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- Use 4-D KV cache format (matching SM100) instead of 5-D to avoid stride inheritance bugs in reshape_and_cache_flash - Set prefill wrapper backend to 'auto' on SM120 (no trtllm-gen cubins) - Use BF16 o_dtype for both prefill and decode (FA2 doesn't support FP8 output) - Skip FP8 output buffer for FA2 NVFP4 paths (write BF16 directly) - Add use_fa2_nvfp4_kv attribute to FlashInferImpl for forward path - Remove SM120 5-D special cases in get_kv_cache_shape and get_kv_cache_stride_order Fixes: decode output corruption, MoE illegal memory access, FULL cudagraph compatibility
NVFP4 KV cache does not use scalar q_scale factors (it uses block-level scaling). The checkpoint doesn't provide q_scale for NVFP4, which triggers misleading warnings: 1. "Checkpoint does not provide a q scaling factor" — not applicable to nvfp4 2. "Using KV cache scaling factor 1.0 for fp8_e4m3" — not applicable to nvfp4 Add `kv_cache_dtype != "nvfp4"` guards to both warning conditions.
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Superseded by updated #49891. Scale warning suppression removed after further review — NVFP4 path does not use q_scale, so the warning side-effect is harmless. |
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Summary
When using NVFP4 KV cache (
--kv-cache-dtype nvfp4), the checkpoint doesn't provide scalarq_scalefactors because NVFP4 uses block-level scaling (groups of 16 consecutive head-dim elements). This triggers two misleading warnings on startup:"Checkpoint does not provide a q scaling factor. Setting it to k_scale."— not applicable to NVFP4"Using KV cache scaling factor 1.0 for fp8_e4m3."— not applicable to NVFP4Context
This is part of the SM120 (RTX 5090) NVFP4 KV cache enablement. NVFP4 KV cache stores packed fp4 data + fp8 block scales, which is fundamentally different from FP8 KV cache that uses scalar per-tensor scaling. The
BaseKVCacheMethodinkv_cache.pywas written assuming FP8-style scalar scaling and doesn't account for NVFP4's block-level approach.The NVFP4 KV cache layout on SM120 uses:
(B, 2*N_kv, N, F)for compatibility withreshape_and_cache_flashFix
Add
kv_cache_dtype != "nvfp4"guards to both warning conditions inBaseKVCacheMethod.Files Changed
vllm/model_executor/layers/quantization/kv_cache.pyRelated
Part of SM120 NVFP4 KV cache enablement:
Test Plan
--kv-cache-dtype nvfp4and verify no spurious scale warnings--kv-cache-dtype fp8and verify warnings still appear when appropriate