docs: the LLM index and the cooperation page catch up with layer split
The LLM index still opened with vllm-radiance as frank-medium's runtime and drew the replica pair in its topology diagram; the cooperation page's thesis (collectives are impossible, so the answer is hardware) now has to name the path the fleet actually took: llama.cpp's layer split, which launches no RCCL kernel on either card. That reframes the M.2 riser as a means to TENSOR parallelism rather than a means to using both cards at all.
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@@ -123,11 +123,11 @@ sudo lspci -vv -s <card2> | grep AtomicOpsCtl # want: ReqEn+
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```
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If that reads `ReqEn+`, the rest is mechanical: `--tensor-parallel-size 2` with
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`HIP_VISIBLE_DEVICES=0,1`, then the same benchmark set used for the replicas
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(`scripts/bench-vllm-corpus.py` / `bench-turn-latency.py`) so the two
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architectures are compared on identical workloads. If it still reads `ReqEn-`,
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the card is still on a non-atomic path — check `lspci -tv` for the bridge chain
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rather than assuming the move worked.
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`HIP_VISIBLE_DEVICES=0,1`, then the same benchmark set
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(`scripts/bench-turn-latency.py`, and the endpoint's own `timings` block) so the
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two architectures are compared on identical workloads. If it still reads
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`ReqEn-`, the card is still on a non-atomic path — check `lspci -tv` for the
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bridge chain rather than assuming the move worked.
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**Rule for any future multi-GPU collective experiment: stop and mask the
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production service first** (`sudo systemctl stop frank-medium && sudo systemctl
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@@ -138,6 +138,29 @@ power cycle). The mechanism is not proven, but a hung AQL dispatch wedging the
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GPU driver is a plausible cause and this host has precedent for going
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unreachable until a power cycle.
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## The third path, and the one in production: llama.cpp's layer split
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Everything above is about *collectives*, and vLLM cannot proceed without them
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in any of its parallelisms — TP needs a per-layer allreduce, and PP's stage
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handoff is a p2p `send`/`recv` of the hidden state, the primitive this host
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also fails. **llama.cpp's `--split-mode layer` needs no collective at all**:
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layers are distributed across the cards and the boundary activation is a
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plain per-backend copy, once per forward pass. No RCCL kernel is ever launched
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on the second card, so the atomics gate never comes up.
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That is what `frank-medium` runs today ([[frank-medium-llamacpp-dflash2]]): one
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process, one model, both cards, 262144 context. Measured against tensor split
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on this host: 1991 t/s prefill / 18.8 tok/s decode layer-split, against 272 /
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26.3 tensor (butterfly fallback, no RCCL). Tensor would still win decode on a
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build with a working RCCL — which is exactly what the M.2 riser or a board swap
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in [the short answer](#the-short-answer) would buy.
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So the ranking changed on 2026-09-16: software already gets both cards onto one
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model, and the hardware fix is no longer a means to that end — it is a means to
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*tensor* parallelism, which buys ~40 % decode and would let this runtime drop
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layer-split's serial stages entirely.
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## What would change the answer
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- An RCCL build whose kernels stop declaring a hostcall buffer — the one
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@@ -1,11 +1,13 @@
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# LLM Fleet — Knowledge Base
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Documentation for the LLM inference fleet on the two hosts (2026-09-16):
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vllm-radiance on Dankserver (frank-medium, just1moremodel
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Qwen3.8-27B-Uncensored-MXFP4-awq on 2x Radeon AI PRO R9700) and TWO endpoints on
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Dankclaw — halogen-flash-server (frank-large, Qwen3.8-Flash-Next w4b on the
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gfx1151 iGPU, port 7770) and mainline llama.cpp (frank-small, ISTA-DASLab
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Qwen3.8-27B-GSQ-RCO IQ3_S with MTP and vision on the RTX 3090, port 7771).
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**mainline llama.cpp on Dankserver** serving frank-medium as one layer-split
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process across both Radeon AI PRO R9700 cards (ajgazin Swift-Qwen3.8-27B-
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Uncensored-Dynamic-MTP UD-Q8_K_XL + the z-lab DFlash2 drafter), and TWO
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endpoints on Dankclaw — halogen-flash-server (frank-large, Qwen3.8-Flash-Next
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w4b on the gfx1151 iGPU, port 7770) and mainline llama.cpp (frank-small,
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ISTA-DASLab Qwen3.8-27B-GSQ-RCO IQ3_S with MTP and vision on the RTX 3090, port
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7771).
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> 2026-08-22: the former `vllmScripts` repository is merged into the
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> serverAppConfigs repository. This knowledge base moved from the old repo's
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@@ -19,10 +21,10 @@ graph LR
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subgraph Dankserver[AMD Dankserver - Ubuntu 26.04]
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A[2x Radeon AI PRO R9700
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gfx1201, 32 GiB each]
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B2[vllm-radiance MXFP4
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B2[llama.cpp, layer split
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frank-medium, port 7770]
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C[Qwen3.8-27B-Uncensored-MXFP4-awq
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2 single-GPU replicas, 114688 ctx / 4 seqs, DFlash2]
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C[Swift-Qwen3.8-27B-Uncensored UD-Q8_K_XL
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ONE process on both cards, 262144 ctx / 1 slot, DFlash2]
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A --> B2 --> C
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end
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@@ -54,13 +56,18 @@ frank-small, port 7771]
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## Active Deployment
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- [[frank-medium-radiance-mxfp4]] — the ACTIVE frank-medium runbook: the
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vllm-radiance MXFP4 stack (stilldeadcode/vllm-radiance:0.9.3 +
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- [[frank-medium-llamacpp-dflash2]] — the ACTIVE frank-medium runbook since
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2026-09-16: mainline llama.cpp serving
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ajgazin/Swift-Qwen3.8-27B-Uncensored-Dynamic-MTP-GGUF at UD-Q8_K_XL with the
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z-lab DFlash2 Q8_0 drafter on Dankserver's 2x Radeon AI PRO R9700, as ONE
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layer-split process behind :7770 (tensor parallelism is impossible on this
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host — the second card cannot dispatch an RCCL collective)
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- [[frank-medium-radiance-mxfp4]] — RETIRED 2026-09-16, one day after it was
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deployed: the vllm-radiance MXFP4 stack (stilldeadcode/vllm-radiance:0.9.3 +
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ggz14/radiance-vllm-mxfp4 patches) serving
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just1moremodel/Qwen3.8-27B-Uncensored-MXFP4-awq on Dankserver's 2x Radeon
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AI PRO R9700 as two single-GPU replicas behind a round-robin proxy, with
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the PCIe-atomics evidence that rules out TP=2 on this host (since
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2026-09-15/16)
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just1moremodel/Qwen3.8-27B-Uncensored-MXFP4-awq as two single-GPU replicas
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behind a round-robin proxy; kept as the record of the deployment it
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succeeded, plus the PCIe-atomics evidence that rules out TP=2 on this host
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- [[frank-medium-rocmfpx]] — PRIOR frank-medium deployment (llama.cpp era,
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2026-09-15): charlie12345/ROCmFPX serving
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kingjones777/Qwen3.8-27B-ROCmFPX-Q8_0-AGENT-GGUF; kept as the record of the
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