Phase 2 of the D→P sync feature (Phase 1 in dc4867c verified the
underlying RDMA link in isolation). This commit wires that link into
each SGLang worker's scheduler so D and P can exchange session KV
without going through the PD prefill pipeline.
New module:
third_party/sglang/python/sglang/srt/disaggregation/snapshot/
controller.py — SnapshotLinkController owns one mooncake transfer
engine per worker, pre-registers all kv_pool layer
buffers, and exposes prepare_receive() and
push_session_kv() APIs. Receive bookkeeping via
a session_id → SnapshotIngestRecord side-table.
Three RPC types added to io_struct.py and full plumbing wired through:
SnapshotPrepareReceiveReqInput/Output P-side alloc + return layout
SnapshotDumpReqInput/Output D-side read kv_pool + RDMA push
SnapshotFinalizeIngestReqInput/Output P-side radix tree insert
Files touched:
managers/io_struct.py 3 new ReqInput/ReqOutput pairs
managers/tokenizer_communicator_mixin.py 3 communicators, 3 awaitables
managers/scheduler.py init controller + 3 handlers
entrypoints/http_server.py 3 HTTP endpoints under /_snapshot
Activation: set SGLANG_SNAPSHOT_LINK_ENABLE=1 (and
SGLANG_SNAPSHOT_LINK_HOST / _PORT / _IB_DEVICE) per worker. Controller
init is opt-in and defaults off, so production PD pipeline is
untouched.
Subsequent work (Phase 3): agentic-pd-hybrid orchestration in
_invoke_kvcache_seeded_router to call prepare_receive on P, dump on
D-old, finalize_ingest on P, then trigger the existing P→D' transfer
which will now hit P's radix cache (skipping re-prefill).
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