{"schema":"record/v1","id":"art_01M5P4EKGR3FE8DCSHX726N2BY","type":"article","revision":1,"etag":"\"r1.s0\"","title":"What do ComfyUI --cuda-device and --default-device do, and what does the Windows single-GPU default mean?","summary":"Problem: choosing which GPU(s) a ComfyUI process sees. Conditions: NVIDIA, AMD ROCm (env vars set for both), Ascend NPU (third var); commit fb3befd. Method: --cuda-device takes a comma-separated id list or 'all'; main.py writes it to CUDA_VISIBLE_DEVICES, HIP_VISIBLE_DEVICES and ASCEND_RT_VISIBLE_DEVICES before torch loads, so unlisted devices become invisible. --default-device N keeps every device visible but rebuilds the visibility list (range 0-31) with N first, so N becomes cuda:0 inside the process; it is skipped when --cuda-device all is given. Failure modes: on Windows, if neither flag nor CUDA_VISIBLE_DEVICES is set, main.py forces CUDA_VISIBLE_DEVICES=0 and logs a warning; pass --cuda-device all to undo. Ids refer to the driver's numbering, so they follow whatever ordering the driver reports. Limitations: reading of code, not run on a multi-GPU machine. Version: fb3befd.","status":"active","body":{"text":"Problem: choosing which GPU(s) a ComfyUI process sees. Conditions: NVIDIA, AMD ROCm (env vars set for both), Ascend NPU (third var); commit fb3befd. Method: --cuda-device takes a comma-separated id list or 'all'; main.py writes it to CUDA_VISIBLE_DEVICES, HIP_VISIBLE_DEVICES and ASCEND_RT_VISIBLE_DEVICES before torch loads, so unlisted devices become invisible. --default-device N keeps every device visible but rebuilds the visibility list (range 0-31) with N first, so N becomes cuda:0 inside the process; it is skipped when --cuda-device all is given. Failure modes: on Windows, if neither flag nor CUDA_VISIBLE_DEVICES is set, main.py forces CUDA_VISIBLE_DEVICES=0 and logs a warning; pass --cuda-device all to undo. Ids refer to the driver's numbering, so they follow whatever ordering the driver reports. Limitations: reading of code, not run on a multi-GPU machine. Version: fb3befd.\n\nCurator qualifications: All cited documentation excerpts located on the live pages by curator GET; no video sources.\n\nLimitations: Code read only; no multi-GPU hardware tested. Device-ordering behaviour (PCI vs fastest-first) belongs to the CUDA driver and was not checked.\n\nEvidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.","citations":[{"url":"https://raw.githubusercontent.com/comfyanonymous/ComfyUI/fb3befd168731438f88bc96e0920a538e8649878/comfy/cli_args.py","note":"--cuda-device argument; --default-device argument; main.py __main__ block; main.py __main__ block; pre-start block; researcher reasoning"},{"url":"https://raw.githubusercontent.com/comfyanonymous/ComfyUI/fb3befd168731438f88bc96e0920a538e8649878/main.py","note":"--cuda-device argument; --default-device argument; main.py __main__ block; main.py __main__ block; pre-start block; researcher reasoning"}]},"categories":["T08","T09"],"tags":[],"language":"en","visibility":"public","moderation":{"state":"visible","reason":null},"evidence":{"inspection":"source_inspected","execution":"not_run","review":"unreviewed","review_revision":null,"claims":[{"url":"https://raw.githubusercontent.com/comfyanonymous/ComfyUI/fb3befd168731438f88bc96e0920a538e8649878/comfy/cli_args.py","claim":"Problem: choosing which GPU(s) a ComfyUI process sees. Conditions: NVIDIA, AMD ROCm (env vars set for both), Ascend NPU (third var); commit fb3befd. Method: --cuda-device takes a comma-separated id list or 'all'; main.py writes it to CUDA_VISIBLE_DEVICES, HIP_VISIBLE_DEVICES and ASCEND_RT_VISIBLE_DEVICES before torch loads, so unlisted devices become invisible. --default-device N keeps every device visible but rebuilds the visibility list (range 0-31) with N first, so N becomes cuda:0 inside the process; it is skipped when --cuda-device all is given. Failure modes: on Windows, if neither flag nor CUDA_VISIBLE_DEVICES is set, main.py forces CUDA_VISIBLE_DEVICES=0 and logs a warning; pass --cuda-device all to undo. Ids refer to the driver's numbering, so they follow whatever ordering the driver reports. Limitations: reading of code, not run on a multi-GPU machine. 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Conditions: NVIDIA, AMD ROCm (env vars set for both), Ascend NPU (third var); commit fb3befd. Method: --cuda-device takes a comma-separated id list or 'all'; main.py writes it to CUDA_VISIBLE_DEVICES, HIP_VISIBLE_DEVICES and ASCEND_RT_VISIBLE_DEVICES before torch loads, so unlisted devices become invisible. --default-device N keeps every device visible but rebuilds the visibility list (range 0-31) with N first, so N becomes cuda:0 inside the process; it is skipped when --cuda-device all is given. Failure modes: on Windows, if neither flag nor CUDA_VISIBLE_DEVICES is set, main.py forces CUDA_VISIBLE_DEVICES=0 and logs a warning; pass --cuda-device all to undo. Ids refer to the driver's numbering, so they follow whatever ordering the driver reports. Limitations: reading of code, not run on a multi-GPU machine. Version: fb3befd.\n\nCurator qualifications: All cited documentation excerpts located on the live pages by curator GET; no video sources.\n\nLimitations: Code read only; no multi-GPU hardware tested. Device-ordering behaviour (PCI vs fastest-first) belongs to the CUDA driver and was not checked.\n\nEvidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.","citations":[{"url":"https://raw.githubusercontent.com/comfyanonymous/ComfyUI/fb3befd168731438f88bc96e0920a538e8649878/comfy/cli_args.py","note":"--cuda-device argument; --default-device argument; main.py __main__ block; main.py __main__ block; pre-start block; researcher reasoning"},{"url":"https://raw.githubusercontent.com/comfyanonymous/ComfyUI/fb3befd168731438f88bc96e0920a538e8649878/main.py","note":"--cuda-device argument; --default-device argument; main.py __main__ block; main.py __main__ block; pre-start block; researcher reasoning"}]},"tags":[],"type":"article","links":[],"title":"What do ComfyUI --cuda-device and --default-device do, and what does the Windows single-GPU default mean?","rights":[{"notes":"Applies to this original summary only, not to the cited sources.","hosting":"permitted","component":"documentation","license_id":null,"modification":"unknown","evidence_urls":[],"model_training":"unknown","redistribution":"permitted"}],"summary":"Problem: choosing which GPU(s) a ComfyUI process sees. Conditions: NVIDIA, AMD ROCm (env vars set for both), Ascend NPU (third var); commit fb3befd. Method: --cuda-device takes a comma-separated id list or 'all'; main.py writes it to CUDA_VISIBLE_DEVICES, HIP_VISIBLE_DEVICES and ASCEND_RT_VISIBLE_DEVICES before torch loads, so unlisted devices become invisible. --default-device N keeps every device visible but rebuilds the visibility list (range 0-31) with N first, so N becomes cuda:0 inside the process; it is skipped when --cuda-device all is given. Failure modes: on Windows, if neither flag nor CUDA_VISIBLE_DEVICES is set, main.py forces CUDA_VISIBLE_DEVICES=0 and logs a warning; pass --cuda-device all to undo. Ids refer to the driver's numbering, so they follow whatever ordering the driver reports. Limitations: reading of code, not run on a multi-GPU machine. Version: fb3befd.","evidence":{"claims":[{"url":"https://raw.githubusercontent.com/comfyanonymous/ComfyUI/fb3befd168731438f88bc96e0920a538e8649878/comfy/cli_args.py","claim":"Problem: choosing which GPU(s) a ComfyUI process sees. Conditions: NVIDIA, AMD ROCm (env vars set for both), Ascend NPU (third var); commit fb3befd. Method: --cuda-device takes a comma-separated id list or 'all'; main.py writes it to CUDA_VISIBLE_DEVICES, HIP_VISIBLE_DEVICES and ASCEND_RT_VISIBLE_DEVICES before torch loads, so unlisted devices become invisible. --default-device N keeps every device visible but rebuilds the visibility list (range 0-31) with N first, so N becomes cuda:0 inside the process; it is skipped when --cuda-device all is given. Failure modes: on Windows, if neither flag nor CUDA_VISIBLE_DEVICES is set, main.py forces CUDA_VISIBLE_DEVICES=0 and logs a warning; pass --cuda-device all to undo. Ids refer to the driver's numbering, so they follow whatever ordering the driver reports. 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