# DCP2 extraction from Aiden's production-1.1 image (2026-09-12)

Everything needed to port Aiden's DCP2 (decode context parallelism) stack onto our
clone-at-pin DSV4.1 tree — extracted from `aidendle94/sparkrun-vllm-dsv41-gb10:
production-1.1` (published 2026-09-11T16:54Z; the DCP2 A/B ran on it, report in
`recipes/dsv41-flash-4x-aiden11/reports/2026-09-12_003640_aiden11-dcp2-0912.md`).

## A/B verdict first (why this is optional, not urgent)

Aiden 1.1 DCP2 (300K ctx, dcp=2, a2a, 8 GiB KV) vs our b12x baseline (512K ctx):

| | our b12x (live) | Aiden 1.1 DCP2 |
|---|---|---|
| score | **167/176** | 158/176 |
| pp/tg/TTFT (d0 c1, ms) | **1,642 / 47.0 / 1,738** | 1,517 / 41.8 / 2,446 |
| KV | ~2M tokens @512K | **2,518,386 @300K** |

DCP2 buys KV capacity / high-concurrency headroom, not quality or single-stream
speed. Port it only if we want the 2.5M-token KV on our (fresher) stack.

## What the image contains

- Base: `vllm/vllm-openai:nightly-8a728663` — an **older** vLLM tree (before
  DSV4.1 landed in-tree; it has no `models/deepseek_v4_1/` at all). Aiden's
  overlay adds the model files + the DCP2 machinery; the 24-file manifest is
  `/opt/dsv41-dcp2-mounts.txt` (copied to `manifest.txt` here).
- FlashInfer: **zero porting work** — our FI pin `07869c61` already ships
  `csrc/trtllm_dcp_alltoall.cu`, `flashinfer/cake_dcp.py`, and the bench.
- DCP CLI: `--decode-context-parallel-size N` (`-dcp`), `--dcp-comm-backend
  {ag_rs|a2a}` (default ag_rs; the a2a path is the new all-to-all with LSE
  exchange). Env (image defaults in brackets, all OFF): `DSV41_DCP_STAGE [3]`,
  `DSV41_DCP_COMBINE [ag_rs]`, `DSV41_DCP_PREFILL_GATHER [0]`,
  `DSV41_ENGRAM_MMAP [0]`, `DSV41_ENGRAM_PREFETCH [0]` (+MODE/THREADS/... ).

## Contents

| path | what |
|---|---|
| `manifest.txt` | 23 (flat name, vllm-relative target) pairs from the image |
| `baked/` | the 23 final (patched) files, `docker cp`'d from site-packages |
| `base-theirs/` | the same 16 files at their base commit `8a728663` (GitHub) |
| `base-ours/` | the same 23 files at our pin `e47aa780` (GitHub) |
| `aiden-dcp2.patch` | their 16-file delta (base-theirs → baked), headers rewritten to `a/vllm/… b/vllm/…` for apply at the vLLM source root |

## Porting assessment (dry-run against our pin, 2026-09-12)

| bucket | files | notes |
|---|---|---|
| clean `git apply` | 12 | communication_op, fused_moe/b12x, weight_utils, v1/attention/backend, mla/compressor_utils, kv_cache_coordinator, kv_cache_interface, cp_utils, gpu/attn_utils, gpu/block_table, gpu/model_runner, dflash/speculator — their base == our tree byte-for-byte |
| needs 3-way merge | 4 | `sparse_attn_indexer.py`, `mla/indexer.py`, `mla/sparse_swa.py`, `kv_cache_utils.py` — our pin is newer in these (their base 8a728663 predates our e47aa780 for these paths) |
| new-in-their-tree | 7 | `models/deepseek_v4_1/*` (6) + `candidate_blocks.py` — their base has no `deepseek_v4_1` at all; the overlay adds it. Our tree has newer versions in-tree; only the DCP2-specific deltas are wanted (largest: `engram.py` 773 diff lines, `nvidia/flashinfer_sparse.py` 681, `candidate_blocks.py` 254 — cherry-pick from `baked/` vs `base-ours/`, don't adopt wholesale) |

Total estimate: a few hours of focused work (12 mechanical + 4 small merges +
7 cherry-picks) + one dgx5 rebuild + an A/B. The 7 model files are the risky
part — their `engram.py` (70 KB) is much larger than ours (38 KB): the DCP2
mmap/prefetch machinery lives there.

## Apply procedure (when the day comes)

```
cd <vllm source checkout @ e47aa780>
git apply --check dcp2/aiden-dcp2.patch        # 12 clean, 4 expected failures
# merge the 4 manually (per-file diffs inside aiden-dcp2.patch)
# cherry-pick the 7 model-file deltas by hand
# build with the usual clone-at-pin driver (DCP2 flags stay OFF unless the
# recipe sets --decode-context-parallel-size 2 --dcp-comm-backend a2a + envs)
```