[Quantization] Remove FP4 emulation; Fall-back to marlin for device < 100 (vllm-project#19563)

Author: dsikka

tests/quantization/test_compressed_tensors.py

@@ -667,7 +667,13 @@ def check_model(model):
             qkv_proj = layer.self_attn.qkv_proj
             assert isinstance(qkv_proj.quant_method,
                               CompressedTensorsLinearMethod)
-            assert isinstance(qkv_proj.scheme, scheme)
+            if isinstance(qkv_proj.scheme, scheme) or isinstance(
+                    qkv_proj.scheme, CompressedTensorsW4A16Fp4
+            ) and not CompressedTensorsW4A4Fp4.cutlass_fp4_supported():
+                assert True
+            else:
+                raise AssertionError("FP4 Scheme Mismatch")
+
             assert qkv_proj.scheme.group_size == 16
 
         llm.apply_model(check_model)

vllm/model_executor/layers/quantization/compressed_tensors/compressed_tensors.py

@@ -374,7 +374,14 @@ def _get_scheme_from_parts(
 
         if is_activation_quantization_format(self.quant_format):
             if self._is_fp4a4_nvfp4(weight_quant, input_quant):
-                return CompressedTensorsW4A4Fp4()
+                if CompressedTensorsW4A4Fp4.cutlass_fp4_supported():
+                    return CompressedTensorsW4A4Fp4()
+                else:
+                    logger.warning_once(
+                        "Current platform does not support cutlass NVFP4."
+                        " Running CompressedTensorsW4A16Fp4.")
+                    return CompressedTensorsW4A16Fp4(
+                        has_input_global_scale=True)
 
             if self._is_fp8_w8a8(weight_quant, input_quant):
                 is_fp8_w8a8_supported = self._check_scheme_supported(

vllm/model_executor/layers/quantization/compressed_tensors/schemes/compressed_tensors_w4a16_nvfp4.py

@@ -18,7 +18,8 @@
 
 class CompressedTensorsW4A16Fp4(CompressedTensorsScheme):
 
-    def __init__(self):
+    def __init__(self, has_input_global_scale: bool = False):
+        self.has_input_global_scale = has_input_global_scale
         self.group_size = 16
 
     @classmethod
@@ -64,6 +65,13 @@ def create_weights(self, layer: torch.nn.Module,
 
         layer.register_parameter("weight_scale", weight_scale)
 
+        if self.has_input_global_scale:
+            input_global_scale = PerTensorScaleParameter(
+                data=torch.empty(len(output_partition_sizes),
+                                 dtype=torch.float32),
+                weight_loader=weight_loader)
+            layer.register_parameter("input_global_scale", input_global_scale)
+
     def process_weights_after_loading(self, layer) -> None:
         # Process parameters for marlin repacking
 
@@ -77,6 +85,10 @@ def process_weights_after_loading(self, layer) -> None:
             requires_grad=False)
         del layer.weight_global_scale
 
+        if self.has_input_global_scale:
+            layer.input_global_scale = torch.nn.Parameter(
+                layer.input_global_scale.data, requires_grad=False)
+
         prepare_fp4_layer_for_marlin(layer)
 
     def apply_weights(self,

vllm/model_executor/layers/quantization/compressed_tensors/schemes/compressed_tensors_w4a4_nvfp4.py

@@ -9,8 +9,6 @@
 from vllm.logger import init_logger
 from vllm.model_executor.layers.quantization.compressed_tensors.schemes import (
     CompressedTensorsScheme)
-from vllm.model_executor.layers.quantization.utils.nvfp4_emulation_utils import (  # noqa: E501
-    dequantize_to_dtype, ref_nvfp4_quant)
 from vllm.model_executor.parameter import (GroupQuantScaleParameter,
                                            ModelWeightParameter,
                                            PerTensorScaleParameter)
@@ -21,53 +19,23 @@
 __all__ = ["CompressedTensorsW4A4Fp4"]
 
 
-def cutlass_fp4_supported() -> bool:
-    if not current_platform.is_cuda():
-        return False
-    capability_tuple = current_platform.get_device_capability()
-    capability = -1 if capability_tuple is None else capability_tuple.to_int()
-    return cutlass_scaled_mm_supports_fp4(capability)
-
-
 class CompressedTensorsW4A4Fp4(CompressedTensorsScheme):
 
     def __init__(self):
         self.group_size = 16
-        self.cutlass_nvfp4_supported = cutlass_fp4_supported()
-        if not self.cutlass_nvfp4_supported:
-            logger.warning("Current platform does not support cutlass NVFP4."
-                           " Running emulations.")
 
     @classmethod
     def get_min_capability(cls) -> int:
-        # dont restrict as emulations
-        return 80
-
-    def run_nvfp4_emulations(self, x: torch.Tensor, layer):
-        x_m, x_k = x.shape
-        output_dtype = x.dtype
-
-        # quantize input to (FP4 and interleaved block scale)
-        x_fp4, x_blockscale = ref_nvfp4_quant(x, layer.input_global_scale,
-                                              self.group_size)
+        return 100
 
-        # dequantize input
-        x_fp4 = x_fp4.reshape(x_m, x_k // self.group_size, self.group_size)
-        x_blockscale = x_blockscale.unsqueeze(-1) / layer.input_global_scale
-        x_dq = (x_fp4 * x_blockscale).reshape(x_m, x_k).to(output_dtype)
-        del x_fp4, x_blockscale
-
-        # dequantize weight
-        w_fp4 = layer.weight.data.view(torch.uint8)
-        w_blockscale = layer.weight_scale_swizzled.data
-        w_global_scale = layer.weight_global_scale
-        w_dq = dequantize_to_dtype(w_fp4, w_blockscale, w_global_scale,
-                                   output_dtype, x.device, self.group_size)
-
-        # matmul
-        out = torch.matmul(x_dq, w_dq.t())
-        del w_dq, x_dq
-        return out
+    @classmethod
+    def cutlass_fp4_supported(cls) -> bool:
+        if not current_platform.is_cuda():
+            return False
+        capability_tuple = current_platform.get_device_capability()
+        capability = -1 if capability_tuple is None else capability_tuple.to_int(  # noqa: E501
+        )
+        return cutlass_scaled_mm_supports_fp4(capability)
 
     def create_weights(self, layer: torch.nn.Module,
                        output_partition_sizes: list[int],
@@ -152,27 +120,24 @@ def process_weights_after_loading(self, layer) -> None:
         # required by cutlass kernel; need Parameter, not ModelWeightParameter
         layer.weight = Parameter(layer.weight_packed.data, requires_grad=False)
 
-        if self.cutlass_nvfp4_supported:
-            layer.alpha = Parameter(layer.input_global_scale *
-                                    layer.weight_global_scale,
-                                    requires_grad=False)
+        layer.alpha = Parameter(layer.input_global_scale *
+                                layer.weight_global_scale,
+                                requires_grad=False)
 
     def apply_weights(self,
                       layer: torch.nn.Module,
                       x: torch.Tensor,
                       bias: Optional[torch.Tensor] = None) -> torch.Tensor:
 
-        if self.cutlass_nvfp4_supported:
-            output_dtype = x.dtype
-            output_shape = [x.shape[0], layer.weight.shape[0]]
+        output_dtype = x.dtype
+        output_shape = [x.shape[0], layer.weight.shape[0]]
 
-            # quantize BF16 or FP16 to (FP4 and interleaved block scale)
-            x_fp4, x_blockscale = scaled_fp4_quant(x, layer.input_global_scale)
+        # quantize BF16 or FP16 to (FP4 and interleaved block scale)
+        x_fp4, x_blockscale = scaled_fp4_quant(x, layer.input_global_scale)
 
-            out = cutlass_scaled_fp4_mm(x_fp4, layer.weight, x_blockscale,
-                                        layer.weight_scale_swizzled,
-                                        1 / layer.alpha, output_dtype)
-            if bias is not None:
-                out = out + bias
-            return out.view(*output_shape)
-        return self.run_nvfp4_emulations(x, layer)
+        out = cutlass_scaled_fp4_mm(x_fp4, layer.weight, x_blockscale,
+                                    layer.weight_scale_swizzled,
+                                    1 / layer.alpha, output_dtype)
+        if bias is not None:
+            out = out + bias
+        return out.view(*output_shape)

vllm/model_executor/layers/quantization/utils/nvfp4_emulation_utils.py

@@ -102,3 +102,32 @@ def ref_nvfp4_quant(x, global_scale, block_size):
     clipped_x = torch.clamp(scaled_x, -6.0, 6.0).reshape(m, n)
     # both outputs are float32
     return cast_to_fp4(clipped_x), scale.squeeze(-1)
+
+
+def run_nvfp4_emulations(x: torch.Tensor, input_global_scale: torch.Tensor,
+                         weight: torch.Tensor,
+                         weight_scale_swizzled: torch.Tensor,
+                         weight_global_scale: torch.Tensor):
+    group_size = 16
+    x_m, x_k = x.shape
+    output_dtype = x.dtype
+
+    # quantize input to (FP4 and interleaved block scale)
+    x_fp4, x_blockscale = ref_nvfp4_quant(x, input_global_scale, group_size)
+
+    # dequantize input
+    x_fp4 = x_fp4.reshape(x_m, x_k // group_size, group_size)
+    x_blockscale = x_blockscale.unsqueeze(-1) / input_global_scale
+    x_dq = (x_fp4 * x_blockscale).reshape(x_m, x_k).to(output_dtype)
+    del x_fp4, x_blockscale
+
+    # dequantize weight
+    w_fp4 = weight.data.view(torch.uint8)
+    w_dq = dequantize_to_dtype(w_fp4, weight_scale_swizzled.data,
+                               weight_global_scale, output_dtype, x.device,
+                               group_size)
+
+    # matmul
+    out = torch.matmul(x_dq, w_dq.t())
+    del w_dq, x_dq
+    return out