The Operator Vectorization Library, or OVL, is a python library for defining high performance custom operators for the TensorFlow platform. OVL enables TensorFlow users to easily write, test, and use custom operators in pure python without sacrificing performance. This circumvents the productivity bottleneck of implementing, building, and linking custom C++ and CUDA operators or propagating them through the Eigen code base.
Key features include:
- A single python implementation is used to generate both C++ and CUDA operators and transparently link them into the TensorFlow run time, cutting out the overhead of implementing, testing, and maintaining operators for multiple hardware architectures.
- An optimizer which can fuse an unbounded number of qualifying OVL operators into a single function call, mitigating performance bottlenecks related to global memory bandwidth limits and operator launch overhead.
- A python testing framework so that users can directly test and profile their operators, on both the CPU and GPU, against a python-native reference like numpy.
- Straightforward gradient definition, enabling OVL operators to be fully integrated in the middle of a broader neural network or other gradient-dependent TensorFlow graph.
- A standard library of OVL operators which can be optimized in conjunction with user defined ops and used for defining operator gradients
OVL operators are not intended to replace performance-tuned core API operators (e.g. CUDNN library calls). OVL operators are not intended to replace all custom operator use cases -- sometimes there is no substitute to an expert writing/tuning a C++/CUDA operator directly. For everything else, the mission of OVL is to offer a significant productivity gain for implementing custom ops without introducing performance bottlenecks.
Users write OVL ops by implementing a vectorized function which statelessly maps input tensors into output tensors. The key abstraction of the OVL programming model is the parallel for, aka map. The user defines an abstractly shaped workgroup and a worker function which is applied over the indices of that workgroup. Each worker knows its indices within the workgroup and can read (write) from (to) any point in the input (output) tensors.
An example code snippet of a slightly more than trivial OVL operator for shifting the values of a 1D tensor by 1 element:
.. testcode:: import tensorflow as tf import opveclib as ovl @ovl.operator() def shift_cyclic(input_tensor): # make sure input is 1D assert input_tensor.rank == 1 # define the output tensor output_tensor = ovl.output_like(input_tensor) # define the workgroup shape and get workgroup position reference wg_position = ovl.position_in(input_tensor.shape) # read input element at current workgroup position input_element = input_tensor[wg_position] # define the output position to be 1 greater than the input/workgroup position output_position = (wg_position + 1) % input_tensor.size # set the output element output_tensor[output_position] = input_element return output_tensor a = tf.constant([0, 1, 2, 3, 4], dtype=tf.float32) b = ovl.as_tensorflow(shift_cyclic(a)) sess = tf.Session() print(sess.run([b]))
.. testoutput:: [array([ 4., 0., 1., 2., 3.], dtype=float32)]
Full documentation is available here.
White paper is available here.
OVL is currently tested and supported under Ubuntu 14.04, python 2.7 and 3.4, and is compatible with both the CPU and GPU versions of TensorFlow. OVL requires a c++ compiler to be available on the system and is currently only tested with g++. OVL has been tested with the following nvidia GPUs:
GeForce GTX TITAN GeForce GTX TITAN Black
OVL requires TensorFlow 0.11.0 and works with both the CPU and GPU versions. Installation instructions are available here. Users are recommended follow the TensorFlow installation guide and its testing/troubleshooting recommendations before using OVL.
OVL detects which version of TensorFlow, CPU or GPU, is installed at runtime. If the GPU version is installed, both CPU and GPU versions of the operators will be generated. To do so, OVL requires access to CUDA which should have been installed already during the GPU-enabled TensorFlow installation process. OVL assumes the CUDA install path to be '/usr/local/cuda' - if this is incorrect the user must set the correct path in the 'CUDA_HOME' environment variable.
Install c++ compiler and nose2
OVL requires a c++ compiler to be available in order to generate operators that run on the CPU. The default c++ compiler is g++, but this can be overridden by setting a custom compiler path in the OPVECLIB_CXX environment variable. OVL uses nose2 to run tests, so it is recommended to install as well to test the installation.
sudo apt-get install python-nose2 g++
Install the latest release of OVL:
sudo pip install --upgrade opveclib
If you see an error message during the install like
libcudart.so.8.0: cannot open shared object file: No such file or directory, this likely means that the CUDA
library path is not exposed to the sudo environment. To solve this issue you
may explicitly pass an
LD_LIBRARY_PATH to sudo to install the package:
sudo LD_LIBRARY_PATH=/usr/local/cuda/lib64 pip install --upgrade opveclib
Test your installation
To test that your installation is correct, run the OVL build acceptance test:
nose2 -F opveclib.test -A '!regression' --verbose
The GPU version of TensorFlow requires CUDA to be installed on your system. Depending on how CUDA is installed, you may need to explicitly set the CUDA_HOME environment variable, typically:
If you see an error like:
ImportError: libcudart.so.8.0: cannot open shared object file: No such file or directory
You may also need to make sure the CUDA libraries are on your library path, typically:
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