[RFC][Core][Model] Voxtral realtime: unbounded-duration streaming via RoPE re-anchoring (experimental, default-off) - #45833
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Both points from the #45022 review look addressed here — thanks for the thorough follow-up.
test_voxtral_realtime_reanchor_parity is exactly the coverage I was after: a real attention forward + re-anchor against a re-anchor-OFF reference asserting token-for-token parity, not just the algebra. Proving the path fired via "a session can't emit more than max_model_len output tokens unless its clock was re-anchored down" is a clean way to make it CI-checkable without scraping the subprocess scheduler log.
And the up-front startup validation — rejecting a non-128 decoder head_dim and guarding the pool derivation so it can't silently fall to 1 — is the right fix for the head_size/pool coupling: it fails loud at init instead of silently mis-rotating encoder keys. Nothing further from me on those two.
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Rebased on #45022. This is the unbounded re-anchoring RFC @ywang96 wanted to leave to Mistral. @patrickvonplaten @juliendenize @andylolu2 can you look at the design? Default-off, gated on |
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Rebased on top of #45022 (itself rebased on main today), conflicts gone. No functional change; also dropped a stale README reference to an uncommitted results directory in the benchmark harness. Two related items filed today, both about the realtime path this RFC introduces: #47614 documents a self-sustained blank-token rut that mutes live sessions for minutes (deterministic reproducer and logit-margin measurements included), and #47615 (draft, stacked on this branch) adds an opt-in, default-off mitigation. Worth a look from the Mistral folks alongside the RFC design review, since the rut is a property of the temperature-0 re-feeding loop. |
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…nk, stop the stream at max_model_len Signed-off-by: Damien Laine <damien.laine@gmail.com>
…sconnect Signed-off-by: Damien Laine <damien.laine@gmail.com>
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…ep the encoder cache size A paused streaming session keeps its last chunk in the encoder cache until it resumes. Sizing the cache to one chunk deadlocks a handful of concurrent sessions when max_num_batched_tokens is small. Signed-off-by: Damien Laine <damien.laine@gmail.com>
… RoPE re-anchoring Before a streaming session reaches max_model_len, the scheduler shifts its positions down by D and the V1 worker rotates the cached keys by R(-D). Default-off behind --enable-realtime-unbounded; the realtime buffer does not cap the stream at max_model_len when it is set. Re-anchoring is V1-runner only: the flag falls back to V1 and rejects VLLM_USE_V2_MODEL_RUNNER=1. Signed-off-by: Damien Laine <damien.laine@gmail.com>
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[RFC, experimental, default-off] Unbounded session duration for sliding-window realtime models (Voxtral) via RoPE re-anchoring, behind
--enable-realtime-unbounded.Stacked on #45022. RFC-only diff:
voxtral-realtime-unbounded...voxtral-realtime-rfcUpdate 2026-10-05
Rebased on the reworked #45022, which is now Voxtral-only (no scheduler changes). The RFC diff is only the re-anchor now. With the flag on, the realtime buffer no longer stops the stream at
max_model_len(serving.pypassesunbounded=True).Re-checked on RTX 4090: parity test passes, and over websocket a 120 s stream on
--max-model-len 1024re-anchors 3 times and finishes cleanly.In production at LinTO for months (Wikimania 2026 live captions: 6 streams × 6 translation languages on one L40S, multi-hour sessions, flat VRAM).
How it works
Session length is capped by the position counter (
max_model_len), not by memory: the sliding window already bounds KV. RoPE scores only depend onm - n, and a query only sees keys in(m-W, m], so shifting every live position down byDchanges nothing. Before the clock reaches the cap, the scheduler drops the head of the session and the worker re-rotates the cached K in place byR(-D). Each key is rotated at most once while in the window.Scope: sliding-window, non-fp8 KV, no pinned attention sink (see #51948 for why sinks don't fit). Startup guards reject fp8 KV, prefix caching, non-CUDA, scaled RoPE,
rope_theta != 1e6, missing head-room, and unexpected head dims / audio pool factor.Update 2026-09-30
Rebased on main (merge commit). Changes:
VLLM_USE_V2_MODEL_RUNNER=1. V2 port is the follow-up if the design is accepted.[B, H, N, 2*head_size]([6/N][KV-Cache Layout Refactor] Standardize KV cache layout #51718).head_sizeis read from the layer instead of the tensor (the tensor now reports 256 for the decoder and 128 for the 64-dim encoder), K is[..., :head_size], shape asserted.Dneedsclock - window >= 128. No impact at mml 8192 / margin 4096. The parity test now uses window 128. A startup guard for this is still TODO.Validation
tests/v1/worker/test_reanchor_rotary.py(CPU):R(-D)identity, in-window score preservation.test_voxtral_realtime_reanchor_parity(CUDA): re-anchor fires, output identical to the re-anchor-off reference. Passes on RTX 4090, current main.Config:
AI-assisted; reviewed and validated by me.