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.
This commit is contained in:
Frank
2026-09-16 15:39:47 -07:00
parent 87492c7b10
commit c97e359bc2
2 changed files with 49 additions and 19 deletions
@@ -123,11 +123,11 @@ sudo lspci -vv -s <card2> | grep AtomicOpsCtl # want: ReqEn+
```
If that reads `ReqEn+`, the rest is mechanical: `--tensor-parallel-size 2` with
`HIP_VISIBLE_DEVICES=0,1`, then the same benchmark set used for the replicas
(`scripts/bench-vllm-corpus.py` / `bench-turn-latency.py`) so the two
architectures are compared on identical workloads. If it still reads `ReqEn-`,
the card is still on a non-atomic path — check `lspci -tv` for the bridge chain
rather than assuming the move worked.
`HIP_VISIBLE_DEVICES=0,1`, then the same benchmark set
(`scripts/bench-turn-latency.py`, and the endpoint's own `timings` block) so the
two architectures are compared on identical workloads. If it still reads
`ReqEn-`, the card is still on a non-atomic path — check `lspci -tv` for the
bridge chain rather than assuming the move worked.
**Rule for any future multi-GPU collective experiment: stop and mask the
production service first** (`sudo systemctl stop frank-medium && sudo systemctl
@@ -138,6 +138,29 @@ power cycle). The mechanism is not proven, but a hung AQL dispatch wedging the
GPU driver is a plausible cause and this host has precedent for going
unreachable until a power cycle.
## The third path, and the one in production: llama.cpp's layer split
Everything above is about *collectives*, and vLLM cannot proceed without them
in any of its parallelisms — TP needs a per-layer allreduce, and PP's stage
handoff is a p2p `send`/`recv` of the hidden state, the primitive this host
also fails. **llama.cpp's `--split-mode layer` needs no collective at all**:
layers are distributed across the cards and the boundary activation is a
plain per-backend copy, once per forward pass. No RCCL kernel is ever launched
on the second card, so the atomics gate never comes up.
That is what `frank-medium` runs today ([[frank-medium-llamacpp-dflash2]]): one
process, one model, both cards, 262144 context. Measured against tensor split
on this host: 1991 t/s prefill / 18.8 tok/s decode layer-split, against 272 /
26.3 tensor (butterfly fallback, no RCCL). Tensor would still win decode on a
build with a working RCCL — which is exactly what the M.2 riser or a board swap
in [the short answer](#the-short-answer) would buy.
So the ranking changed on 2026-09-16: software already gets both cards onto one
model, and the hardware fix is no longer a means to that end — it is a means to
*tensor* parallelism, which buys ~40 % decode and would let this runtime drop
layer-split's serial stages entirely.
## What would change the answer
- An RCCL build whose kernels stop declaring a hostcall buffer — the one
+21 -14
View File
@@ -1,11 +1,13 @@
# LLM Fleet — Knowledge Base
Documentation for the LLM inference fleet on the two hosts (2026-09-16):
vllm-radiance on Dankserver (frank-medium, just1moremodel
Qwen3.8-27B-Uncensored-MXFP4-awq on 2x Radeon AI PRO R9700) and TWO endpoints on
Dankclaw — halogen-flash-server (frank-large, Qwen3.8-Flash-Next w4b on the
gfx1151 iGPU, port 7770) and mainline llama.cpp (frank-small, ISTA-DASLab
Qwen3.8-27B-GSQ-RCO IQ3_S with MTP and vision on the RTX 3090, port 7771).
**mainline llama.cpp on Dankserver** serving frank-medium as one layer-split
process across both Radeon AI PRO R9700 cards (ajgazin Swift-Qwen3.8-27B-
Uncensored-Dynamic-MTP UD-Q8_K_XL + the z-lab DFlash2 drafter), and TWO
endpoints on Dankclaw — halogen-flash-server (frank-large, Qwen3.8-Flash-Next
w4b on the gfx1151 iGPU, port 7770) and mainline llama.cpp (frank-small,
ISTA-DASLab Qwen3.8-27B-GSQ-RCO IQ3_S with MTP and vision on the RTX 3090, port
7771).
> 2026-08-22: the former `vllmScripts` repository is merged into the
> serverAppConfigs repository. This knowledge base moved from the old repo's
@@ -19,10 +21,10 @@ graph LR
subgraph Dankserver[AMD Dankserver - Ubuntu 26.04]
A[2x Radeon AI PRO R9700
gfx1201, 32 GiB each]
B2[vllm-radiance MXFP4
B2[llama.cpp, layer split
frank-medium, port 7770]
C[Qwen3.8-27B-Uncensored-MXFP4-awq
2 single-GPU replicas, 114688 ctx / 4 seqs, DFlash2]
C[Swift-Qwen3.8-27B-Uncensored UD-Q8_K_XL
ONE process on both cards, 262144 ctx / 1 slot, DFlash2]
A --> B2 --> C
end
@@ -54,13 +56,18 @@ frank-small, port 7771]
## Active Deployment
- [[frank-medium-radiance-mxfp4]] — the ACTIVE frank-medium runbook: the
vllm-radiance MXFP4 stack (stilldeadcode/vllm-radiance:0.9.3 +
- [[frank-medium-llamacpp-dflash2]] — the ACTIVE frank-medium runbook since
2026-09-16: mainline llama.cpp serving
ajgazin/Swift-Qwen3.8-27B-Uncensored-Dynamic-MTP-GGUF at UD-Q8_K_XL with the
z-lab DFlash2 Q8_0 drafter on Dankserver's 2x Radeon AI PRO R9700, as ONE
layer-split process behind :7770 (tensor parallelism is impossible on this
host — the second card cannot dispatch an RCCL collective)
- [[frank-medium-radiance-mxfp4]] — RETIRED 2026-09-16, one day after it was
deployed: the vllm-radiance MXFP4 stack (stilldeadcode/vllm-radiance:0.9.3 +
ggz14/radiance-vllm-mxfp4 patches) serving
just1moremodel/Qwen3.8-27B-Uncensored-MXFP4-awq on Dankserver's 2x Radeon
AI PRO R9700 as two single-GPU replicas behind a round-robin proxy, with
the PCIe-atomics evidence that rules out TP=2 on this host (since
2026-09-15/16)
just1moremodel/Qwen3.8-27B-Uncensored-MXFP4-awq as two single-GPU replicas
behind a round-robin proxy; kept as the record of the deployment it
succeeded, plus the PCIe-atomics evidence that rules out TP=2 on this host
- [[frank-medium-rocmfpx]] — PRIOR frank-medium deployment (llama.cpp era,
2026-09-15): charlie12345/ROCmFPX serving
kingjones777/Qwen3.8-27B-ROCmFPX-Q8_0-AGENT-GGUF; kept as the record of the