Support HuggingFace kernels package for native diffusion attention backends (#4926)

Signed-off-by: samithuang <285365963@qq.com>
Signed-off-by: Samit <285365963@qq.com>

tests/diffusion/attention/test_kernels_hub.py

@@ -0,0 +1,104 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+
+import sys
+import types
+
+import pytest
+import torch
+
+from tests.helpers.mark import hardware_test
+from vllm_omni.diffusion.attention.backends.abstract import AttentionMetadata
+from vllm_omni.diffusion.attention.backends.registry import DiffusionAttentionBackendEnum
+from vllm_omni.diffusion.attention.backends.sdpa import SDPAImpl
+from vllm_omni.platforms import current_omni_platform
+
+
+@pytest.mark.core_model
+@pytest.mark.cpu
+def test_kernels_hub_platform_fallback(monkeypatch: pytest.MonkeyPatch):
+    """Test that when kernels package is not available, the platform fallback logic
+
+    routes to local FLASH_ATTN.
+    """
+    from vllm_omni.platforms.cuda.platform import CudaOmniPlatform
+
+    # Temporarily hide/remove kernels module if present
+    monkeypatch.setitem(sys.modules, "kernels", None)
+
+    # Use monkeypatch to mock CudaOmniPlatform capability and package checker to allow FLASH_ATTN
+    from vllm.platforms.interface import DeviceCapability
+
+    from vllm_omni.diffusion.envs import PACKAGES_CHECKER
+
+    monkeypatch.setattr(
+        CudaOmniPlatform,
+        "get_device_capability",
+        classmethod(lambda cls, device_id=0: DeviceCapability(8, 0)),
+    )
+    monkeypatch.setattr(PACKAGES_CHECKER, "get_packages_info", lambda: {"has_flash_attn": True})
+
+    # Test FLASH_ATTN_HUB falls back to FLASH_ATTN when kernels is unavailable
+    backend_path = CudaOmniPlatform.get_diffusion_attn_backend_cls("FLASH_ATTN_HUB", head_size=64)
+    assert backend_path == DiffusionAttentionBackendEnum.FLASH_ATTN.get_path()
+
+    # Test FLASH_ATTN_3_HUB falls back to FLASH_ATTN when kernels is unavailable
+    backend_path = CudaOmniPlatform.get_diffusion_attn_backend_cls("FLASH_ATTN_3_HUB", head_size=64)
+    assert backend_path == DiffusionAttentionBackendEnum.FLASH_ATTN.get_path()
+
+    # Test FLASH_ATTN_3_HUB falls back to FLASH_ATTN_HUB on pre-Hopper GPUs
+    kernels_module = types.ModuleType("kernels")
+    monkeypatch.setitem(sys.modules, "kernels", kernels_module)
+    backend_path = CudaOmniPlatform.get_diffusion_attn_backend_cls("FLASH_ATTN_3_HUB", head_size=64)
+    assert backend_path == DiffusionAttentionBackendEnum.FLASH_ATTN_HUB.get_path()
+
+
+@pytest.mark.core_model
+@hardware_test(res={"cuda": "L4"}, num_cards=1)
+def test_kernels_hub_execution():
+    """Verify basic forward of flash_attn_hub and flash_attn_3_hub, comparing with SDPA reference."""
+    device = torch.device(current_omni_platform.device_type)
+    dtype = torch.bfloat16
+
+    num_heads = 8
+    head_dim = 64
+    seq_len = 32
+    batch_size = 1
+
+    torch.manual_seed(42)
+    q = torch.randn(batch_size, seq_len, num_heads, head_dim, device=device, dtype=dtype)
+    k = q.clone()
+    v = q.clone()
+
+    # 1. Test PyTorch SDPA reference
+    sdpa_impl = SDPAImpl(num_heads=num_heads, head_size=head_dim, softmax_scale=1.0 / (head_dim**0.5), causal=False)
+    attn_metadata_sdpa = AttentionMetadata(attn_mask=None)
+    output_ref = sdpa_impl.forward(q.clone(), k.clone(), v.clone(), attn_metadata_sdpa)
+
+    # 2. Test FlashAttentionHubBackend (FlashAttention 2)
+    from vllm_omni.diffusion.attention.backends.flash_attn_hub import FlashAttentionHubImpl
+
+    fa_hub_impl = FlashAttentionHubImpl(
+        num_heads=num_heads, head_size=head_dim, softmax_scale=1.0 / (head_dim**0.5), causal=False
+    )
+    output_fa_hub = fa_hub_impl.forward(q.clone(), k.clone(), v.clone(), attn_metadata_sdpa)
+    assert output_fa_hub.shape == q.shape
+    assert not torch.isnan(output_fa_hub).any()
+    max_diff = torch.max(torch.abs(output_ref - output_fa_hub)).item()
+    assert max_diff < 1e-2, f"FlashAttentionHub output differs too much from SDPA reference: {max_diff}"
+
+    # 3. Test FlashAttention3HubBackend (FlashAttention 3, Hopper+ only)
+    major, _minor = torch.cuda.get_device_capability()
+    if major < 9:
+        pytest.skip("FLASH_ATTN_3_HUB execution requires Hopper-class GPU (compute capability >= 9.0)")
+
+    from vllm_omni.diffusion.attention.backends.flash_attn_hub import FlashAttention3HubImpl
+
+    fa3_hub_impl = FlashAttention3HubImpl(
+        num_heads=num_heads, head_size=head_dim, softmax_scale=1.0 / (head_dim**0.5), causal=False
+    )
+    output_fa3_hub = fa3_hub_impl.forward(q.clone(), k.clone(), v.clone(), attn_metadata_sdpa)
+    assert output_fa3_hub.shape == q.shape
+    assert not torch.isnan(output_fa3_hub).any()
+    max_diff = torch.max(torch.abs(output_ref - output_fa3_hub)).item()
+    assert max_diff < 1e-2, f"FlashAttention3Hub output differs too much from SDPA reference: {max_diff}"