Is it impossible to use multi-GPUs ?

[youngwanLEE]

I tried to use multi-GPUs by inserting num_clones=4 argument.

but, below error occurred.

InvalidArgumentError (see above for traceback): Cannot assign a device to node 'clone_3/ssd_losses/block_5/cross_entropy_neg/SparseSoftmaxCrossEntropyWithLogits/Gather': Could not satisfy explicit device specification '/device:GPU:3' because no supported kernel for GPU devices is available.
         [[Node: clone_3/ssd_losses/block_5/cross_entropy_neg/SparseSoftmaxCrossEntropyWithLogits/Gather = Gather[Tindices=DT_INT32, Tparams=DT_INT32, validate_indices=true, _device="/device:GPU:3"](clone_3/ssd_losses/block_5/cross_entropy_neg/SparseSoftmaxCrossEntropyWithLogits/Shape_1, clone_3/ssd_losses/block_5/cross_entropy_neg/SparseSoftmaxCrossEntropyWithLogits/sub)]]

Could you advice for using multi-GPUs ?