Introduce VLLM_CUDART_SO_PATH to allow users specify the .so path (#12998)

Signed-off-by: Lu Fang <lufang@fb.com>

vllm/distributed/device_communicators/cuda_wrapper.py

@@ -5,12 +5,14 @@ convenient for use when we just need to call a few functions.
 """
 
 import ctypes
+import glob
 from dataclasses import dataclass
 from typing import Any, Dict, List, Optional
 
 # this line makes it possible to directly load `libcudart.so` using `ctypes`
 import torch  # noqa
 
+import vllm.envs as envs
 from vllm.logger import init_logger
 
 logger = init_logger(__name__)
@@ -60,6 +62,29 @@ def find_loaded_library(lib_name) -> Optional[str]:
     return path
 
 
+def get_cudart_lib_path_from_env() -> Optional[str]:
+    """
+    In some system, find_loaded_library() may not work. So we allow users to
+    specify the path through environment variable VLLM_CUDART_SO_PATH.
+    """
+    cudart_so_env = envs.VLLM_CUDART_SO_PATH
+    if cudart_so_env is not None:
+        cudart_paths = [
+            cudart_so_env,
+        ]
+        for path in cudart_paths:
+            file_paths = glob.glob(path)
+            if len(file_paths) > 0:
+                logger.info(
+                    "Found cudart library at %s through env var"
+                    "VLLM_CUDART_SO_PATH=%s",
+                    file_paths[0],
+                    cudart_so_env,
+                )
+                return file_paths[0]
+    return None
+
+
 class CudaRTLibrary:
     exported_functions = [
         # ​cudaError_t cudaSetDevice ( int  device )
@@ -105,8 +130,13 @@ class CudaRTLibrary:
     def __init__(self, so_file: Optional[str] = None):
         if so_file is None:
             so_file = find_loaded_library("libcudart")
+            if so_file is None:
+                so_file = get_cudart_lib_path_from_env()
             assert so_file is not None, \
-                "libcudart is not loaded in the current process"
+                (
+                    "libcudart is not loaded in the current process, "
+                    "try setting VLLM_CUDART_SO_PATH"
+                )
         if so_file not in CudaRTLibrary.path_to_library_cache:
             lib = ctypes.CDLL(so_file)
             CudaRTLibrary.path_to_library_cache[so_file] = lib

vllm/envs.py

@@ -87,6 +87,7 @@ if TYPE_CHECKING:
     VLLM_ENABLE_MOE_ALIGN_BLOCK_SIZE_TRITON: bool = False
     VLLM_RAY_PER_WORKER_GPUS: float = 1.0
     VLLM_RAY_BUNDLE_INDICES: str = ""
+    VLLM_CUDART_SO_PATH: Optional[str] = None
 
 
 def get_default_cache_root():
@@ -572,6 +573,11 @@ environment_variables: Dict[str, Callable[[], Any]] = {
     # models the alignment is already naturally aligned to 256 bytes.
     "VLLM_CUDA_MEM_ALIGN_KV_CACHE":
     lambda: bool(int(os.getenv("VLLM_CUDA_MEM_ALIGN_KV_CACHE", "1"))),
+
+    # In some system, find_loaded_library() may not work. So we allow users to
+    # specify the path through environment variable VLLM_CUDART_SO_PATH.
+    "VLLM_CUDART_SO_PATH":
+    lambda: os.getenv("VLLM_CUDART_SO_PATH", None),
 }
 
 # end-env-vars-definition