Function w4a16_gemv_dual_sw 

pub fn w4a16_gemv_dual_sw(
    gpu: &dyn GpuBackend,
    kernel: KernelHandle,
    input: DevicePtr,
    weight1: &QuantizedWeight,
    output1: DevicePtr,
    weight2: &QuantizedWeight,
    output2: DevicePtr,
    n: u32,
    k: u32,
    stream: u64,
) -> Result<()>

Single-warp-per-output variant of w4a16_gemv_dual (8 outputs/block → N/8 grid). Bit-identical output (see w4a16_gemv_fused.cu). Default ON via ModelLevers::gemv_sw; kill with ATLAS_NO_GEMV_SW=1.