Add 2d-2d support to MXFP8 Grouped GEMM (#4816)

Summary:
X-link: facebookresearch/FBGEMM#1846


## MXFP8 grouped GEMM updates to (1) handle 2d-2d case, and (2) have a PyTorch compliant API

- Add support for 2d-2d inputs with dynamic groups along K dimension
- Added tests to ensure correct numerics for both 2d-2d and 2d-3d cases, with randomly group sizes
- Add benchmarks for both 2d-3d and 2d-2d cases

Reviewed By: ngimel, cthi

Differential Revision: D81362680

Author: danielvegamyhre

fbgemm_gpu/experimental/gen_ai/bench/quantize_ops.py

@@ -2916,78 +2916,194 @@ def cuda(self) -> bool:
 
 
 @register_quantize_op
-class MXFP8StackedGroupedGemm(QuantizeOpBase):
+class MXFP8GroupedGemm2d3d(QuantizeOpBase):
     """
-    MXFP8 grouped matmul with blockwise scaling and stacked inputs.
+    MXFP8 grouped GEMM with 2D inputs and 3D weights.
     """
 
     def preprocess(self, x, w):
-        m_values = [i.shape[0] for i in x]
-        m_sizes = torch.tensor(m_values).to(dtype=torch.int64, device=x[0].device)
+        assert isinstance(x, list)
+        assert isinstance(w, list)
+        x = torch.cat(x, dim=0).contiguous()  # (G * M, K)
+        w = torch.stack(w, dim=0).contiguous()  # (G, N, K)
+        return x, w
+
+    def quantize(self, x, w):
+        block_size = 32
+        G, N, K = w.shape
+        total_M = x.shape[0]
+        group_size = total_M // G
+        input_group_end_offsets = torch.arange(
+            group_size, total_M + 1, group_size, dtype=torch.int32, device=x.device
+        )
+
+        # For each constituent 2d subtensor in the 3d weights, quantize and convert scale to blocked format separately,
+        # as they each used for independent gemm in the grouped gemm.
         wq_list = []
         w_scale_list = []
-        for i in range(m_sizes.shape[0]):
+        for i in range(G):
             w_scale, wq = to_mxfp8(w[i])
             w_scale = _to_blocked(w_scale)
             wq_list.append(wq)
             w_scale_list.append(w_scale)
         wq = torch.stack(wq_list, dim=0).contiguous()
         w_scale = torch.stack(w_scale_list, dim=0).contiguous()
-        return x, wq, w_scale, m_sizes
 
-    def quantize(self, x, wq, w_scale, m_sizes):
-        starting_row_after_padding_list = [0]
+        # For each group along `total_M` in the 2D tensor, quantize and convert scale to blocked format separately,
+        # as they each used for independent gemm in the grouped gemm.
         xq_list = []
         x_scale_list = []
-        for i in range(m_sizes.shape[0]):
-            scale_slice = x[i]
-            if m_sizes[i].item() != 0:
-                x_scale, xq = to_mxfp8(scale_slice)
+        for i in range(G):
+            prev_group_end = 0 if i == 0 else input_group_end_offsets[i - 1]
+            curr_group_end = input_group_end_offsets[i]
+            group_size = curr_group_end - prev_group_end
+            if group_size > 0:
+                x_slice = x[prev_group_end:curr_group_end, :]
+                x_scale, xq = to_mxfp8(x_slice)
                 x_scale = _to_blocked(x_scale)
                 xq_list.append(xq)
                 x_scale_list.append(x_scale)
-                starting_row_after_padding_list.append(
-                    starting_row_after_padding_list[i]
-                    + x_scale.numel() // (x[0].shape[1] // 32)
-                )
-            else:
-                starting_row_after_padding_list.append(
-                    starting_row_after_padding_list[i]
-                )
         xq = torch.cat(xq_list, dim=0).contiguous()
         x_scale = torch.cat(x_scale_list, dim=0).contiguous()
-        x_scale = x_scale.reshape(-1, x[0].shape[-1] // 32)
+        x_scale = x_scale.reshape(-1, K // block_size)
         xq = xq.view(-1, xq.shape[-1])
-        return (
+        return xq, wq, x_scale, w_scale, input_group_end_offsets
+
+    def compute(self, xq, wq, x_scale, w_scale, input_group_end_offsets):
+        return torch.ops.fbgemm.mx8mx8bf16_grouped_mm(
             xq,
-            wq,
+            wq.transpose(-2, -1),
             x_scale,
             w_scale,
-            m_sizes,
-            torch.tensor(starting_row_after_padding_list, device=xq.device),
+            input_group_end_offsets,
         )
 
-    def compute(self, xq, wq, x_scale, w_scale, m_sizes, starting_row_after_padding):
-        return torch.ops.fbgemm.mx8mx8bf16_grouped_stacked(
+    def quantize_and_compute(self, x, w):
+        xq, wq, x_scale, w_scale, input_group_end_offsets = self.quantize(x, w)
+        return self.compute(
             xq,
             wq,
             x_scale,
             w_scale,
-            m_sizes,
-            starting_row_after_padding=starting_row_after_padding,
+            input_group_end_offsets,
         )
 
-    def quantize_and_compute(self, x, w):
-        xq, wq, x_scale, w_scale, m_sizes, starting_row_after_padding = self.quantize(
-            x, w
+    @property
+    def name(self) -> str:
+        return "cutlass_mx8mx8bf16_grouped_mm_2d_3d"
+
+    @property
+    def hip(self) -> bool:
+        return False
+
+    @property
+    def cuda(self) -> bool:
+        return True
+
+
+@register_quantize_op
+class MXFP8GroupedGemm2d2d(QuantizeOpBase):
+    """
+    MXFP8 grouped GEMM with 2D inputs and 3D weights.
+    """
+
+    def preprocess(self, x, w):
+        assert isinstance(x, list)
+        assert isinstance(w, list)
+        G = len(x)
+        x = torch.cat(x, dim=1).contiguous()  # (M, total_K)
+        w = torch.cat(w, dim=1).contiguous()  # (N, total_K)
+        return x, w, G
+
+    def quantize(self, x, w, G):
+        # Simulate 2d-2d grouped gemm in backward pass `grad_weight = grad_output_t @ input`,
+        # where we use "K" as the contracting dim which has "G" groups.
+        M, total_K = x.shape
+        N, _ = w.shape
+        group_size = total_K // G
+        input_group_end_offsets = torch.arange(
+            group_size, total_K + 1, group_size, dtype=torch.int32, device=x.device
+        )
+
+        # Convert scales to blocked format.
+        x_list = []
+        w_list = []
+        x_blocked_scale_list = []
+        w_blocked_scale_list = []
+
+        def round_up(x: int, y: int) -> int:
+            return ((x + y - 1) // y) * y
+
+        for group_idx in range(G):
+            # to_mxfp8 per group
+            prev_group_end_offset = (
+                0 if group_idx == 0 else input_group_end_offsets[group_idx - 1]
+            )
+            curr_group_end_offset = input_group_end_offsets[group_idx]
+            group_size = curr_group_end_offset - prev_group_end_offset
+            if group_size > 0:
+                x_slice = x[
+                    :, prev_group_end_offset:curr_group_end_offset
+                ].contiguous()  # (M, K_group)
+                w_slice = w[
+                    :, prev_group_end_offset:curr_group_end_offset
+                ].contiguous()  # (N, K_group)
+                x_scale_slice, xq_slice = to_mxfp8(
+                    x_slice
+                )  # scale shape -> (M, K_group // 32)
+                w_scale_slice, wq_slice = to_mxfp8(
+                    w_slice
+                )  # scale shape -> (N, K_group // 32)
+                x_list.append(xq_slice)
+                w_list.append(wq_slice)
+
+                # Convert scales to blocked format.
+                x_scale_slice_blocked = _to_blocked(
+                    x_scale_slice
+                )  # (round_up(M, 128), round_up(K_group//32, 4))
+                w_scale_slice_blocked = _to_blocked(
+                    w_scale_slice
+                )  # (round_up(N, 128), round_up(K_group//32, 4))
+                x_blocked_scale_list.append(x_scale_slice_blocked)
+                w_blocked_scale_list.append(w_scale_slice_blocked)
+
+        # Assemble the full XQ and WQ
+        xq = torch.cat(x_list, dim=1).contiguous()
+        wq = torch.cat(w_list, dim=1).contiguous()
+
+        # Combine all XQ groups blocked scales into one tensor.
+        x_blocked_scales = torch.cat(x_blocked_scale_list, dim=0)
+        M_rounded = round_up(M, 128)
+        x_blocked_scales = x_blocked_scales.reshape(M_rounded, -1)
+
+        # Combine all WQ groups blocked scales into one tensor.
+        w_blocked_scales = torch.cat(w_blocked_scale_list, dim=0)
+        N_rounded = round_up(N, 128)
+        w_blocked_scales = w_blocked_scales.reshape(N_rounded, -1)
+        return xq, wq, x_blocked_scales, w_blocked_scales, input_group_end_offsets
+
+    def compute(self, xq, wq, x_scale, w_scale, input_group_end_offsets):
+        return torch.ops.fbgemm.mx8mx8bf16_grouped_mm(
+            xq,
+            wq.transpose(-2, -1),
+            x_scale,
+            w_scale,
+            input_group_end_offsets,
         )
+
+    def quantize_and_compute(self, x, w):
+        xq, wq, x_scale, w_scale, input_group_end_offsets = self.quantize(x, w)
         return self.compute(
-            xq, wq, x_scale, w_scale, m_sizes, starting_row_after_padding
+            xq,
+            wq,
+            x_scale,
+            w_scale,
+            input_group_end_offsets,
         )
 
     @property
     def name(self) -> str:
-        return "cutlass_mx8mx8bf16_grouped_stacked"
+        return "cutlass_mx8mx8bf16_grouped_mm_2d_2d"
 
     @property
     def hip(self) -> bool: