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[OMNIML-2336] make w4a8_nvfp4_fp8's scale factor in range of 448/6 #406

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Oct 16, 2025
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[OMNIML-2336] make w4a8_nvfp4_fp8's scale factor in range of 448/6 #406

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17 changes: 13 additions & 4 deletions modelopt/torch/export/quant_utils.py
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Original file line number Diff line number Diff line change
Expand Up @@ -270,12 +270,18 @@ def get_weight_scaling_factor(module: nn.Module, weight_name: str = "weight") ->
QUANTIZATION_NVFP4_AWQ,
QUANTIZATION_W4A8_NVFP4_FP8,
]:
if quantization_format == QUANTIZATION_W4A8_NVFP4_FP8:
# weight_scaling_factor_2 for w4a8 needs to be amax/448, so that the wsf is in range 448/6.
# This is because the kernel dequantizes weight to fp8, which is in range 448.
weight_scaling_factor_2 = weight_quantizer._amax.float() / 448.0
else:
weight_scaling_factor_2 = NVFP4QTensor.get_weights_scaling_factor_2_from_quantizer(
weight_quantizer
)
return NVFP4QTensor.get_weights_scaling_factor(
weight,
weight_quantizer.block_sizes[-1],
NVFP4QTensor.get_weights_scaling_factor_2_from_quantizer(weight_quantizer).to(
weight.device
),
weight_scaling_factor_2.to(weight.device),
)[0]

if quantization_format in [QUANTIZATION_W4A8_MXFP4_FP8, QUANTIZATION_MXFP4]:
Expand All @@ -295,9 +301,12 @@ def get_weight_scaling_factor_2(module: nn.Module, weight_name: str = "weight")
if get_quantization_format(module) in [
QUANTIZATION_NVFP4,
QUANTIZATION_NVFP4_AWQ,
QUANTIZATION_W4A8_NVFP4_FP8,
]:
return NVFP4QTensor.get_weights_scaling_factor_2_from_quantizer(weight_quantizer)
elif get_quantization_format(module) == QUANTIZATION_W4A8_NVFP4_FP8:
# weight_scaling_factor_2 for w4a8 needs to be amax/448, so that the wsf is in range 448/6.
# This is because the kernel dequantizes weight to fp8, which is in range 448.
return weight_quantizer._amax.float() / 448.0

# SequentialQuantizer is required
if not isinstance(weight_quantizer, SequentialQuantizer) or not weight_quantizer[-1].is_enabled:
Expand Down