Warning when I run tensorflow-gpu. Is it using the GPU? - tensorflow

Question

When I run this command:
sess = tf.Session(config=tf.ConfigProto(log_device_placement=True))
I get this log:
2017-06-16 11:29:42.305931: W tensorflow/core/platform/cpu_feature_guard.cc:45] The TensorFlow library wasn't compiled to use SSE4.1 instructions, but these are available on your machine and could speed up CPU computations.
2017-06-16 11:29:42.305950: W tensorflow/core/platform/cpu_feature_guard.cc:45] The TensorFlow library wasn't compiled to use SSE4.2 instructions, but these are available on your machine and could speed up CPU computations.
2017-06-16 11:29:42.305963: W tensorflow/core/platform/cpu_feature_guard.cc:45] The TensorFlow library wasn't compiled to use AVX instructions, but these are available on your machine and could speed up CPU computations.
2017-06-16 11:29:42.305975: W tensorflow/core/platform/cpu_feature_guard.cc:45] The TensorFlow library wasn't compiled to use AVX2 instructions, but these are available on your machine and could speed up CPU computations.
2017-06-16 11:29:42.305986: W tensorflow/core/platform/cpu_feature_guard.cc:45] The TensorFlow library wasn't compiled to use FMA instructions, but these are available on your machine and could speed up CPU computations.
2017-06-16 11:29:42.406689: I tensorflow/stream_executor/cuda/cuda_gpu_executor.cc:901] successful NUMA node read from SysFS had negative value (-1), but there must be at least one NUMA node, so returning NUMA node zero
2017-06-16 11:29:42.406961: I tensorflow/core/common_runtime/gpu/gpu_device.cc:887] Found device 0 with properties:
name: GeForce GTX 1070
major: 6 minor: 1 memoryClockRate (GHz) 1.7715
pciBusID 0000:01:00.0
Total memory: 7.92GiB
Free memory: 248.75MiB
2017-06-16 11:29:42.406991: I tensorflow/core/common_runtime/gpu/gpu_device.cc:908] DMA: 0
2017-06-16 11:29:42.407010: I tensorflow/core/common_runtime/gpu/gpu_device.cc:918] 0: Y
2017-06-16 11:29:42.407021: I tensorflow/core/common_runtime/gpu/gpu_device.cc:977] Creating TensorFlow device (/gpu:0) -> (device: 0, name: GeForce GTX 1070, pci bus id: 0000:01:00.0)
Device mapping:
/job:localhost/replica:0/task:0/gpu:0 -> device: 0, name: GeForce GTX 1070, pci bus id: 0000:01:00.0
2017-06-16 11:29:42.408087: I tensorflow/core/common_runtime/direct_session.cc:257] Device mapping:
/job:localhost/replica:0/task:0/gpu:0 -> device: 0, name: GeForce GTX 1070, pci bus id: 0000:01:00.0
Does this assure me that tensorflow code will use GPU? I had a previous version of tensorflow and the message was clear that it used GPU. Now after I upgraded it, the messages are different and confusing.
I can see that it discovered my GPU, but is it using it for sure or still using the CPU? How can I check this from the code to make sure the device used is GPU?
I'm concerned because I have:
import keras
Using TensorFlow backend
It shows that keras is using a CPU version!

Answer 1

Use device scope as follow:
with tf.device('/gpu:0'):
a = tf.constant(0)
sess = tf.Session()
sess.run(a)
If it doesn't complain that it can't assign a device to node, you are using the GPU.
You can go one step further to analyse where each node is being allocated to through log_device_placement.