add doc for env var
@@ -62,6 +62,14 @@ Here are the environment variables CuPy uses.
| | point compute. |
| | The default is 0 and TF32 is not used. |
+------------------------------------+----------------------------------------------------+
+| ``CUPY_CUDA_ARRAY_INTERFACE_SYNC`` | If set to 0, a stream synchronization will *not* |
+| | be performed when a device array crosses the |
+| | boundaries between CuPy and other external |
+| | libraries that implement the CUDA Array Interface. |
+| | Default is 1. For more detail, see the |
+| | `Synchronization`_ requirement in the CUDA Array |
+| | Interface documentation. |
++------------------------------------+----------------------------------------------------+
| ``NVCC`` | Define the compiler to use when compiling CUDA |
| | source. Note that most CuPy kernels are built with |
| | NVRTC; this environment is only effective for |
@@ -76,6 +84,8 @@ are set, g++-6 or later is required as the runtime host compiler. Please refer t
.. _CUDA Toolkit Documentation: https://docs.nvidia.com/cuda/cuda-c-programming-guide/index.html#env-vars
+.. _Synchronization: https://numba.readthedocs.io/en/latest/cuda/cuda_array_interface.html#synchronization
+
For installation
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