vulkan: Allow fallback to sysmem memory when vidmem is full #15649
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For performance tuning it is very bad if the program silently falls back to host memory. We had this issue in the past with the CUDA sysmem fallback setting on Windows, to turn it off was basically always the first optimization step recommended, before tuning layers and that kind of thing. We also had this issue in RADV, where this behaviour is the default and no way to turn it off existed until someone added an environment variable for this purpose in Mesa. |
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OK, I added an env var, default behavior remains the same. |
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Yeah please make this hidden behind an envvar, I don't want to submit anyone else to the pain I felt debugging #13765. Setting a smaller number of layers and running the rest on CPU is always going to be faster than swapping. |
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…#15649) * vulkan: Allow fallback to sysmem memory when vidmem is full * vulkan: Add env var GGML_VK_ALLOW_SYSMEM_FALLBACK
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This lets me run gpt-oss-120b-mxfp4 locally, which is useful for testing even though it's obviously going to be slow. I initially thought about putting this behind an env var, but I'm not sure if the current behavior of failing when vidmem is full is really more useful for the average user. I could go either way.