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.

serverAppConfigs-docs/LLM/Dual-R9700-Cooperation.md

@@ -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