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test(stargate): add discrete-event routing simulator - #2223
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Included review availability: This review used your included allowance. Your plan provides up to 12 included reviews per hour; 2 remain after this review. 📝 WalkthroughWalkthroughAdds a Rust command-line simulator that runs Stargate load balancers against simulated backends. It supports configurable topology, policies, and fixed or growing workloads, and reports routing, latency, failure, and backend metrics. ChangesRouting simulation
Priority: ⬇️ Low Estimated code review effort: 4 (Complex) | ~60 minutes Change: Feature Sequence Diagram(s)sequenceDiagram
participant main
participant SimConfig
participant sim_run as sim::run
participant LoadBalancer
participant Backend
participant summarize as metrics::summarize
main->>SimConfig: Deserialize and validate configuration
main->>sim_run: Run each seed, rate, and policy
sim_run->>LoadBalancer: Request a backend route
LoadBalancer-->>sim_run: Return a backend choice or wait
sim_run->>Backend: Deliver request and advance engine
Backend-->>sim_run: Return engine events and backend stats
sim_run->>summarize: Summarize request records
summarize-->>main: Return run summary
Merge Risk: 🔵 Low · up to The simulator remains mergeable with owner awareness that sufficiently long virtual runs may panic. 🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
✅ Passed checks (4 passed)
Full details: Docstring CoverageExplanation Docstring coverage is 36.73% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 98 functions across 12 files. (1 skipped: 1 unsupported.) ✨ Finishing Touches📝 Generate docstrings
🧪 Generate unit tests (beta)
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@src/libraries/rust/stargate/crates/stargate-routing-sim/src/config.rs:
- Around line 209-218: Update Config::validate to reject non-finite or negative
values in rtt_ms, intra_region_rtt_ms, stats_relay_delay_ms, and warmup_s, and
reject non-finite or non-positive measure_s. Return validation errors that name
each offending field, while preserving the existing RTT matrix shape check.
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@src/libraries/rust/stargate/crates/stargate-routing-sim/src/sim.rs:
- Around line 403-409: Update the received_at calculation in the simulator’s
elapsed-time handling to avoid panicking when checked_sub cannot represent the
virtual elapsed time; use Instant::now() as the fallback while preserving the
existing backdating behavior when subtraction succeeds.
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Drive the production wait-and-widen, pulsar-wait-and-widen, and power-of-n load balancers in virtual time so policy configurations can be swept in seconds instead of cluster hours. The simulator models stale per-Stargate stats with reservations, the proxy routing wait and retry loop, Pylon queue-mismatch admission and fallback input-throughput estimates, the MockDynamo engine and KV cache, inter-region latency, and client timeouts. Includes a stargate-dev parity config, unit tests, and Bazel targets. Relates to #2222 Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Signed-off-by: Barry Greengus <bgreengus@nvidia.com>
…rowing sessions Update the routing simulator to the current model of the system: - Backends run the mock-engine crate that MockDynamo also uses: batched GPU workers with chunked prefill, per-worker KV caches with cached output, and perfect KV routing between workers. Per-backend GPU counts are configurable. - Pylon can publish stats on request state changes with a coalescing window, in addition to heartbeats. - Workloads are either fixed-prompt sessions or growing conversations whose prompts extend each turn. Failed turns retry with backoff before a session is abandoned. - Results include a per-backend breakdown. The mock-engine crate matches the copy in #2286 and drops out of this diff once that change merges. Relates to #2222 Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Signed-off-by: Barry Greengus <bgreengus@nvidia.com>
Add tests that run small fixed and growing workloads through power-of-n, wait-and-widen, and pulsar-wait-and-widen, and assert that every measured request has exactly one outcome. After each run, a debug assertion checks that every simulated Pylon is idle, which catches phase or prompt-work accounting leaks. Reject consider_kv_free_tokens policies at validation, because simulated Pylons publish no KV-cache stats and every candidate would be skipped. Remove the never-empty Option around per-Stargate stats, compute each backend engine config once, and document the heartbeat-only publish default, retry scope, growing sessions, and the 1-9 ms retry sleep. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Signed-off-by: Barry Greengus <bgreengus@nvidia.com>
The end-to-end tests never timed out a request, so the cancel path and turn retries went unchecked. Add a short-timeout growing-session test that requires timeouts and retries for every policy and an abandoned session for at least one. The end-of-run debug checks now also require every request resolved and every engine empty. Validation rejects configs that would hang or misroute instead of failing: a zero heartbeat, non-positive rates, negative or all-zero traffic weights on Stargate regions, and a zero region gpu_workers. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Signed-off-by: Barry Greengus <bgreengus@nvidia.com>
The routing simulator truncated a load balancer's remaining wait to whole microseconds. Real-clock jitter in received_at.elapsed() left sub-microsecond remainders at the end of an affinity window, which became zero and failed the request as no-route instead of widening. Round the wait up and add a regression test with no max-wait header. Review cleanup in the same crate: - Call the router's own reservation and queue-estimate functions instead of local copies, exported from the stargate crate as routing::apply_reservation and routing::queue_time_estimate_ms_for_priority. - Validate delays, RTT symmetry, measure_s, input TPS rates, the fallback window, session_zipf_s, and timeout_ms instead of silently clamping them. - Pass backends to summarize instead of re-deriving their order, drop the identity candidate index map, and keep reservation IDs out of metrics. - Reject --jobs 0 and add run context to simulation errors. - Document measurement assumptions and match the Bazel test naming. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Signed-off-by: Barry Greengus <bgreengus@nvidia.com>
A pylon.heartbeat_ms that rounds to zero microseconds rescheduled its heartbeat at the same instant forever and hung the routing simulator. Require at least one microsecond. Second review pass cleanup in the simulator: - Count a reroute that excluded every cluster as exhausted retries, as the proxy does, instead of no-route, and test it on a single backend. - Make a double resolve panic in release builds instead of wrapping the unresolved count and spinning. - Carry the reservation ID in the BackendReceive event instead of request state. - Pin the wait round-up with a unit test and document the unused rtt_ms diagonal. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Signed-off-by: Barry Greengus <bgreengus@nvidia.com>
The parity config used retired queue-mismatch thresholds and published Pylon statistics only on heartbeats. Use the current 10,000 ms / 4.0 queue-mismatch defaults and the 10 ms change-driven stats coalescing. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Signed-off-by: Barry Greengus <bgreengus@nvidia.com>
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Signed-off-by: Barry Greengus <bgreengus@nvidia.com>
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Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Signed-off-by: Barry Greengus <bgreengus@nvidia.com>
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No P0/P1 findings. Reviewed simulator routing and reservation parity, Pylon bookkeeping, workload generation, validation, metrics, and production API exports. Isolated exact-head cargo test --locked -p stargate-routing-sim passed all 17 tests. Current GitHub checks pass. No live-cluster validation.
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🎉 This PR is included in src/libraries/rust/stargate/v0.26.0 🎉 The release is available on GitHub release Your semantic-release bot 📦🚀 |
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TL;DR
Adds
stargate-routing-sim, a discrete-event simulator that drives the production Stargate load balancers in virtual time against a modeled fleet of Pylon and MockDynamo backends. A full policy sweep (several algorithms, rates and seeds) on a 20-backend, five-region topology takes seconds to minutes instead of cluster hours.Stacked on #2286, which provides the
mock-enginecrate the simulated backends run. #1002 (maximum input TPS for Pulsar) and #2288 (Pulsar-WaW) have merged; the remaining stack is #2286, then this PR, then #2321.Additional Details (optional for docs, build, test, refactor, ci, chore, style, and revert PRs)
Why: each cluster data point costs about 15 minutes of serialized multi-region traffic. Comparing load-balancing policies and their settings across workload regimes needs thousands of runs, so the search has to happen in simulation, with cluster runs validating selected points.
What the simulator models:
Stargate:
LoadBalancerper Stargate, called through the public API. Nothing is reimplemented. Load balancers read virtual time through a backdatedreceived_at.Pylon:
last_mean_input_tpsandmax_input_tps.Engine: the
mock-enginecrate that MockDynamo also runs. Each backend is a deployment of N GPU workers with:GPU counts can differ per backend.
Network: an inter-region RTT matrix.
Clients:
Output: goodput, SLO attainment, TTFT and E2E percentiles, cache reuse, failures by kind, retries, cross-region share, and a per-backend breakdown.
Usage:
Limitations (also in the crate README):
max_input_work_secondsadmission,consider_kv_free_tokens(rejected at validation), and priorities are not modeled. Simulated Pylons publish no KV-cache stats.pylon.stats_update_coalesce_ms, Pylons publish only on the heartbeat; production Pylons also publish on request state changes, every 10 ms by default.For the Reviewer
crates/stargate-routing-sim/src/sim.rs: the event loop and the mirrored proxy routing behavior. Check it againststargate/src/http_proxy/run.rs,routing.rsandrouting_state/reservations.rs.crates/stargate-routing-sim/src/backend.rs: Pylon bookkeeping and the fallback throughput window. Check it againstpylon-lib/src/queue_admission.rsandstats/aggregator.rs.crates/stargate-routing-sim/src/workload.rs: fixed and growing session generation.For QA (optional for docs, build, test, refactor, ci, chore, style, and revert PRs)
cargo test --locked -p stargate-routing-sim: 13 tests pass. They include end-to-end fixed, growing, and short-timeout growing-session runs over three policies, which check that every measured request has one outcome, that timeouts and turn retries occur when expected, and (through debug assertions) that every request resolves and every simulated Pylon and engine ends empty. Config validation rejects values that would hang or misroute.cargo test --locked -p mock-engine: 18 tests pass.cargo clippy --locked -p stargate-routing-sim --all-targets -- -D warningsandcargo fmt --all -- --check: clean.bazel test //src/libraries/rust/stargate/crates/stargate-routing-sim/... //src/libraries/rust/stargate/crates/mock-engine/...: 2 of 2 targets pass.No new third-party dependencies.
Issues
Relates to #2222
Related Pull Requests
mock-engine.Checklist
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