Can Keras with Tensorflow backend be forced to use CPU or GPU at will?

python machine-learning tensorflow keras
mikal94305 picture mikal94305 · Nov 19, 2016 · Viewed 124.7k times · Source

I have Keras installed with the Tensorflow backend and CUDA. I'd like to sometimes on demand force Keras to use CPU. Can this be done without say installing a separate CPU-only Tensorflow in a virtual environment? If so how? If the backend were Theano, the flags could be set, but I have not heard of Tensorflow flags accessible via Keras.

Answer

Martin Thoma picture Martin Thoma · Mar 12, 2017

If you want to force Keras to use CPU

Way 1

import os
os.environ["CUDA_DEVICE_ORDER"] = "PCI_BUS_ID"   # see issue #152
os.environ["CUDA_VISIBLE_DEVICES"] = ""

before Keras / Tensorflow is imported.

Way 2

Run your script as

$ CUDA_VISIBLE_DEVICES="" ./your_keras_code.py

See also

  1. https://github.com/keras-team/keras/issues/152
  2. https://github.com/fchollet/keras/issues/4613

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