Add MXFP8 grouped GEMM (E4M3) for routed-expert MoE training

README.md

@@ -20,6 +20,7 @@ Training-oriented kernels and schemes include:
 
 - **[Blockwise FP8](alto/kernels/blockwise_fp8)** — linear, grouped GEMM, and FlashAttention.
 - **[MXFP4](alto/kernels/fp4/mxfp4)** — linear, grouped GEMM, and FlashAttention.
+- **[MXFP8](alto/kernels/mxfp8)** — linear and grouped GEMM (block-scaled E4M3, with E5M2 reserved for gradients).
 - **[NVFP4](alto/kernels/fp4/nvfp4)** — linear and grouped GEMM, using an E4M3 inner-block scale with an optional two-level (tensorwise) outer scale.
 
 Techniques used to narrow the gap versus BF16 include:

alto/kernels/dispatch/tensor.py

@@ -21,6 +21,7 @@
 from alto.kernels.fp4.nvfp4.nvfp_grouped_gemm.functional import (
     _quantize_then_nvfp4_scaled_grouped_mm,)
 from alto.kernels.mxfp8.mxfp8_linear import _to_mxfp8_then_scaled_mm
+from alto.kernels.mxfp8.mxfp8_grouped_gemm import _quantize_then_mxfp8_scaled_grouped_mm
 from .config import TrainingOpConfig
 
 aten = torch.ops.aten
@@ -406,8 +407,35 @@ class MXFP8TrainingWeightWrapperTensor(TrainingWeightWrapperBaseTensor):
     @classmethod
     def __torch_function__(cls, func, types, args, kwargs={}):
         if func.__name__ == "_grouped_mm":
-            raise NotImplementedError("MXFP8 _grouped_mm is not supported by this dispatch path; "
-                                      "restrict MXFP8 schemes to Linear targets.")
+            # Routed-expert MoE path: 2d activations x 3d weights with offsets.
+            A, B = args[0], args[1]
+            bias = kwargs.get("bias", None)
+            offs = kwargs.get("offs", None)
+
+            assert not isinstance(A, cls), f"A should not be a {cls.__name__}"
+            assert isinstance(B, cls), f"B should be a {cls.__name__}"
+            assert A.ndim == 2 and B.ndim == 3 and offs is not None, (
+                "Only 2d x 3d with offsets is supported for MXFP8 grouped_mm"
+            )
+            assert bias is None, "Bias is not supported for grouped_mm"
+
+            config = B.config
+            assert config.precision == "mxfp8_e4m3", (
+                "MXFP8 grouped_mm V1 supports only mxfp8_e4m3; "
+                f"got {config.precision} (e5m2 grouped path is not yet validated)"
+            )
+            assert not config.use_hadamard and not config.use_dge, (
+                "MXFP8 grouped_mm V1 does not support Hadamard or DGE options."
+            )
+
+            return _quantize_then_mxfp8_scaled_grouped_mm(
+                A,
+                B,
+                offs=offs,
+                use_2dblock_x=config.use_2dblock_x,
+                use_2dblock_w=config.use_2dblock_w,
+                use_sr_grad=config.use_sr_grad,
+            )
 
         if func.__name__ in gemm_ops:
             trans_b = func.__name__ == "linear"

alto/kernels/mxfp8/mxfp8_grouped_gemm/__init__.py

@@ -0,0 +1,9 @@
+# Copyright (c) 2026 Advanced Micro Devices, Inc.
+# SPDX-License-Identifier: MIT
+
+from alto.kernels.mxfp8.mxfp8_grouped_gemm.functional import (
+    mxfp8_grouped_gemm,
+    _quantize_then_mxfp8_scaled_grouped_mm,
+)
+
+__all__ = ["mxfp8_grouped_gemm", "_quantize_then_mxfp8_scaled_grouped_mm"]

alto/kernels/mxfp8/mxfp8_grouped_gemm/autotune.py

@@ -0,0 +1,51 @@
+# Copyright (c) 2026 Advanced Micro Devices, Inc.
+# SPDX-License-Identifier: MIT
+"""Autotune configs for mxfp8 grouped GEMM.
+
+v1 keeps a single conservative config:
+- BLOCK_SIZE_K == QUANT_BLOCK_SIZE (=32) so each tl.dot_scaled call covers
+  exactly one mx scale group; this matches the numerical contract validated
+  by alto/kernels/mxfp8/mxfp8_linear.py.
+- BSM=BSN=128 matches mxfp4 grouped GEMM's default tile.
+Wider autotune is deferred to v2.
+"""
+
+import triton
+
+ALIGN_SIZE_M = 128  # token routing alignment; tokens routed to the same expert must form contiguous blocks of this size
+
+STANDARD_CONFIGS = [
+    triton.Config(
+        {
+            "BLOCK_SIZE_M": 128,
+            "BLOCK_SIZE_N": 128,
+            "BLOCK_SIZE_K": 32,
+        },
+        num_stages=2,
+        num_warps=4,
+    ),
+]
+
+DGRAD_CONFIGS = [
+    triton.Config(
+        {
+            "BLOCK_SIZE_M": 128,
+            "BLOCK_SIZE_N": 32,   # dgrad reduces over N; keep one MX scale group per dot_scaled
+            "BLOCK_SIZE_K": 32,
+        },
+        num_stages=2,
+        num_warps=4,
+    ),
+]
+
+WGRAD_CONFIGS = [
+    triton.Config(
+        {
+            "BLOCK_SIZE_M": 32,   # wgrad reduces over M; keep one MX scale group per dot_scaled
+            "BLOCK_SIZE_N": 128,
+            "BLOCK_SIZE_K": 32,
+        },
+        num_stages=2,
+        num_warps=4,
+    ),
+]