[mxfp8 moe training] add triton kernel for mxfp8 dequantization (#3195)

danielvegamyhre · web-flow · commit 7537d99fd3fd · 2025-10-28T12:36:12.000-07:00
diff --git a/benchmarks/prototype/moe_training/mxfp8/bench_dequantize.py b/benchmarks/prototype/moe_training/mxfp8/bench_dequantize.py
@@ -0,0 +1,170 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+# All rights reserved.
+#
+# This source code is licensed under the BSD 3-Clause license found in the
+# LICENSE file in the root directory of this source tree.
+# this benchmarking script is a modified version of the original script from: https://github.com/drisspg/transformer_nuggets/blob/main/transformer_nuggets/utils/benchmark.py
+
+from dataclasses import dataclass
+from typing import List
+
+import torch
+from tabulate import tabulate
+from tqdm import tqdm
+
+from benchmarks.utils import benchmark_cuda_function_in_microseconds
+from torchao.prototype.mx_formats.kernels import triton_mxfp8_dequant_dim0
+from torchao.prototype.mx_formats.mx_tensor import to_dtype, to_mx
+
+device = torch.device("cuda")
+
+# Needed since changing args to function causes recompiles
+torch._dynamo.config.cache_size_limit = 1000
+
+
+@dataclass(frozen=True)
+class ExperimentConfig:
+    input_shape: tuple[int]
+
+
+@dataclass(frozen=True)
+class ExperimentResult:
+    # time
+    torch_us: float
+    triton_us: float
+    torch_gbps: float
+    triton_gbps: float
+
+
+@dataclass(frozen=True)
+class Experiment:
+    config: ExperimentConfig
+    result: ExperimentResult
+
+
+def get_configs() -> List[ExperimentConfig]:
+    input_shapes = [
+        # (local_batch_size, seq_len, dim)
+        (1, 8192, 7168),
+        (2, 8192, 7168),
+        (4, 8192, 7168),
+        (8, 8192, 7168),
+    ]
+    configs = []
+    for shape in input_shapes:
+        configs.append(
+            ExperimentConfig(
+                input_shape=shape,
+            )
+        )
+    return configs
+
+
+def run_experiment(config: ExperimentConfig) -> ExperimentResult:
+    block_size = 32
+    input_shape = config.input_shape
+    input_tensor = torch.randn(
+        *input_shape,
+        dtype=torch.bfloat16,
+        device=device,
+    )
+
+    e8m0_scales, e4m3_data = to_mx(input_tensor, torch.float8_e4m3fn, block_size)
+
+    # Bench torch dequant
+    to_dtype_c = torch.compile(to_dtype)
+    elem_dtype, target_dtype = torch.float8_e4m3fn, torch.bfloat16
+    torch_output = to_dtype_c(
+        e4m3_data,
+        e8m0_scales,
+        elem_dtype,
+        block_size,
+        target_dtype,
+    )
+    torch_us = benchmark_cuda_function_in_microseconds(
+        to_dtype_c,
+        e4m3_data,
+        e8m0_scales,
+        elem_dtype,
+        block_size,
+        target_dtype,
+    )
+
+    # Bench triton kernel
+    _ = triton_mxfp8_dequant_dim0(
+        e4m3_data,
+        e8m0_scales,
+        target_dtype,
+        block_size,
+    )
+    triton_us = benchmark_cuda_function_in_microseconds(
+        triton_mxfp8_dequant_dim0,
+        e4m3_data,
+        e8m0_scales,
+        target_dtype,
+        block_size,
+    )
+
+    # mem bw calculations
+    bytes_per_input_el = torch.finfo(elem_dtype).bits / 8
+    bytes_per_output_el = torch.finfo(target_dtype).bits / 8
+    bytes_per_scale_el = torch.finfo(torch.float8_e8m0fnu).bits / 8
+
+    read_bytes = (
+        e4m3_data.numel() * bytes_per_input_el
+        + e8m0_scales.numel() * bytes_per_scale_el
+    )
+    write_bytes = torch_output.numel() * bytes_per_output_el
+
+    torch_gbps = ((read_bytes + write_bytes) / 1e9) / (torch_us / 1e6)
+    triton_gbps = ((read_bytes + write_bytes) / 1e9) / (triton_us / 1e6)
+
+    return ExperimentResult(
+        torch_us=torch_us,
+        triton_us=triton_us,
+        triton_gbps=triton_gbps,
+        torch_gbps=torch_gbps,
+    )
+
+
+def print_results(experiments: List[Experiment]):
+    headers = [
+        "input_shape",
+        "torch_us",
+        "triton_us",
+        "torch_gbps",
+        "triton_gbps",
+        "triton_speedup",
+    ]
+    rows = []
+    for experiment in experiments:
+        triton_speedup = round(
+            experiment.result.torch_us / experiment.result.triton_us, 3
+        )
+        rows.append(
+            [
+                str(experiment.config.input_shape),
+                experiment.result.torch_us,
+                experiment.result.triton_us,
+                round(experiment.result.torch_gbps, 3),
+                round(experiment.result.triton_gbps, 3),
+                f"{triton_speedup}x",
+            ]
+        )
+    print(tabulate(rows, headers=headers))
+
+
+def main():
+    torch.random.manual_seed(123)
+    configs = get_configs()
+    results = []
+    for config in tqdm(configs):
+        result = run_experiment(config)
+        results.append(Experiment(config=config, result=result))
+
+    # Use Tabulate to print results
+    print_results(results)
+
+
+if __name__ == "__main__":
+    main()
diff --git a/test/prototype/mx_formats/test_kernels.py b/test/prototype/mx_formats/test_kernels.py
@@ -37,12 +37,13 @@
     pack_uint6,
     triton_f6_e2m3_to_bf16,
     triton_f6_e3m2_to_bf16,
+    triton_mxfp8_dequant_dim0,
     triton_to_mxfp8_dim0,
     triton_to_mxfp8_dim1,
     triton_to_mxfp8_dim1_reference,
     unpack_uint4,
 )
-from torchao.prototype.mx_formats.mx_tensor import ScaleCalculationMode, to_mx
+from torchao.prototype.mx_formats.mx_tensor import ScaleCalculationMode, to_dtype, to_mx
 from torchao.prototype.mx_formats.utils import to_blocked
 from torchao.utils import (
     is_sm_at_least_89,
@@ -513,6 +514,28 @@ def test_triton_mxfp8_dim0_zeros():
     torch.testing.assert_close(x_s_t, x_s_ref, rtol=0, atol=0)
 
 
+@pytest.mark.skipif(not has_triton(), reason="unsupported without triton")
+@pytest.mark.skipif(
+    not is_sm_at_least_100(),
+    reason="mxfp8 requires CUDA capability 10.0 or greater",
+)
+@pytest.mark.parametrize("M", (256, 2048, 131072))
+@pytest.mark.parametrize("K", (256, 5120, 7168))
+def test_triton_mxfp8_dequant_dim0(M, K):
+    x = torch.zeros(M, K, dtype=torch.bfloat16, device="cuda")
+    block_size = 32
+    x_data, x_scales = triton_to_mxfp8_dim0_reference(x, block_size=32)
+    hp_ref = to_dtype(
+        x_data,
+        x_scales,
+        torch.float8_e4m3fn,
+        block_size,
+        torch.bfloat16,
+    )
+    hp_t = triton_mxfp8_dequant_dim0(x_data, x_scales, torch.bfloat16, block_size)
+    torch.testing.assert_close(hp_t, hp_ref, rtol=0, atol=0)
+
+
 @pytest.mark.skipif(not torch.cuda.is_available(), reason="CUDA not available")
 @pytest.mark.parametrize(
     "shape",
diff --git a/torchao/prototype/mx_formats/kernels.py b/torchao/prototype/mx_formats/kernels.py
@@ -880,17 +880,19 @@ def _get_mxfp8_quant_autotune_configs():
         # sweep over a small set of shapes, it's likely that this
         # can be improved in the future.
         results = []
-        for ROW_TILE_SIZE in (64, 128):
-            for COL_TILE_SIZE in (64, 128):
-                for num_warps in (1, 2, 4):
-                    config = triton.Config(
-                        {
-                            "ROW_TILE_SIZE": ROW_TILE_SIZE,
-                            "COL_TILE_SIZE": COL_TILE_SIZE,
-                        },
-                        num_warps=num_warps,
-                    )
-                    results.append(config)
+        for ROW_TILE_SIZE in (128, 256, 512):
+            for COL_TILE_SIZE in (128, 256, 512):
+                for num_warps in (4, 8):
+                    for num_stages in (2, 3):
+                        config = triton.Config(
+                            {
+                                "ROW_TILE_SIZE": ROW_TILE_SIZE,
+                                "COL_TILE_SIZE": COL_TILE_SIZE,
+                            },
+                            num_warps=num_warps,
+                            num_stages=num_stages,
+                        )
+                        results.append(config)
         return results
 
     @triton.autotune(
@@ -1277,6 +1279,105 @@ def triton_to_mxfp8_dim1_reference(
             scale_e8m0_dim1,
         )
 
+    def triton_mxfp8_dequant_dim0(
+        e4m3_data: torch.Tensor,
+        e8m0_scales: torch.Tensor,
+        out_dtype: torch.dtype,
+        scale_block_size: int = 32,
+    ) -> None:
+        assert scale_block_size == 32, "scale_block_size must be 32 for now"
+        assert out_dtype in (torch.bfloat16, torch.float32), (
+            "out_dtype must be bf16 or fp32"
+        )
+
+        # Input shape must be 2D.
+        orig_shape = e4m3_data.shape
+        e4m3_data = e4m3_data.reshape(-1, orig_shape[-1])
+        out_buffer = torch.empty_like(e4m3_data, dtype=out_dtype)
+        out_dtype_tl = tl.bfloat16 if out_dtype == torch.bfloat16 else tl.float32
+
+        grid = lambda META: (
+            triton.cdiv(e4m3_data.shape[0], META["ROW_TILE_SIZE"]),
+            triton.cdiv(e4m3_data.shape[1], META["COL_TILE_SIZE"]),
+        )
+        _dequant_mxfp8_kernel[grid](
+            e4m3_data,
+            e8m0_scales.to(torch.uint8),
+            out_buffer,
+            e4m3_data.size(0),
+            e4m3_data.size(1),
+            e8m0_scales.size(0),
+            e8m0_scales.size(1),
+            out_dtype=out_dtype_tl,
+            SCALE_BLOCK_SIZE=scale_block_size,
+        )
+        return out_buffer.reshape(orig_shape)
+
+    @triton.autotune(
+        configs=_get_mxfp8_quant_autotune_configs(),
+        key=["input_num_cols", "SCALE_BLOCK_SIZE"],
+    )
+    @triton.jit
+    def _dequant_mxfp8_kernel(
+        e4m3_data,
+        e8m0_scales,
+        out_buffer,
+        input_num_rows,
+        input_num_cols,
+        scale_num_rows,
+        scale_num_cols,
+        out_dtype: tl.constexpr,
+        SCALE_BLOCK_SIZE: tl.constexpr,
+        ROW_TILE_SIZE: tl.constexpr,
+        COL_TILE_SIZE: tl.constexpr,
+    ):
+        pid_row = tl.program_id(0)
+        pid_col = tl.program_id(1)
+        SCALE_BLOCKS_PER_COL_TILE: tl.constexpr = COL_TILE_SIZE // SCALE_BLOCK_SIZE
+
+        # Load block of e4m3 data
+        row_offs = pid_row * ROW_TILE_SIZE + tl.arange(0, ROW_TILE_SIZE)
+        col_offs = pid_col * COL_TILE_SIZE + tl.arange(0, COL_TILE_SIZE)
+        block_offs = row_offs[:, None] * input_num_cols + col_offs[None, :]
+        mask = (row_offs[:, None] < input_num_rows) & (
+            col_offs[None, :] < input_num_cols
+        )
+        e4m3_data_block = tl.load(e4m3_data + block_offs, mask=mask)
+
+        # Load block of e8m0 scales
+        scale_col_offs = pid_col * SCALE_BLOCKS_PER_COL_TILE + tl.arange(
+            0, SCALE_BLOCKS_PER_COL_TILE
+        )
+        scale_block_offs = row_offs[:, None] * scale_num_cols + scale_col_offs[None, :]
+        scale_mask = (row_offs[:, None] < scale_num_rows) & (
+            scale_col_offs[None, :] < scale_num_cols
+        )
+        e8m0_scale_block = tl.load(e8m0_scales + scale_block_offs, mask=scale_mask)
+
+        # Dequantize and return output
+        e4m3_data_block_r = e4m3_data_block.reshape(
+            ROW_TILE_SIZE * SCALE_BLOCKS_PER_COL_TILE, SCALE_BLOCK_SIZE
+        )
+        e8m0_scale_block_r = e8m0_scale_block.reshape(
+            ROW_TILE_SIZE * SCALE_BLOCKS_PER_COL_TILE, 1
+        )
+        fp32_scale = _e8m0_to_fp32(e8m0_scale_block_r)
+        data_hp = e4m3_data_block_r.to(tl.float32) * fp32_scale
+
+        # Write to output buffer
+        out_buffer_block = data_hp.to(out_dtype)
+        out_buffer_block = out_buffer_block.reshape(ROW_TILE_SIZE, COL_TILE_SIZE)
+        tl.store(out_buffer + block_offs, out_buffer_block, mask=mask)
+
+    @triton.jit
+    def _e8m0_to_fp32(scale_e8m0):
+        e8m0_exponent_bias = 127
+        e8m0_nan_val = 255
+        s_offset = scale_e8m0.to(tl.int16) - e8m0_exponent_bias
+        s_fp = tl.exp2(s_offset.to(tl.float32))
+        s_fp = tl.where(scale_e8m0 != e8m0_nan_val, s_fp, float("nan"))
+        return s_fp.to(tl.float32)
+
     @triton.jit
     def triton_scale_swizzle(
         scale_ptr,
@@ -1641,6 +1742,14 @@ def triton_quantize_nvfp4(
     ) -> Tuple[torch.Tensor, torch.Tensor]:
         raise AssertionError("needs torch version 2.8+ and triton")
 
+    def triton_mxfp8_dequant_dim0(
+        e4m3_data: torch.Tensor,
+        e8m0_scales: torch.Tensor,
+        out_dtype: torch.dtype,
+        inner_block_size=32,
+    ) -> torch.Tensor:
+        raise AssertionError("needs torch version 2.8+ and triton")
+
 
 mxfp8_cuda_extension_available = False
 if is_sm_at_least_100():
