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fix: price vLLM mixed replay passes as one forward pass - #612
vLLM replay priced a pass that computes both prefill and decode work as a prefill pass plus a full, separate decode pass (predict_prefill_duration, then emit_ready_tokens → predict_decode_time), so the per-pass cost both phases share was paid twice. The perf model already composes such a pass as one forward for whole-model FPM telemetry: prefill(np, Tp, KVp) + max(0, decode(B, KV) − decode_pass_baseline(B, KV)) in rank_latency_ms.
TimingModel::predict_mixed_pass_ms(prefill, …) lets a timing provider price a pass that computes prefill (PrefillTotals) and a decode batch as one forward, returning its prefill and decode parts (MixedPassMs). The default None keeps the prefill and a separate decode pass.
The vLLM/TRT-LLM core prices a pass's forward once its decode work is known, in the ordinary and the speculative path, so a composed pass prices its prefill once.
The ais provider answers for whole-model FPM interpolation with the prefill plus the decode term of rank_latency_ms, now Engine::fpm_decode_term_ms and shared by both. A tuned snapshot (feat: save and restore FPM model state through best_available #607) applies the online correction of that mixed iteration to both parts, so a mixed replay pass costs what estimate_forward_pass_time_ms() returns for it; prefill-only and decode-only passes keep their own corrections. Captured diagnostics record the share as its own decode-phase FPM evidence and key records by their correction.
Unchanged: polynomial and fixed timing, operation-level AIC timing, measured SD-round FPM profiles, MTP drafts, and every prefill-only or decode-only pass. SGLang runs no mixed pass.
Review map
Risk level: medium
Start with: crates/core/src/engine/scheduler/vllm/core.rs (forward_time, ForwardTime, the emit_ready_tokens returns), then crates/core/src/python.rs (predict_mixed_pass_ms, mixed_correction, record_fpm_estimate) and crates/core/src/perfmodel/engine/runtime.rs (fpm_decode_term_ms, fpm_mixed_decode_term_ms).
Public or serialized contract changed: additive. TimingModel::predict_mixed_pass_ms has a default, and aisimulate_core::engine::{PrefillTotals, MixedPassMs} are new; no existing public struct gains a field, so Dynamo's DynamoPerfTimingModel compiles and prices as before.
Compatibility or rollback concern: vLLM and TRT-LLM replays with FPM interpolation timing price mixed passes lower, so their reports change. Replays of a tuned snapshot correct a mixed pass as a mixed iteration instead of correcting its prefill and decode passes separately; docs/perf-model/configuration.md now says so.
Evidence
Tests (Linux x86 VM, Rust 1.96.1, commit 0f1cd66): cargo fmt --all -- --check; cargo test --workspace (core 2,359 passed) and cargo test --workspace --features embed-python,replay-bench with AIC_REQUIRE_EMBEDDED_ROUND_TRIP=1 (core 2,447 passed) pass with no failures. On 1944d8c85, whose non-test code differs only in comments, the perfmodel parity suites as CI runs them pass with goldens unchanged (test_engine_step_parity.py 304, test_compile_engine_parity.py 85), native prediction sentinels report 16 cases, 0 failures, and cargo test --manifest-path crates/tests/public-api/Cargo.toml passes (21).
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Codex reviewed commit: not run; independent Claude reviews of 9f21f4b8b and of 1944d8c85 (the tuned-model correction) found no high or medium issues; 0f1cd66 adds that review's low-severity comment, doc and validation-test fixes.
New tests: mixed_pass_timing (vLLM, TRT-LLM, a provider without composition, MTP; a composed pass prices no separate prefill), fpm_mixed_decode_term_completes_the_one_pass_estimate (SD-round profiles and operation graphs define no share), native_fpm_mixed_pass_is_the_one_pass_estimate (provider path, zero share, captured evidence), tuned_model_corrects_a_mixed_pass_as_one_mixed_iteration (tuned snapshot, with and without capture).
Expected-value derivation: in the native provider test, the prefill row prices 8 new tokens at 10 ms; decode at 8 past KV tokens lies halfway between the 4- and 12-token rows (3 ms); the one-request pass baseline is the smallest-KV row (2 ms). The share is therefore 1 ms and the pass 11 ms. The tuned test observes that prefill alone at 1.5x (15 ms) and the mixed iteration at 1.25x (13.75 ms), so the mixed pass costs 12.5 + 1.25 ms, equal to estimate_forward_pass_time_ms() of that iteration, while the prefill alone stays at 15 ms.
Exp1 reproduction (MiniMax-M3-NVFP4, TP4 B200, 18 configs, 10,220 requests): main plus the experiment's composition patch and this branch plus the same lookahead patch are identical request for request (measured on the pre-rebase commit 04184809a). After merging main, the tuned-model correction leaves these untuned replays identical request for request (10,220 of 10,220, merge commit ca8f454 against 1944d8c85).
Per-pass accuracy on GT mixed passes (median signed error): double-priced +5.9% to +6.2% on 8k and +4.7% on 1k; one-pass −3.6% to −3.9% on 8k and −7.6% to −7.9% on 1k. The double count happened to offset a mixed-pass cost the FPM rows do not contain (see provenance).
End to end on Exp1 (5 points, TTFT mean / p50 / p90 · TPOT mean · throughput MAPE %), main → this PR: G8k 5.7/13.5/16.4 · 1.9 · 1.9 → 8.9/18.1/19.6 · 1.5 · 1.8; G1k 9.7/8.1/16.4 · 1.3 · 1.4 → 14.5/14.1/21.4 · 3.9 · 4.4. TTFT is under-predicted until the follow-up async-scheduling PR delays admission.
Cost: one more FPM lookup (the decode baseline) per mixed pass: 1k c256 does 11,814 lookups on main and 13,903 here; 8k c64 10,302 and 10,874. Native wall_time_ms, release builds, five paired alternating runs: 1k c256 854.6 → 868.8 ms (median ratio 1.020, range 0.995–1.046), 8k c64 211.3 → 216.3 ms (1.011, 0.901–1.037), 1k c1 control 21.3 → 21.3 ms (1.008); within run-to-run noise.
Modeling or data provenance
The composition is rank_latency_ms, mirroring _get_fpm_mix_step_latency.
Mixed passes remain under-priced: in GT a mixed pass costs about 8–10 ms more than its prefill-only or decode-only parts, flat in the decode batch, which pure prefill and decode rows cannot see. Pricing the prefill lookup at prefill plus decode tokens (the static fpm_mixed_step_components convention) is not better overall: 1k bulk −7.5% → −8.9%, small chunks −42.6% → −24.8%, and 6% of 8k mixed passes become unpriceable (single prefills above the collected 8,192 tokens).
Tracking
Closes: N/A
Related PRs or issues: vLLM async-scheduling admission follows as a stacked PR.
vLLM replay priced a pass with prefill and decode work as a prefill pass
plus a full, separate decode pass, paying the shared per-pass cost twice.
TimingModel::predict_mixed_decode_ms lets a timing provider return the
decode share of a pass that also computes prefill, and the vLLM/TRT-LLM
core passes the prefill totals it priced. The AIC provider answers for
whole-model FPM with the decode term of rank_latency_ms, now shared as
Engine::fpm_decode_term_ms, so a mixed pass costs the perf model's
one-pass estimate. Other providers keep the separate decode pass.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Yongming Ding <yongmingd@nvidia.com>
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Risk: Medium. The three areas for human review are the public TimingModel contract and fallback behavior, FPM eligibility and decode-share calculations, and vLLM scheduling paths that provide prefill totals.
Changed behavior and contracts
The public API adds PrefillTotals and the optional TimingModel::predict_mixed_decode_ms hook. The hook defaults to None.
PerfModel::predict_mixed_decode_time uses a provider estimate when available and valid. Otherwise, it uses decode-only pricing.
vLLM passes prefill totals into decode pricing for ordinary and speculative mixed passes.
The built-in ais provider supplies a mixed decode share for eligible whole-model FPM timing. Operation-level timing and unsupported FPM modes use separate-pass pricing, according to the supplied change summary.
Evidence and limitations
The latest repository search confirms the API, vLLM mixed-decode call path, FPM mixed-decode methods, and mixed-pass tests exist.
The PR objectives report passing formatting, workspace tests, parity suites, and native prediction sentinels. These results are author-reported; independent test output was not supplied.
The objectives report changed results for FPM-interpolated replays and under-predicted TTFT pending a follow-up scheduling change.
Current review findings were not supplied. Review severity counts are unavailable.
Technical quality and merge readiness
The supplied summaries describe tests for mixed-pass estimates and one-pass recomposition. The available evidence does not independently verify test results or establish coverage of every compatibility risk.
Technical quality and merge readiness are not established by the supplied evidence. Independent test output and current review findings are unavailable.
The change adds optional mixed-decode estimates to timing providers and FPM models. The vLLM scheduler uses these estimates for decode work sharing a pass with prefill, with decode-only pricing as the fallback.
Changes: Mixed-Pass Timing
Layer / File(s)
Summary
Timing contract and fallback crates/core/src/engine/timing.rs, crates/core/src/engine/mod.rs, crates/core/src/engine/common/perf_model.rs
Adds PrefillTotals and an optional TimingModel mixed-decode hook. PerfModel validates estimates and falls back to decode-only prediction when none is supplied.
Adds FPM mixed-decode queries and shared rank-level pricing. Mixed pricing subtracts the decode-pass baseline, clamps the result to zero, and records lookup evidence.
Adds mixed-decode estimates for whole-model FPM timing, checked decode coordinates, and separate evidence phases for prefill, standalone decode, and mixed decode.
ai-dynamo/aisimulate#585: Adds the total-based FPM mixed-decode queries and shared decode-term calculations used by this change.
Merge Risk: Minimal · up to 22f0d
No unresolved merge-blocking risk was identified in the mixed-pass pricing change.
Pre-merge checks: 6 · 1 · 1
Failed checks: 1 warning · 1 inconclusive
Check name
Status
Explanation
Resolution
Cross-Layer Contract
Mixed-pass Rust/Python wiring is present and the new scheduler, FPM, and provider paths have tests. However, the changed documentation is stale against the provider schema. `docs/replay/api/rust.md:42…
Make the provider contract consistent. Prefer changing the new documentation references from ais to the accepted identifier aic. If ais is intended as the public identifier, update every parser, CLI/config serializer, downstream consu…
Review Evidence
The visible description names commands and results (cargo fmt, workspace tests, feature-mode tests, parity suites, and numerical sentinels) and states boundary coverage such as zero input, unsupport…
Provide the complete PR description, including the remainder of the Evidence section. Confirm the execution source for each result: local VM, fake runner, parity suite, or production run. Confirm that no inactive nested workflow is presente…
Passed checks: 6 passed
Check name
Status
Explanation
Title check
The title precisely describes the behavioral change: vLLM mixed replay passes are priced as one forward pass.
Linked Issues check
Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check
Check skipped because no linked issues were found for this pull request.
Modeling And Data Evidence
The PR supplies reproducible model evidence and before/after comparison. runtime.rs adds deterministic FPM rows and asserts that prefill plus max(0, decode - baseline) equals the one-pass estimate…
Compatibility Boundaries
No compatibility-boundary failure is introduced. TimingModel::predict_mixed_decode_ms has a default None implementation at crates/core/src/engine/timing.rs:805-822, so existing Rust providers re…
Description check
The description includes all required template sections and provides detailed behavior, review risks, compatibility impact, test commands, numerical derivations, performance evidence, modeling provena…
Full details: Modeling And Data Evidence
Explanation
The PR supplies reproducible model evidence and before/after comparison. runtime.rs adds deterministic FPM rows and asserts that prefill plus max(0, decode - baseline) equals the one-pass estimate, while decode-only pricing remains full-pass pricing (lines 5449-5526). python.rs repeats this with explicit rows and an explained 10 ms + 1 ms = 11 ms derivation, including zero-share evidence retention (the added test starts at line 5531). vLLM tests cover vLLM, TRT-LLM, fallback pricing, and speculative decoding with explicit expected durations (lines 925-975). The PR description also reports provenance and held-out before/after results for 18 configurations and 10,220 requests, including mixed-pass signed-error medians. The changed-file inventory contains no unexplained golden or binary refresh.
Full details: Compatibility Boundaries
Explanation
No compatibility-boundary failure is introduced. TimingModel::predict_mixed_decode_ms has a default None implementation at crates/core/src/engine/timing.rs:805-822, so existing Rust providers remain source-compatible; Dynamo's DynamoPerfTimingModel still implements only the required prefill/decode methods (ai-dynamo/dynamo, commit 45e30e07a4f4cef37ab7bfa739f7bee0c89b3057, lib/mocker/src/engine_adapter.rs:144-169). PrefillTotals is an additive Rust type re-exported from engine; it is not serialized or added to the Python binding. The PR changes no manifests, schemas, or binding files. The crate and wheel versions remain synchronized at 0.13.0, and maturin still builds the existing aisimulate-core crate into the existing wheel (Cargo.toml, crates/core/Cargo.toml, python/aisimulate/pyproject.toml). The diff adds no Dynamo dependency or artifact.
Full details: Description check
Explanation
The description includes all required template sections and provides detailed behavior, review risks, compatibility impact, test commands, numerical derivations, performance evidence, modeling provenance, and tracking information. Some CI and review-commit fields are blank, and the documented API names should be reconciled with the implementation summary, but the description is substantially complete.
Full details: Cross-Layer Contract
Explanation
Mixed-pass Rust/Python wiring is present and the new scheduler, FPM, and provider paths have tests. However, the changed documentation is stale against the provider schema. docs/replay/api/rust.md:42-49 names the built-in provider ais, while crates/core/src/python.rs:1630-1639 accepts only provider == "aic"; the same accepted identifier is enforced in the encoder path. A user following the changed documentation cannot configure the documented provider. The linked Dynamo consumer also uses an explicit TimingModel implementation at lib/mocker/src/engine_adapter.rs:148-169 (repository ai-dynamo/dynamo, commit 45e30e07a4f4cef37ab7bfa739f7bee0c89b3057), so the additive trait default preserves that consumer but does not resolve the provider-name mismatch.
Resolution
Make the provider contract consistent. Prefer changing the new documentation references from ais to the accepted identifier aic. If ais is intended as the public identifier, update every parser, CLI/config serializer, downstream consumer, test fixture, and compatibility document together. Add a configuration round-trip test that verifies the documented provider identifier is accepted.
Full details: Review Evidence
Explanation
The visible description names commands and results (cargo fmt, workspace tests, feature-mode tests, parity suites, and numerical sentinels) and states boundary coverage such as zero input, unsupported engines, no mixed estimate, and zero shares. The available text is truncated during the evidence section at “End to end on Exp1”, so I cannot verify the required distinction between local, fake-runner, parity, and production evidence or rule out an omitted claim that an inactive nested workflow was hosted CI evidence. The repository policy also requires those evidence categories to remain distinct (REVIEW.md:128-140).
Resolution
Provide the complete PR description, including the remainder of the Evidence section. Confirm the execution source for each result: local VM, fake runner, parity suite, or production run. Confirm that no inactive nested workflow is presented as hosted CI evidence.
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Review comments at @crates/core/src/python.rs:
- Around line 1127-1137: Update record_fpm_estimate to retain zero-latency
estimates when their ranks contain executed queries, while continuing to skip
estimates with no queries. Add a regression test for a baseline lookup equal to
or greater than the decode lookup and assert the MixedDecode evidence record has
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Enforce the single-oracle and golden-diff rules in python/aisimulate/.claude/rules/rust-core/parity.md.
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Review scheduler state transitions and event ordering, including cancel, preempt, drain, retry, duplicate, empty, and terminal paths.
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crates/core/src/engine/common/perf_model.rs
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crates/core/src/engine/mod.rs
docs/perf-model/methods/whole-forward.md
crates/core/src/engine/timing.rs
crates/core/src/engine/common/perf_model.rs
crates/core/src/perfmodel/fpm/model.rs
docs/replay/api/rust.md
crates/core/src/engine/scheduler/vllm/tests.rs
crates/core/src/perfmodel/engine/runtime.rs
crates/core/src/engine/scheduler/vllm/core.rs
crates/core/src/python.rs
Applicability reference: crates/core/src/engine/scheduler/vllm/AGENTS.md: CLAUDE.md Source excerpt: Do not recreate a separate TRT-LLM scheduler or scatter `EngineType` checks through `core.rs`; extend `SchedulingPolicy` and `policy.rs`.
Applicability reference: crates/core/src/engine/scheduler/vllm/AGENTS.md: CLAUDE.md Source excerpt: vLLM admits based on the current known sequence and permits decode-time preemption.
Source excerpt: Keep run logs, investigation notes, and benchmark results out of `docs/`; measured evidence belongs under `benchmarks/evidence/`.
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crates/core/src/engine/mod.rs
docs/perf-model/methods/whole-forward.md
crates/core/src/engine/timing.rs
crates/core/src/engine/common/perf_model.rs
crates/core/src/perfmodel/fpm/model.rs
docs/replay/api/rust.md
crates/core/src/engine/scheduler/vllm/tests.rs
crates/core/src/perfmodel/engine/runtime.rs
crates/core/src/engine/scheduler/vllm/core.rs
crates/core/src/python.rs
Source excerpt: Binary parquet changes require a machine-readable summary of keys, shapes, units, row counts, coverage, and anomalies plus proof that a real consumer reaches the new data.
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Files:
crates/core/src/engine/mod.rs
docs/perf-model/methods/whole-forward.md
crates/core/src/engine/timing.rs
crates/core/src/engine/common/perf_model.rs
crates/core/src/perfmodel/fpm/model.rs
docs/replay/api/rust.md
crates/core/src/engine/scheduler/vllm/tests.rs
crates/core/src/perfmodel/engine/runtime.rs
crates/core/src/engine/scheduler/vllm/core.rs
crates/core/src/python.rs
Applicability reference: crates/core/src/engine/scheduler/vllm/AGENTS.md: CLAUDE.md Source excerpt: `core.rs` owns common queue mechanics, KV allocation, state transitions, completion, and event emission.
DynamoPerfTimingModel implements only prefill and decode timing; the new default predict_mixed_decode_ms -> None preserves this adapter and therefore keeps separate decode pricing. [::ai-dynamo/dynamo::lib/mocker/src/engine_adapter.rs:148-173]
External NPZ/AIS providers still use the existing decode path, while polynomial/fixed timing is owned by AISimulate’s engine. [::ai-dynamo/dynamo::lib/mocker/src/common/perf_model.rs:269-306]
Dynamo pins exact AISimulate Rust and Python versions, so the new hook requires coordinated package/version publication before this consumer can use it. [::ai-dynamo/dynamo::Cargo.toml:55-56] [::ai-dynamo/dynamo::pyproject.toml:17]
ai-dynamo/aiconfigurator
The frozen FPM reference uses token-based mixed-pass detection (sum_prefill_tokens > 0), avoiding treating fully prefix-cached decode work as prefill. [::ai-dynamo/aiconfigurator::aic-core/rust/aiconfigurator-core/src/engine/runtime.rs:1455-1464]
Mixed FPM timing composes prefill with marginal decode and queries exact iteration totals rather than per-request averages, matching the new PrefillTotals boundary. [::ai-dynamo/aiconfigurator::aic-core/rust/aiconfigurator-core/src/engine/runtime.rs:1466-1477] [::ai-dynamo/aiconfigurator::docs/fpm/aic-fpm-rust-port-design-20260802.md:143-157]
The frozen reference explicitly distinguishes mixed, decode-only, and prefill-only behavior; its legacy predict_prefill_latency/predict_decode_latency APIs remain separate. [::ai-dynamo/aiconfigurator::aic-core/src/aiconfigurator_core/_aiconfigurator_core.pyi:25-35]
Additional comments: 10
crates/core/src/engine/timing.rs: 1
746-754: LGTM!
Also applies to: 805-823
crates/core/src/engine/mod.rs: 1
58-62: LGTM!
crates/core/src/engine/common/perf_model.rs: 1
12-12: LGTM!
Also applies to: 163-203
crates/core/src/perfmodel/engine/runtime.rs: 1
1325-1366: LGTM!
Also applies to: 2810-2819, 2917-2996, 5445-5528
crates/core/src/perfmodel/fpm/model.rs: 1
1337-1378: LGTM!
crates/core/src/python.rs: 1
1105-1145: LGTM!
Also applies to: 1216-1232, 5524-5614
crates/core/src/engine/scheduler/vllm/core.rs: 1
2280-2286: LGTM!
Also applies to: 2925-2955, 3076-3076, 3258-3258, 3410-3441
A mixed decode share is max(0, decode - baseline) and is zero when the
decode row is its own pass baseline. Both lookups still ran, but capture
dropped every non-positive estimate, so the detailed FPM evidence lost
the record and its invocation count. Keep estimates whose baseline was
looked up; empty work still records nothing.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Yongming Ding <yongmingd@nvidia.com>
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Review comments at @docs/replay/api/rust.md:
- Line 43: Update the documentation for the `ais` provider to state that it
returns the share only when whole-model FPM interpolation is enabled and a mixed
estimate is available; otherwise, replay uses separate decode pricing.
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Source excerpt: Keep run logs, investigation notes, and benchmark results out of `docs/`; measured evidence belongs under `benchmarks/evidence/`.
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Source excerpt: Binary parquet changes require a machine-readable summary of keys, shapes, units, row counts, coverage, and anomalies plus proof that a real consumer reaches the new data.
DynamoPerfTimingModel implements only prefill and standalone decode methods; the new default mixed hook will therefore retain separate decode-pass pricing for Dynamo’s adapter. [::ai-dynamo/dynamo::lib/mocker/src/engine_adapter.rs:148-173]
Dynamo pins AISimulate Rust and Python packages to exact versions, so consuming the new public API requires coordinated package publication. [::ai-dynamo/dynamo::Cargo.toml:55-56] [::ai-dynamo/dynamo::pyproject.toml:17]
ai-dynamo/aiconfigurator
FPM dispatch is token-based: sum_prefill_tokens > 0 is required to classify work as prefill, preventing fully prefix-cached decode-only work from entering mixed pricing. [::ai-dynamo/aiconfigurator::aic-core/rust/aiconfigurator-core/src/engine/runtime.rs:1459-1470]
The reference FPM implementation composes mixed latency from prefill plus marginal decode using telemetry totals, matching the new PrefillTotals contract. [::ai-dynamo/aiconfigurator::aic-core/rust/aiconfigurator-core/src/engine/runtime.rs:1470-1486]
Its public API retains separate prefill/decode methods alongside mixed_step_latency, supporting the additive compatibility approach in this PR. [::ai-dynamo/aiconfigurator::aic-core/src/aiconfigurator_core/_aiconfigurator_core.pyi:25-35]
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Review comments at @docs/replay/api/rust.md:
- Around line 43-44: Update the `ais` provider documentation to state that it
returns a decode share only when whole-model FPM interpolation is enabled and a
mixed estimate is available; otherwise, replay uses a separate decode pass.
Preserve the existing exclusions for operation-level timing, measured SD-round
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Files:
docs/replay/api/rust.md
Source excerpt: Keep run logs, investigation notes, and benchmark results out of `docs/`; measured evidence belongs under `benchmarks/evidence/`.
CodeRabbit inference engine (AGENTS.md)
Files:
docs/replay/api/rust.md
Source excerpt: Binary parquet changes require a machine-readable summary of keys, shapes, units, row counts, coverage, and anomalies plus proof that a real consumer reaches the new data.
CodeRabbit inference engine (REVIEW.md)
Files:
docs/replay/api/rust.md
Learnings: 1
Common learnings
Learnt from: CR
Repo: ai-dynamo/aisimulate PR: 0
File: AGENTS.md:0-0
Timestamp: 2026-10-20T16:50:41.000Z
Learning: Source excerpt:
# AGENTS
## Pull request titles
- Use `<type>: <short description>` for every AISimulate PR title.
A second TimingModel implementation, the test-only PromptLengthTiming, also implements only prefill and standalone decode methods; it will rely on the new default mixed-timing behavior. [::ai-dynamo/dynamo::lib/mocker/src/generalized_live.rs:839-858]
AISimulate Rust and Python dependencies remain exact-version pinned, so publication/update coordination is required. [::ai-dynamo/dynamo::Cargo.toml:55-56] [::ai-dynamo/dynamo::pyproject.toml:15-17]
ai-dynamo/aiconfigurator
The reference dispatch distinguishes actual new prefill tokens from prefix-cached metadata: sum_prefill_tokens == 0 is treated as decode-only. [::ai-dynamo/aiconfigurator::aic-core/rust/aiconfigurator-core/src/engine/runtime.rs:1459-1464]
For mixed FPM work, it queries prefill using aggregate request/token/KV totals, then adds only decode latency above the decode baseline. [::ai-dynamo/aiconfigurator::aic-core/rust/aiconfigurator-core/src/engine/runtime.rs:1469-1509]
Metrics validation permits prefill KV-token totals only when a prefill request count exists, while the dispatch decision still depends on fresh prefill-token totals. [::ai-dynamo/aiconfigurator::aic-core/rust/aiconfigurator-core/src/fpm/metrics.rs:108-123]
Resolve crates/core/src/python.rs against #607's online corrections: keep
main's corrected prefill and decode paths with FpmEvidencePhase keys and
reuse total_past_kv_tokens in the mixed decode share.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Yongming Ding <yongmingd@nvidia.com>
#607 corrects replay timing per phase. A vLLM or TensorRT-LLM pass that
computes prefill and decode is one forward, which a tuned model corrects as a
mixed iteration, so the pass must cost what estimate_forward_pass_time_ms()
returns for that iteration. Schedulers now price such a pass once its decode
work is known: TimingModel::predict_mixed_pass_ms returns the prefill and
decode parts of one forward, and the ais provider applies the mixed
iteration's correction to both. Captured FPM evidence keys records by their
correction, since the same prefill totals are corrected differently alone and
in a mixed pass. Passes without both kinds of work, and providers without the
composition, are priced as before.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Yongming Ding <yongmingd@nvidia.com>
Signed-off-by: Yongming Ding <yongmingd@nvidia.com>
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
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Why and what changed
vLLM replay priced a pass that computes both prefill and decode work as a prefill pass plus a full, separate decode pass (
predict_prefill_duration, thenemit_ready_tokens→predict_decode_time), so the per-pass cost both phases share was paid twice. The perf model already composes such a pass as one forward for whole-model FPM telemetry:prefill(np, Tp, KVp) + max(0, decode(B, KV) − decode_pass_baseline(B, KV))inrank_latency_ms.TimingModel::predict_mixed_pass_ms(prefill, …)lets a timing provider price a pass that computesprefill(PrefillTotals) and a decode batch as one forward, returning its prefill and decode parts (MixedPassMs). The defaultNonekeeps the prefill and a separate decode pass.aisprovider answers for whole-model FPM interpolation with the prefill plus the decode term ofrank_latency_ms, nowEngine::fpm_decode_term_msand shared by both. A tuned snapshot (feat: save and restore FPM model state through best_available #607) applies the online correction of that mixed iteration to both parts, so a mixed replay pass costs whatestimate_forward_pass_time_ms()returns for it; prefill-only and decode-only passes keep their own corrections. Captured diagnostics record the share as its own decode-phase FPM evidence and key records by their correction.Review map
crates/core/src/engine/scheduler/vllm/core.rs(forward_time,ForwardTime, theemit_ready_tokensreturns), thencrates/core/src/python.rs(predict_mixed_pass_ms,mixed_correction,record_fpm_estimate) andcrates/core/src/perfmodel/engine/runtime.rs(fpm_decode_term_ms,fpm_mixed_decode_term_ms).TimingModel::predict_mixed_pass_mshas a default, andaisimulate_core::engine::{PrefillTotals, MixedPassMs}are new; no existing public struct gains a field, so Dynamo'sDynamoPerfTimingModelcompiles and prices as before.docs/perf-model/configuration.mdnow says so.Evidence
cargo fmt --all -- --check;cargo test --workspace(core 2,359 passed) andcargo test --workspace --features embed-python,replay-benchwithAIC_REQUIRE_EMBEDDED_ROUND_TRIP=1(core 2,447 passed) pass with no failures. On 1944d8c85, whose non-test code differs only in comments, the perfmodel parity suites as CI runs them pass with goldens unchanged (test_engine_step_parity.py304,test_compile_engine_parity.py85), native prediction sentinels report 16 cases, 0 failures, andcargo test --manifest-path crates/tests/public-api/Cargo.tomlpasses (21).mixed_pass_timing(vLLM, TRT-LLM, a provider without composition, MTP; a composed pass prices no separate prefill),fpm_mixed_decode_term_completes_the_one_pass_estimate(SD-round profiles and operation graphs define no share),native_fpm_mixed_pass_is_the_one_pass_estimate(provider path, zero share, captured evidence),tuned_model_corrects_a_mixed_pass_as_one_mixed_iteration(tuned snapshot, with and without capture).estimate_forward_pass_time_ms()of that iteration, while the prefill alone stays at 15 ms.wall_time_ms, release builds, five paired alternating runs: 1k c256 854.6 → 868.8 ms (median ratio 1.020, range 0.995–1.046), 8k c64 211.3 → 216.3 ms (1.011, 0.901–1.037), 1k c1 control 21.3 → 21.3 ms (1.008); within run-to-run noise.Modeling or data provenance
rank_latency_ms, mirroring_get_fpm_mix_step_latency.fpm_mixed_step_componentsconvention) is not better overall: 1k bulk −7.5% → −8.9%, small chunks −42.6% → −24.8%, and 6% of 8k mixed passes become unpriceable (single prefills above the collected 8,192 tokens).Tracking
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