prain: README; example config with the measured eGPU defaults (miss auto <=2 tokens, 16 CPU threads, no pinned RAM tier)

examples/gemma4-26b-a4b-rx6600xt.toml

@@ -1,6 +1,9 @@
 # prain placement: prithivMLmods/gemma-4-26B-A4B-it-Uncensored-MAX on an 8 GB RX 6600 XT
 # Model: 30 MoE layers x 128 experts, top-8 routing, 11.34 MiB per expert (BF16).
-# VRAM: 8 GiB - 4.45 GiB dense weights - 0.75 GiB KV cache - ~0.9 GiB runtime = ~1.7 GiB experts.
+# VRAM, measured: 6.22 GiB weights (4.46 dense + 5 slots x 30 layers) + 0.75 GiB KV cache: 7.9 of
+# 8 GiB in use. Serve with --attention-backend TRITON_ATTN (ROCM_ATTN needs more LDS than RDNA2 has).
+# RAM tier: pinning is very slow behind a strict IOMMU (Thunderbolt eGPU: minutes per GiB), so this
+# file keeps no RAM tier; the kernel page cache holds the hot part of the pack instead.
 #
 # Tiers:  vram = pinned in a VRAM slot for the whole run
 #         ram  = pinned host memory, copied into a cache slot when a token needs it
@@ -38,10 +41,11 @@ budget = 2            # experts per layer and forward
 min_prob = 0.05       # skip guesses below this router probability
 
 [miss]                # an expert that is not in VRAM
-mode = "copy"         # copy | cpu (always compute it on the CPU) | auto (CPU if it has
-cpu_max_tokens = 1    #   at most cpu_max_tokens tokens, else copy)
-cpu_threads = 4       # CPU threads of the vLLM worker (sets OMP_NUM_THREADS)
-admit = 1             # cpu/auto: copy this many CPU-run experts into VRAM afterwards
+mode = "auto"         # copy | cpu (always compute it on the CPU) | auto (CPU if it has
+cpu_max_tokens = 2    #   at most cpu_max_tokens tokens, else copy). Measured on the Thunderbolt
+                      #   eGPU host: a copy costs ~4.6 ms + disk read, the CPU ~2.5 ms per token
+cpu_threads = 16      # CPU threads of the vLLM worker (sets OMP_NUM_THREADS)
+admit = 0             # cpu/auto: copy this many CPU-run RAM-tier experts into VRAM afterwards
 
 [serve]               # parallel requests (`prain serve` passes these to vLLM)
 max_requests = 2      # requests vLLM runs at once (--max-num-seqs); warm-ups count too