gptq marlin quantization support for fused moe with lora (#30254)

Signed-off-by: Bhanu068 <voutharoja.bhanu06@gmail.com>

vllm/model_executor/layers/fused_moe/config.py

@@ -543,6 +543,42 @@ def int8_w8a8_moe_quant_config(
     )
 
 
+def gptq_marlin_moe_quant_config(
+    w1_scale: torch.Tensor,
+    w2_scale: torch.Tensor,
+    weight_bits: int,
+    group_size: int,
+    w1_zp: torch.Tensor | None = None,
+    w2_zp: torch.Tensor | None = None,
+    w1_bias: torch.Tensor | None = None,
+    w2_bias: torch.Tensor | None = None,
+):
+    """
+    Construct a quant config for gptq marlin quantization.
+    """
+    from vllm.model_executor.layers.quantization.utils.quant_utils import GroupShape
+
+    w_shape = None if group_size == -1 else GroupShape(row=1, col=group_size)
+
+    # Activations are NOT quantized for GPTQ (fp16/bf16)
+    a_shape = w_shape  # Same as weight shape for alignment
+
+    # Determine weight dtype
+    if weight_bits == 4:
+        weight_dtype = "int4"
+    elif weight_bits == 8:
+        weight_dtype = torch.int8
+    else:
+        raise ValueError(f"Unsupported weight_bits: {weight_bits}")
+
+    return FusedMoEQuantConfig(
+        _a1=FusedMoEQuantDesc(dtype=None, shape=a_shape),
+        _a2=FusedMoEQuantDesc(dtype=None, shape=a_shape),
+        _w1=FusedMoEQuantDesc(weight_dtype, w_shape, w1_scale, None, w1_zp, w1_bias),
+        _w2=FusedMoEQuantDesc(weight_dtype, w_shape, w2_scale, None, w2_zp, w2_bias),
+    )
+
+
 def mxfp4_w4a16_moe_quant_config(
     w1_scale: Union[torch.Tensor, "PrecisionConfig"],
     w2_scale: Union[torch.Tensor, "PrecisionConfig"],

vllm/model_executor/layers/quantization/gptq_marlin.py

@@ -732,6 +732,14 @@ class GPTQMarlinMoEMethod(FusedMoEMethodBase):
             is_a_8bit=is_a_8bit,
         )
         replace_parameter(layer, "w2_qweight", marlin_w2_qweight)
+
+        # The modular kernel expects w13_weight and w2_weight,
+        # but GPTQ uses w13_qweight and w2_qweight
+        # Alias for modular kernel
+        layer.w13_weight = layer.w13_qweight
+        # Alias for modular kernel
+        layer.w2_weight = layer.w2_qweight
+
         # Repack scales
         marlin_w13_scales = marlin_moe_permute_scales(
             s=layer.w13_scales,
@@ -782,7 +790,107 @@ class GPTQMarlinMoEMethod(FusedMoEMethodBase):
     def get_fused_moe_quant_config(
         self, layer: torch.nn.Module
     ) -> FusedMoEQuantConfig | None:
-        return None
+        from vllm.model_executor.layers.fused_moe.config import (
+            gptq_marlin_moe_quant_config,
+        )
+
+        return gptq_marlin_moe_quant_config(
+            w1_scale=layer.w13_scales,
+            w2_scale=layer.w2_scales,
+            weight_bits=self.quant_config.weight_bits,
+            group_size=self.quant_config.group_size,
+            w1_zp=getattr(layer, "w13_qzeros", None)
+            if not self.quant_config.is_sym
+            else None,
+            w2_zp=getattr(layer, "w2_qzeros", None)
+            if not self.quant_config.is_sym
+            else None,
+            w1_bias=getattr(layer, "w13_bias", None),
+            w2_bias=getattr(layer, "w2_bias", None),
+        )
+
+    def select_gemm_impl(
+        self,
+        prepare_finalize,
+        layer: torch.nn.Module,
+    ):
+        """
+        Select the GEMM implementation for GPTQ-Marlin MoE.
+
+        Returns MarlinExperts configured for GPTQ quantization.
+        This is ONLY used when LoRA is enabled.
+        Without LoRA, GPTQ uses its own apply() method.
+        """
+        # Only use modular kernels when LoRA is enabled
+        # Without LoRA, GPTQ's own apply() method works fine and is more efficient
+        if not self.moe.is_lora_enabled:
+            raise NotImplementedError(
+                "GPTQ-Marlin uses its own apply() method when LoRA is not enabled. "
+                "Modular kernels are only used for LoRA support."
+            )
+
+        # The modular marlin kernels do not support 8-bit weights.
+        if self.quant_config.weight_bits == 8:
+            raise NotImplementedError(
+                "GPTQ-Marlin kernel does not support 8-bit weights."
+            )
+
+        from vllm.model_executor.layers.fused_moe import modular_kernel as mk
+        from vllm.model_executor.layers.fused_moe.fused_marlin_moe import (
+            BatchedMarlinExperts,
+            MarlinExperts,
+        )
+
+        # Ensure quant config is initialized
+        assert self.moe_quant_config is not None, (
+            "moe_quant_config must be initialized before select_gemm_impl"
+        )
+
+        w13_g_idx = (
+            getattr(layer, "w13_g_idx", None) if self.quant_config.desc_act else None
+        )
+        w2_g_idx = (
+            getattr(layer, "w2_g_idx", None) if self.quant_config.desc_act else None
+        )
+        w13_g_idx_sort_indices = (
+            getattr(layer, "w13_g_idx_sort_indices", None)
+            if self.quant_config.desc_act
+            else None
+        )
+        w2_g_idx_sort_indices = (
+            getattr(layer, "w2_g_idx_sort_indices", None)
+            if self.quant_config.desc_act
+            else None
+        )
+
+        # Check if using batched expert format (for Expert Parallelism)
+        if (
+            prepare_finalize.activation_format
+            == mk.FusedMoEActivationFormat.BatchedExperts
+        ):
+            # For batched format, use BatchedMarlinExperts
+            max_num_tokens_per_rank = prepare_finalize.max_num_tokens_per_rank()
+            assert max_num_tokens_per_rank is not None
+            return BatchedMarlinExperts(
+                max_num_tokens=max_num_tokens_per_rank,
+                num_dispatchers=prepare_finalize.num_dispatchers(),
+                quant_config=self.moe_quant_config,
+                w13_g_idx=w13_g_idx,
+                w2_g_idx=w2_g_idx,
+                w13_g_idx_sort_indices=w13_g_idx_sort_indices,
+                w2_g_idx_sort_indices=w2_g_idx_sort_indices,
+                is_k_full=self.is_k_full,
+            )
+        else:
+            # Standard Marlin experts for GPTQ
+            return MarlinExperts(
+                quant_config=self.moe_quant_config,
+                w13_g_idx=w13_g_idx,
+                w2_g_idx=w2_g_idx,
+                w13_g_idx_sort_indices=w13_g_idx_sort_indices,
+                w2_g_idx_sort_indices=w2_g_idx_sort_indices,
+                is_k_full=self.is_k_full,
+            )
 
     def apply(
         self,