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feat(disagg): broaden lever A to full sequence incl cached prefix (high cache-hit)

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The premise holds at realistic context: at ~8k tokens + high cache-hit the KV
transfer is ~30% of TTFT (712ms), sequential after the forward. Lever A was scoped
to prefix==0 so it never activated there. Broaden it to cover the FULL sequence
(cached prefix + new tokens): the per-layer backup hook fires after each layer's
full processing, so the HiCache-loaded prefix KV and forward-written new KV are both
final — transferring all of layer L's pages then overlaps the dominant prefix
transfer with the forward. Add a sonnet-bench verify mode for output-equality.
Gated by the flag; correctness verified next.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
This commit is contained in:
孙远航
2026-06-07 04:30:33 +00:00
parent 76dc60a1d0
commit 5791684864
1 changed files with 6 additions and 4 deletions
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10
python/sglang/srt/disaggregation/prefill.py
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@@ -666,10 +666,12 @@ class SchedulerDisaggregationPrefillMixin:
continue
if getattr(req, "is_chunked", 0) != 0 or getattr(req, "start_send_idx", 0) != 0:
continue # chunked / partially-sent: this forward isn't the full range
prefix = getattr(req, "prefix_indices", None)
# NB: prefix_indices is a tensor — never use `or`/truthiness on it.
if prefix is not None and len(prefix) != 0:
continue # cached prefix is HiCache-loaded, not forward-written -> lever B
# Cover the FULL sequence (cached prefix + new tokens). The per-layer
# backup hook fires after each layer's full processing, by which point
# layer L's HiCache-loaded prefix KV and forward-written new KV are both
# final — so transferring all of layer L's pages then is correct, and it
# overlaps the (dominant, at high cache-hit) prefix transfer with the
# forward. Verified by output-equality.
end_idx = min(len(req.fill_ids), len(req.origin_input_ids))
page_indices = _kv_locs_to_page_indices_cpu(
self.req_to_token_pool.req_to_token[req.req_pool_idx, 0:end_idx],