Support w8a8 int8 quantization config (#2881)

python/sglang/srt/configs/model_config.py

@@ -223,7 +223,11 @@ class ModelConfig:
             "compressed_tensors",
             "compressed-tensors",
             "experts_int8",
+            "w8a8_int8",
         ]
+        compatible_quantization_methods = {
+            "w8a8_int8": ["compressed-tensors", "compressed_tensors"]
+        }
         if self.quantization is not None:
             self.quantization = self.quantization.lower()
 
@@ -247,12 +251,17 @@ class ModelConfig:
             if self.quantization is None:
                 self.quantization = quant_method
             elif self.quantization != quant_method:
-                raise ValueError(
-                    "Quantization method specified in the model config "
-                    f"({quant_method}) does not match the quantization "
-                    f"method specified in the `quantization` argument "
-                    f"({self.quantization})."
-                )
+                if (
+                    self.quantization not in compatible_quantization_methods
+                    or quant_method
+                    not in compatible_quantization_methods[self.quantization]
+                ):
+                    raise ValueError(
+                        "Quantization method specified in the model config "
+                        f"({quant_method}) does not match the quantization "
+                        f"method specified in the `quantization` argument "
+                        f"({self.quantization})."
+                    )
 
         if self.quantization is not None:
             if self.quantization not in supported_quantization:

python/sglang/srt/layers/quantization/__init__.py

@@ -23,6 +23,7 @@ from vllm.model_executor.layers.quantization.tpu_int8 import Int8TpuConfig
 from sglang.srt.layers.quantization.base_config import QuantizationConfig
 from sglang.srt.layers.quantization.fp8 import Fp8Config
 from sglang.srt.layers.quantization.modelopt_quant import ModelOptFp8Config
+from sglang.srt.layers.quantization.w8a8_int8 import W8A8Int8Config
 
 QUANTIZATION_METHODS: Dict[str, Type[QuantizationConfig]] = {
     "aqlm": AQLMConfig,
@@ -42,6 +43,7 @@ QUANTIZATION_METHODS: Dict[str, Type[QuantizationConfig]] = {
     "bitsandbytes": BitsAndBytesConfig,
     "qqq": QQQConfig,
     "experts_int8": ExpertsInt8Config,
+    "w8a8_int8": W8A8Int8Config,
 }
 
 

python/sglang/srt/layers/quantization/w8a8_int8.py

@@ -0,0 +1,117 @@
+from typing import Any, Dict, List, Optional
+
+import torch
+
+from sglang.srt.utils import is_cuda_available
+
+is_cuda = is_cuda_available()
+if is_cuda:
+    from sgl_kernel import int8_scaled_mm
+
+from torch.nn.parameter import Parameter
+
+from sglang.srt.layers.linear import LinearMethodBase
+from sglang.srt.layers.parameter import ChannelQuantScaleParameter, ModelWeightParameter
+from sglang.srt.layers.quantization.base_config import (
+    QuantizationConfig,
+    QuantizeMethodBase,
+)
+from sglang.srt.layers.quantization.int8_kernel import per_token_quant_int8
+
+
+class W8A8Int8Config(QuantizationConfig):
+    """Config class for W8A8 Int8 Quantization.
+
+    - Weight: static, per-channel, symmetric
+    - Activation: dynamic, per-token, symmetric
+    """
+
+    def __init__(self):
+        pass
+
+    @classmethod
+    def get_supported_act_dtypes(cls) -> List[torch.dtype]:
+        return [torch.float16, torch.bfloat16]
+
+    @classmethod
+    def get_min_capability(cls) -> int:
+        return 75
+
+    @classmethod
+    def get_name(self) -> str:
+        return "w8a8_int8"
+
+    @classmethod
+    def get_config_filenames(cls) -> List[str]:
+        return []
+
+    @classmethod
+    def from_config(cls, config: Dict[str, Any]) -> "W8A8Int8Config":
+        return cls()
+
+    def get_quant_method(
+        self,
+        layer: torch.nn.Module,
+        prefix: str,
+    ) -> Optional["QuantizeMethodBase"]:
+        from vllm.model_executor.layers.linear import LinearBase
+
+        if isinstance(layer, LinearBase):
+            return W8A8Int8LinearMethod(self)
+        return None
+
+    def get_scaled_act_names(self) -> List[str]:
+        return []
+
+
+class W8A8Int8LinearMethod(LinearMethodBase):
+
+    def __init__(self, quantization_config: W8A8Int8Config):
+        self.quantization_config = quantization_config
+
+    def process_weights_after_loading(self, layer: torch.nn.Module) -> None:
+        layer.weight = Parameter(layer.weight.t(), requires_grad=False)
+        layer.weight_scale = Parameter(layer.weight_scale.data, requires_grad=False)
+
+    def create_weights(
+        self,
+        layer: torch.nn.Module,
+        input_size_per_partition: int,
+        output_partition_sizes: List[int],
+        input_size: int,
+        output_size: int,
+        params_dtype: torch.dtype,
+        **extra_weight_attrs
+    ):
+
+        weight_loader = extra_weight_attrs.get("weight_loader")
+        self.logical_widths = output_partition_sizes
+
+        weight = ModelWeightParameter(
+            data=torch.empty(
+                sum(output_partition_sizes), input_size_per_partition, dtype=torch.int8
+            ),
+            input_dim=1,
+            output_dim=0,
+            weight_loader=weight_loader,
+        )
+        layer.register_parameter("weight", weight)
+
+        weight_scale = ChannelQuantScaleParameter(
+            data=torch.empty((sum(output_partition_sizes), 1), dtype=torch.float32),
+            output_dim=0,
+            weight_loader=weight_loader,
+        )
+        layer.register_parameter("weight_scale", weight_scale)
+
+    def apply(
+        self,
+        layer: torch.nn.Module,
+        x: torch.Tensor,
+        bias: Optional[torch.Tensor] = None,
+    ):
+        x_q, x_scale = per_token_quant_int8(x)
+
+        return int8_scaled_mm(
+            x_q, layer.weight, x_scale, layer.weight_scale, out_dtype=x.dtype, bias=bias
+        )

python/sglang/srt/server_args.py

@@ -378,6 +378,7 @@ class ServerArgs:
                 "bitsandbytes",
                 "gguf",
                 "modelopt",
+                "w8a8_int8",
             ],
             help="The quantization method.",
         )