[MaskRCNN] allow inference with MKL support (#1024)

examples/FasterRCNN/train.py

@@ -421,7 +421,9 @@ if __name__ == '__main__':
     DetectionDataset()  # initialize the config with information from our dataset
 
     if args.visualize or args.evaluate or args.predict:
-        assert tf.test.is_gpu_available()
+        if not tf.test.is_gpu_available():
+            from tensorflow.python.framework import test_util
+            assert test_util.IsMklEnabled(), "Inference requires either GPU support or MKL support!"
         assert args.load
         finalize_configs(is_training=False)
 

tensorpack/utils/gpu.py

@@ -44,7 +44,7 @@ def get_num_gpu():
         return ret
 
     env = os.environ.get('CUDA_VISIBLE_DEVICES', None)
-    if env is not None:
+    if env:
         return warn_return(len(env.split(',')), "Found non-empty CUDA_VISIBLE_DEVICES. ")
     output, code = subproc_call("nvidia-smi -L", timeout=5)
     if code == 0: