Model cannot SPLIT TENSOR and will not work in consumer multi gpu

#62
by Dr-Ojinsky - opened

0.00.407.274 I print_info: file size = 157.54 GiB (7.65 BPW)
0.00.415.334 E llama_model_load: error loading model: LLAMA_SPLIT_MODE_TENSOR not implemented for architecture 'qwen4exp'
0.00.415.345 E llama_model_load_from_file_impl: failed to load model
0.00.415.351 E cmn common_init_: failed to load model 'c:\AI_Models\Qwen3.8-Flash-Next-UD-Q6_K_XL-00001-of-00006.gguf'
0.00.415.355 E srv load_model: failed to load model, 'c:\AI_Models\Qwen3.8-Flash-Next-UD-Q6_K_XL-00001-of-00006.gguf'
0.00.415.361 I srv operator(): operator(): cleaning up before exit...
0.00.416.547 E srv llama_server: exiting due to model loading error

Yes, this is happening to my also. I got two rtx 3080 with 20GB VRAM each. If I use "-fit on" and llama uses both gpus, the final speed is worse than if I were using just one GPU. My CPU is a ryzen 3700x with 128GB VRAM 3600mhz

llama version used: b11040
layer split doesn't work.

I have tried an unsloth version Q2_K_XL on my MacBook Pro M5 max (128gb). It uses about 80gb of ram. And it is VERY good (an understatement!). And it quite fast too. Very impressive. I have used this model for my meeting summaries and it is way better than any local model I have tried so far. I have not tried it for coding, but I will.

The error only concerns -sm tensor. The current server README lists it as tensor: split weights and KV across GPUs (parallelized, EXPERIMENTAL), and it hasn't been implemented for qwen4exp. -sm layer is the default and does load. On consumer cards, tensor split wouldn't be the win anyway: most of this model has to sit in system RAM, so the offload split matters much more than how the GPUs share the work.

@Nerdsking some estimates for 2×20 GB + 128 GB DDR4-3600, using unsloth's file sizes, 64K context at f16 KV and ~1.5 GiB of buffers:

  • UD-IQ4_XS (93.7 GB): one GPU needs -ncmoe 39 → ~18 GiB VRAM, ~45 GiB RAM. Two GPUs need only -ncmoe 21 → ~38.5 GiB VRAM, ~25 GiB RAM.
  • UD-Q4_K_XL (111 GB): one GPU -ncmoe 41, two GPUs -ncmoe 27 (~41 GiB RAM).
  • On top of that, the ~26.8 GiB n-gram table stays on the CPU side. It's read lazily from the mmapped file.

Decode is bound by what's read from RAM per token (10 of 512 experts active). Dual-channel DDR4-3600 is ~57.6 GB/s. For IQ4_XS that gives roughly 12–20 tok/s on one card vs 16–27 tok/s on two, so the second card should help, not hurt.

If two GPUs came out slower, I'd check two things:

  1. Is --fit (on by default) actually moving fewer experts to the CPU when both GPUs are visible? If it keeps the same -ncmoe, you pay the pipeline hop and gain nothing.
  2. With -ncmoe N set by hand, layers 0..N-1 are light on the GPU. Under layer split, GPU0 gets mostly light layers unless you adjust -ts.

Setting -ncmoe explicitly plus -ts and comparing llama-bench numbers against one GPU should show which one it is.

For the Q6_K_XL (157.5 GiB): 40 GiB VRAM + 128 GB RAM ≈ 159 GiB total, so it won't realistically fit next to the OS.

I got these per-file numbers from a calculator I built for -ncmoe: https://modelvram.com/moe-offload-calculator/ (I built this). They're bandwidth estimates, not measurements.

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