feat(magi2): add fused mHC post-processing (#7261)

Signed-off-by: Xiaodong Ye <xiaodong.ye@mthreads.com>
Co-authored-by: Hongsheng Liu <liuhongsheng4@huawei.com>

benchmarks/kernels/benchmark_magi2_mhc.py

@@ -0,0 +1,141 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM-Omni project
+"""Compare native and fused MAGI-2 mHC post-processing on CUDA or MUSA.
+
+Run from the checkout root with PyTorch and the selected backend dependencies.
+torchada is loaded automatically only on MUSA::
+
+    python -m benchmarks.kernels.benchmark_magi2_mhc \
+        --tokens 1 4 16 64 129 4096 --hidden-size 3072 --num-tests 30
+
+The released config supplies hidden=3072, four streams and 20 Sinkhorn steps.
+Token counts are synthetic; supply per-rank sizes from the target trace when
+comparing production shapes. FP32 post/residual logits are strided views of the
+same [tokens, 24] projection, as in MHCHandler.compute_logits. Mix inputs use
+the selected dtype. Both mix implementations consume identical coefficients.
+
+The three comparisons cover coefficient preparation, stream mixing, and their
+combined pipeline (including intermediate allocations, excluding projection,
+normalization and apply_pre). This is an eager operator diagnostic, without
+compile or graph capture. It does not measure full model performance.
+No CUDA/MUSA device (or no PyTorch) produces a JSON skip record and exit status zero.
+"""
+
+import argparse
+import math
+from functools import partial
+from typing import Any
+
+from benchmarks.kernels._magi2_gpu_bench import (
+    add_arguments,
+    check_pair,
+    emit,
+    load_musa,
+    measure_pair,
+    report_environment,
+)
+
+
+def benchmark_shape(torch: Any, mhc: Any, args: argparse.Namespace, tokens: int) -> None:
+    dtype = getattr(torch, args.dtype)
+    device = torch.device("cuda")
+    packed = torch.randn(tokens, 24, device=device, dtype=torch.float32)
+    # Preserve the token stride of the model's shared projection allocation.
+    post_inputs = (
+        packed[:, 4:8],
+        packed[:, 8:].view(tokens, 4, 4),
+        torch.tensor([0.8], device=device),
+        torch.randn(4, device=device),
+        torch.tensor([1.1], device=device),
+        torch.randn(4, 4, device=device),
+    )
+    streams = torch.randn(tokens, 4, args.hidden_size, device=device, dtype=dtype)
+    branch = torch.randn(tokens, args.hidden_size, device=device, dtype=dtype)
+    post_op, mix_op = mhc.MHCPostResidual(), mhc.MHCMix()
+    scale = 1 / math.sqrt(4 * args.hidden_size)
+    kwargs = dict(scale=scale, iterations=args.sinkhorn_iterations, epsilon=1e-12, out_dtype=dtype)
+    prepare_reference = partial(post_op.forward_native, *post_inputs, **kwargs)
+    prepare_fused = partial(post_op, *post_inputs, **kwargs)
+    coefficients = prepare_reference()
+    mix_reference = partial(mix_op.forward_native, streams, branch, *coefficients)
+    mix_fused = partial(mix_op, streams, branch, *coefficients)
+    post_kernel, mix_kernel = "_mhc_post_residual_kernel", "_mhc_mix_kernel"
+    cases = {
+        "post_residual": (prepare_reference, prepare_fused, (post_kernel,)),
+        "mix": (mix_reference, mix_fused, (mix_kernel,)),
+        "pipeline": (
+            lambda: mix_op.forward_native(streams, branch, *prepare_reference()),
+            lambda: mix_op(streams, branch, *prepare_fused()),
+            (post_kernel, mix_kernel),
+        ),
+    }
+    rtol = {torch.bfloat16: 1.6e-2, torch.float16: 2e-3, torch.float32: 1e-5}[dtype]
+    for name, (reference, fused, kernels) in cases.items():
+        if args.op != "all" and args.op != name:
+            continue
+        # BF16 MUSA custom ops can quantize values near zero to the adjacent
+        # representable value; retain the strict relative gate while allowing
+        # one BF16 ulp in the absolute comparison.
+        atol = (
+            (1e-2 if dtype == torch.bfloat16 else 1e-6)
+            if name == "post_residual"
+            else (1e-2 if dtype == torch.bfloat16 else 1e-5)
+        )
+        parity = check_pair(torch, reference, fused, mhc, kernels, rtol=rtol, atol=atol)
+        timing = measure_pair(torch, reference, fused, args)
+        # Logical minimum traffic: input reads plus output writes. Native
+        # intermediates and repeat parameter loads can add actual DRAM traffic.
+        element_bytes = streams.element_size()
+        prepare_bytes = tokens * 20 * (4 + element_bytes) + 22 * 4
+        mix_bytes = tokens * (9 * args.hidden_size + 20) * element_bytes
+        minimum_bytes = {"post_residual": prepare_bytes, "mix": mix_bytes, "pipeline": prepare_bytes + mix_bytes}[name]
+        # Sigmoid/exp costs and max reductions are not represented as FLOPs.
+        prepare_flops = tokens * (72 + 64 * args.sinkhorn_iterations)
+        mix_flops = tokens * args.hidden_size * 36
+        scalar_flops = {"post_residual": prepare_flops, "mix": mix_flops, "pipeline": prepare_flops + mix_flops}[name]
+        emit(
+            status="pass",
+            op=name,
+            tokens=tokens,
+            hidden_size=args.hidden_size,
+            num_streams=4,
+            dtype=args.dtype,
+            logits_dtype="float32",
+            packed_shape=list(packed.shape),
+            post_stride=list(post_inputs[0].stride()),
+            residual_stride=list(post_inputs[1].stride()),
+            scale=scale,
+            sinkhorn_iterations=args.sinkhorn_iterations,
+            epsilon=1e-12,
+            minimum_io_bytes=minimum_bytes,
+            scalar_flops_excluding_exp_and_max=scalar_flops,
+            effective_fused_gbps=minimum_bytes / timing["fused"]["p50_us"] / 1000,
+            **parity,
+            **timing,
+        )
+
+
+def main() -> None:
+    parser = argparse.ArgumentParser(description=__doc__, formatter_class=argparse.RawDescriptionHelpFormatter)
+    add_arguments(parser)
+    parser.add_argument("--hidden-size", type=int, default=3072)
+    parser.add_argument("--sinkhorn-iterations", type=int, default=20)
+    parser.add_argument("--op", choices=["all", "post_residual", "mix", "pipeline"], default="all")
+    args = parser.parse_args()
+    if args.hidden_size <= 0 or not 0 <= args.sinkhorn_iterations <= 64:
+        parser.error("hidden-size must be positive; sinkhorn-iterations must be in [0, 64]")
+    torch = load_musa(args, parser)
+    if torch is None:
+        return
+    cuda = getattr(torch, "cuda")
+    from vllm_omni.diffusion.layers import mhc
+
+    report_environment(torch, args, mhc)
+    with torch.inference_mode():
+        for tokens in args.tokens:
+            benchmark_shape(torch, mhc, args, tokens)
+            cuda.empty_cache()
+
+
+if __name__ == "__main__":
+    main()