Profiling showed the 2-slot rotation stalls ~5.5ms per layer waiting for
the down_exps upload: 3 tensors per MoE layer need 3 slots for a full
layer of lookahead. Default is now 3 (one layer), configurable via the
env var value, degrading to however many slots fit on OOM.
Also fixes a use-after-free: on a failed slot regrow the repointed
staging tensors kept dangling pointers into freed device memory, which
graph reuse carried into later evals. Staging repoints are now restored
right after kernel launch, slots are sized once from the graph max, and
allocation happens before freeing.
Qwen3.6-35B-A3B pp2048 on RTX 3060: 1643 -> 1880 t/s (mainline: 1143).
At large batch sizes virtually every expert is used, so the per-layer
routing-ids readback that mainline waits on buys nothing while forcing a
full device sync per expert tensor (3x per MoE layer). Above a batch
threshold, upload the full expert tensors through a second backend
instance on the same device (own stream) with two event-ordered staging
slots, so uploads for tensor N+1 overlap compute of tensor N.
Qwen3.6-35B-A3B pp2048 on RTX 3060 (-ncmoe 26, ub 2048): 1383 -> 1663 t/s.
Generation output verified token-identical; decode path unaffected.
Opt-in via GGML_SCHED_PREFETCH_EXPERTS=1.
Wire the existing GGML_CUDA_REGISTER_HOST path back up: after model load,
cudaHostRegister the mmap pages backing weights kept in system memory.
Recovers pageable-copy losses when MoE experts are streamed to the GPU
during prefill (n-cpu-moe): Qwen3.6-35B-A3B pp2048 1144 -> 1385 t/s on
RTX 3060. Opt-in via GGML_CUDA_REGISTER_HOST=1, unchanged otherwise.
Anirban Kar