Known issues & hardware limits

Known limitations and their workarounds, mostly GPU/backend specific.

AMD + Vulkan: large image models (Flux, SDXL hi-res) fail to allocate. Symptom: image gen returns 500 - generate_image returned no results; sd-server log shows ggml_vulkan: Requested buffer size exceeds device buffer size limit: ErrorOutOfDeviceMemory and flux: failed to allocate the compute buffer. Cause: AMD's Windows Vulkan driver caps a single memory allocation at 2 GiB (maxMemoryAllocationSize/maxBufferSize), regardless of how much VRAM is free. Flux/SDXL need one contiguous compute buffer larger than that at higher resolutions, so it is rejected even with 20+ GB free. --diffusion-fa (flash attention) is already on and cannot bring it under 2 GiB at high res.

• Workaround: lower the generation resolution (768x768 usually works, 512 is safe). Smaller/distilled diffusion models stay under the cap - e.g. Z-Image-Turbo works fine on Vulkan.
• Real fix for hi-res Flux/SDXL on AMD: use a ROCm/HIP sd-server build (HIP has no 2 GiB single-allocation cap). Set it in Settings -> Backends. Text (llama-server) is unaffected because model weights are split across many sub-2 GiB buffers; only large single diffusion tensors hit the wall.

ggml_cuda_init: failed to initialize CUDA: (null) on every model load. This means the backend binary you are running is a CUDA-compiled build, but no NVIDIA GPU is present (e.g. on an AMD box). At startup llama.cpp/sd.cpp probe for a CUDA device, fail, log this line, then fall back to CPU (slow). It is harmless as a message but means that process is NOT on the GPU. Fix: point Settings -> Backends at a Vulkan (or ROCm) build. A binary compiled without CUDA never prints this line.

AMD GPUs report VRAM only - no temperature / fan / power. On non-NVIDIA Windows GPUs, Quartermaster reads VRAM (total/used) and utilization via DXGI + PDH, but the driver does not expose temp/fan/power the way nvidia-smi does, so those gauges stay blank. Expected, not a bug.

Choosing Vulkan vs ROCm/HIP on AMD. For text (llama-server), Vulkan is the easy, working default. For image generation, prefer ROCm/HIP where you need higher resolution, because of the Vulkan 2 GiB single-allocation cap above.

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