TensorRT-LLM 1.3.0rc28, and itstensorrt_llm/grpc/openengine/control.pyis byte-identical to the rc27 file (SHA-256 prefixbce968ed33187345).Abort(kv_session)still returnsUNIMPLEMENTEDthere. - For the note: the hold lasts
cache_transceiver_config.kv_transfer_timeout_ms, 60000 ms by default, and neitherlaunch/disagg.shnordeploy/disagg.yamlsets it. The hold starts after the decode worker refuses a request that prefill already ran, for example amin_tokensthat the decode window cannot fit. Valid requests that need those blocks wait until it ends.
P3: Qwen3-0.6B on one GPU, aggregated, chat with and without streaming.
TensorRT-LLM streams the end-of-sequence token and then sends finished, with the usage, as a separate message. The frontend ends the stream at that token (lib/llm/src/backend.rs:238), so it never reads the terminal chunk from the sidecar. The sidecar at main reported no cached tokens at all, so this is a gap in the new feature, not a regression.
| How the request ends | This PR | main, in-process dynamo.trtllm |
|---|---|---|
| Natural stop | no cached_tokens |
cached_tokens: 18 |
Length stop, max_tokens=1 |
cached_tokens: 18 |
cached_tokens: 18 |
- The gRPC stream of the natural stop: tokens
[9693, 151645], thenfinishedwithstop_match.eos_token_id=151645. - Control: I added
9693to the end-of-sequence ids in a copy ofgeneration_config.json. TensorRT-LLM then removes that token from the stream, the frontend reads the terminal chunk, andcached_tokens: 18arrives. - The frontend metrics read the same field (
lib/llm/src/preprocessor.rs:5421). cached_prompt_tokens_reach_the_client_on_both_pathschecks the output of the sidecar, not the response, so it passes.- The disaggregated decode leg uses the same frontend path. I did not run it.
- A possible fix: if a token event ends on a hidden stop id of the request, wait for the next message. Then merge its usage into that chunk. Other tokens do not wait.
Signed-off-by: tanmayv25 <tanmay2592@gmail.com>
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No approval yet, because the known-issue note for the P1 is missing. I read 69147a2bb3. If nothing else changes, I will approve as soon as the note lands.
- [P1, deferred to #15404] A request that decode refuses after prefill ran still holds the prefill KV blocks until
kv_transfer_timeout_msends. At this head, on TensorRT-LLM 1.3.0rc28, a later valid request waited 53.98 s. - #15404 meets the tracking part of my condition. It states the cause, the planned fix (a session-level abort through
Abort(kv_session)), and a test: my refused-request sequence at three window pairings. - Please add the known-issue note, in the Disaggregation section of
lib/sidecar/trtllm/README.mdor on the sidecar docs page,docs/fern/pages/developer-guide/knowledge-base/modular-components/backends/tensorrt-llm/sidecar.md. The note needs to say these three things:- A request that decode refuses after prefill ran holds the prefill KV blocks until
kv_transfer_timeout_msends, 60000 ms by default. - Later requests can wait during that time.
- #15404 tracks the fix.
- A request that decode refuses after prefill ran holds the prefill KV blocks until
- [P3, open, not blocking] On a natural stop, the client still gets no
usage.prompt_tokens_details.cached_tokens.lib/sidecar/trtllm/src/convert.rs:699.
P1: four runs at 69147a2 on one GPU, one of them a control.
Setup: Qwen3-0.6B, with both engines on one RTX 6000 Ada. Each engine has 256 KV blocks (8192 tokens) and a 4096-token window. The sidecar is built at this head. The refused requests have a 3000-token prompt, min_tokens=4096, and no max_tokens. The valid requests have a 3000-token prompt and max_tokens=8.
| TensorRT-LLM | The two refused requests | Next valid request | Prefill engine timeout for the first refused request |
|---|---|---|---|
| 1.3.0rc28 | 400, decode refuses after prefill | 200 in 53.98 s | elapsed 60000ms > kv_transfer_timeout_ms=60000ms |
1.3.0rc28, kv_transfer_timeout_ms: 20000 |
400, decode refuses after prefill | 200 in 9.96 s | elapsed 20001ms > kv_transfer_timeout_ms=20000ms |
| 1.3.0rc28, control | 400 from the frontend (n=2 at temperature 0) |
200 in 0.07 s | none, because no worker got it |
| 1.3.0rc27 | 400, decode refuses after prefill | 200 in 53.98 s | elapsed 60000ms > kv_transfer_timeout_ms=60000ms |
- The prefill blocks of the first refused request stayed held for 60 s, or 20 s with
kv_transfer_timeout_ms: 20000. The valid request was sent 6 s after the first refused request, 10 s in the 20000 ms run, and at once in the control. In the runs with a wait, the valid request finished in the same second as the timeout line of the prefill engine. That was 60.1 s after the first refused request, or 20.1 s with 20000 ms. - The request counters of the two sidecars show that prefill ran each refused request and decode refused it. In the control, neither counter moved.
- For the three runs on 1.3.0rc28, the engines ran in
nvcr.io/nvidia/tensorrt-llm/release:1.3.0rc28, which is the base image of the build at this head. The frontend and the two sidecars ran in a second container in the same network namespace. That container used the image of my earlier measurement, with the sidecar built at this head. The 1.3.0rc27 run usedlaunch/disagg.shunchanged in that image.
P3: the same result at this head, on TensorRT-LLM 1.3.0rc28.
| How the request ends | cached_tokens in the response |
|---|---|
| Natural stop, with or without streaming | none |
Length stop, max_tokens=1 |
18 |
convert.rs and lib/llm/src/backend.rs have the same content as at 4cba3229e0, where I first measured this.
Signed-off-by: tanmayv25 <tanmay2592@gmail.com>
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Approve. I read c832e5d148, and the new known-issue note matches what I measured.
- [P1, tracked in #15404] A request that decode refuses after prefill ran holds the prefill KV blocks until the engine transfer timeout ends. The new "Known issues" section of
lib/sidecar/trtllm/README.mdsays so and links #15404. - [P3, open, not blocking] On a natural stop, the client still gets no
usage.prompt_tokens_details.cached_tokens.lib/sidecar/trtllm/src/convert.rs:699.
What I measured at c832e5d, with controls.
The change since 69147a2bb3 is 7 added lines in lib/sidecar/trtllm/README.md. The other 5971 tree entries are identical. The links #known-issues and #run resolve, and the pre-commit hooks pass on the README.
I tested each claim of the note on nvcr.io/nvidia/tensorrt-llm/release:1.3.0rc27.dev202609170000, the tag that Run names. launch/disagg.sh at this head started both engines on one GPU, with 256 KV blocks each. I sent the requests to the engines over gRPC.
| Claim | Result |
|---|---|
Decode refuses before its Generate RPC |
After the prefill leg ran, a decode request with the handoff and min_tokens=4096 got InvalidRequest. It sent 0 Generate calls to the fake OpenEngine server of the crate tests. With min_tokens=8, it sent 1. |
| The hold lasts 60 s | kv_transfer_timeout_ms defaults to 60000 in this tag and in rc27, rc28 and rc29. After two unclaimed handoffs, a valid 3000-token request took 54.12 s. It finished 60.08 s after the first handoff. |
Session abort returns UNIMPLEMENTED |
Abort(kv_session) right after PrefillReady returned the gRPC status UNIMPLEMENTED. |
| Abort by request ID does not release the handoff | Abort(request_id) right after PrefillReady returned ABORT_STATUS_ALREADY_FINISHED. The next valid request still took 54.11 s. The engine then logged elapsed 60000ms > kv_transfer_timeout_ms=60000ms for that handoff. |
Controls: with nothing held, a valid 3000-token request took 0.07 s. After two handoffs that decode claimed, it also took 0.07 s, and the engine logged no timeout for them. Abort(request_id) of a running request returned ABORT_STATUS_ABORTED and ended its stream after 19 tokens. After each 60 s timeout, a valid request took 0.07 s and 0.06 s.
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Summary
TensorRT-LLM is adding OpenEngine (
openengine.v1) as its gRPC surface. This migrateslib/sidecar/trtllmoff the bespokeTrtllmServiceprotocol and adds disaggregated serving, which the old protocol had no representation for.Vendored protos, not the BSR. The Buf Schema Registry Rust SDK needs a per-developer token to build — a bad first-run experience — and it pinned this crate to a different tonic version than the rest of the workspace. The protos are vendored instead, with
proto/README.mdrecording the upstream commit and a SHA-256 per file so the copies stay verifiable.Disaggregation follows the protocol's own shape. A prefill worker marks its request
context_onlythroughextraand terminates withPrefillReadyinstead offinished; the decode worker replays the returnedKvSessionRefverbatim. The handoff is opaque JSON, sodisagg.rsowns the codec and refuses anything it cannot round-trip — non-finite numbers, integers past 2^53, a missing endpoint port.Shared JSON codec.
json.rsmoves from the vLLM sidecar intodynamo-sidecar-common, since both sidecars now need Struct↔JSON conversion. Behaviour and error text are unchanged.Notable details
FinishReason::Length. The frontend's prefill router treats any other terminal reason as "already complete" and never runs the decode leg.Control.GetModelInfois called once at startup for the model's context length;--context-lengthsupplies it when the engine reports none, which is what an engine started without--max_seq_lendoes.Control.Abort.Validation
cargo test -p dynamo-trtllm-sidecar -p dynamo-vllm-sidecar -p dynamo-sidecar-common— all green (26 sidecar tests, 2 ignored real-engine E2E hooks).cargo clippy --workspace,cargo fmt --all, and the full pre-commit suite pass.xgrammar. Disaggregated runs confirmed genuinely split — the frontend logged distinctprefill_worker_idanddecode_worker_id— over the NIXL cache transceiver.Review round, measured against a local build of TensorRT-LLM main at
8bbaf66bd5, the commit that introduced the OpenEngine servicer. (The build's in-tree version string reads1.3.0rc26, but the publishedv1.3.0rc26tree does not carry the servicer — the commit is the meaningful identifier.)openengine-target-dp-rankis rejected withUNIMPLEMENTEDat every rank, including 0, as isopenengine-priority; a request carrying neither succeeds. The sidecar now refuses a rank hint invalidate_requestrather than letting the engine fail it.--max_seq_lenanswersGetModelInfowithmax_context_lengthunset — it does not substitute a placeholder. Docs corrected accordingly.RESOURCE_EXHAUSTEDis emitted nowhere in the installedtensorrt_llm;ERROR_CODE_OVERLOADEDhas a single emitter, the consumer-stall watchdog. Both mappings changed to match.Re-validated on the published release
nvcr.io/nvidia/tensorrt-llm/release:1.3.0rc27.dev202609170000, the first public tag carrying the OpenEngine servicer (TinyLlama-1.1B, RTX 5880 Ada, through the Dynamo frontend)./v1/completionswithlogprobs=2(token_logprobsandtop_logprobsboth populated), and a request omittingmax_tokensserved from the registered context window.KvCacheTransceiverV2 ... TransferWorker readyon both engines and the prefill and decode sidecars each logging all four — zero warnings on either.openengine-target-dp-rank(ranks 0 and 3) andopenengine-priorityboth returnUNIMPLEMENTED, while the same request without metadata succeeds;GetModelInforeportsmax_context_lengthunset for an engine started without--max_seq_len, whose own args logmax_input_len=1024 max_seq_len=None; and statically,ERROR_CODE_OVERLOADEDhas one emitter (servicer.py:241),RESPONSE_STALL_TIMEOUT_SECONDS = 30.0(streaming.py:27), the rank/priority rejection sits atrequest_mapping.py:189, andRESOURCE_EXHAUSTEDappears in zero files.control.py:258now states it outright:supports_priority = False # Generate rejects openengine-priority.InvalidRequest: data-parallel rank targeting is not supported by the TensorRT-LLM sidecarinstead of a 5xx out of the engine.openengine.v1bindings it imports, so a stock image exits withFailed to import OpenEngine support: No module named 'openengine'. The docs, launch script, and manifest now name the release as the floor and keep the pinned pip step (the pins resolve cleanly against its protobuf 6.33.6).Follow-up
#14350 adds a CPU-only mocker server for this protocol and is stacked on this PR.
Summary by CodeRabbit
New Features
Documentation
Breaking Changes