[gpt-oss] Add gpt-oss bf16 support

vllm/attention/utils/fa_utils.py

@@ -0,0 +1,55 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+from typing import Optional
+
+from vllm import envs
+from vllm.logger import init_logger
+
+logger = init_logger(__name__)
+
+
+def get_flash_attn_version(requires_alibi: bool = False) -> Optional[int]:
+    # import here to avoid circular dependencies
+    from vllm.platforms import current_platform
+    try:
+        from vllm.vllm_flash_attn.flash_attn_interface import (
+            fa_version_unsupported_reason, is_fa_version_supported)
+        device_capability = current_platform.get_device_capability()
+
+        assert device_capability is not None
+
+        # 1. default version depending on platform
+        fa_version = 3 if (device_capability.major == 9
+                           and is_fa_version_supported(3)) else 2
+
+        # 2. override if passed by environment
+        if envs.VLLM_FLASH_ATTN_VERSION is not None:
+            assert envs.VLLM_FLASH_ATTN_VERSION in [2, 3]
+            fa_version = envs.VLLM_FLASH_ATTN_VERSION
+
+        # 3. fallback for unsupported combinations
+        if device_capability.major == 10 and fa_version == 3:
+            logger.warning_once(
+                "Cannot use FA version 3 on Blackwell platform "
+                "defaulting to FA version 2.")
+            fa_version = 2
+
+        if requires_alibi and fa_version == 3:
+            logger.warning_once("Cannot use FA version 3 with ALiBi, "
+                                "defaulting to FA version 2.")
+            fa_version = 2
+
+        if not is_fa_version_supported(fa_version):
+            logger.error("Cannot use FA version %d is not supported due to %s",
+                         fa_version, fa_version_unsupported_reason(fa_version))
+
+        assert is_fa_version_supported(fa_version)
+        return fa_version
+    except (ImportError, AssertionError):
+        return None
+
+
+def flash_attn_supports_fp8() -> bool:
+    from vllm.platforms import current_platform
+    return get_flash_attn_version() == 3 and \
+        current_platform.get_device_capability().major == 9