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[P/D] Add cpu device support for nixl_connector #27510

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[P/D] Add cpu device support for nixl_connector #27510

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add cpu device support for nixl
ZhengHongming888 Oct 25, 2025
448b0da
Merge branch 'vllm-project:main' into add_cpu_device_for_nixl
ZhengHongming888 Nov 3, 2025
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1 change: 1 addition & 0 deletions vllm/distributed/kv_transfer/kv_connector/v1/nixl_connector.py
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Expand Up @@ -89,6 +89,7 @@
),
"tpu": ("cpu",),
"xpu": ("cpu",),
"cpu": ("cpu",),
}
Comment on lines 89 to 93
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@chatgpt-codex-connector chatgpt-codex-connector bot Oct 28, 2025

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P1 Badge Enabling CPU device hits unimplemented buffer copy APIs

Adding "cpu": ("cpu",) makes the Nixl connector accept CPU hosts, but the CPU platform still lacks the copy primitives that copy_kv_blocks() uses when kv_buffer_device == "cpu". After a transfer completes, get_finished() calls sync_recved_kv_to_device/save_kv_to_host, which invoke copy_kv_blocks. That function delegates to current_platform.insert_blocks_to_device or swap_out_blocks_to_host (see kv_connector/utils.py), neither of which exist on CpuPlatform. As soon as a request is received or saved, this path will raise an AttributeError, so a CPU-only deployment cannot actually run. Either avoid host-buffer copies for CPU or implement the required methods in CpuPlatform before advertising CPU support here.

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@njhill njhill Oct 28, 2025

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@ZhengHongming888 this is a good point. Will this change actually have any use without other changes?

# support for oot platform by providing mapping in current_platform
_NIXL_SUPPORTED_DEVICE.update(current_platform.get_nixl_supported_devices())
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