a1558b6e5087d11053e18040ed96f43bd44100d0
CCCL tuning_radix_sort.cuh teaches: when one kernel in a chain is unavailable, replace ONLY that kernel while keeping downstream native ops alive. Our MoE chain: topk_softmax → moe_align_block_size → invoke_fused_moe_kernel BI-V100 ixformer lacks vllm_moe_topk_softmax, which killed the ENTIRE chain and forced 100% PyTorch fallback (_pure_pytorch_experts: 256x F.linear loop). Fix: Add try/except in topk_softmax with PyTorch fallback (softmax+topk). Now the chain can proceed to native align+invoke kernels if they exist. Also: dont permanently disable native path after first failure — retry once. CCCL source: catch2_test_device_radix_sort_pairs.cu + tuning_radix_sort.cuh Maps to: _custom_ops.py (topk_softmax) + qwen3_5.py (MoE forward)
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