M. Massias M. Massias - 7 months ago 27
Python Question

Select GPU during execution in Theano

I am training neural nets with theano and lasagne on a 4 GPU machine. My

.theanorc
contains the following lines:

[global]
device = gpu0


So when in python I execute
import theano
, I get
Using gpu device 0: GRID K520


What if, after importing theano, I chose to use say gpu1? I'd like to do this dynamically, that is, without editing
.theanorc
is it possible? Or even to choose it at runtime?

Answer

I'm afraid it's not possible to change the execution device after Theano has been imported. From the documentation:

config.device

String value: either 'cpu', 'gpu', 'gpu0', 'gpu1', 'gpu2', or 'gpu3'

[...]

This flag’s value cannot be modified during the program execution.

Bonus: however, let's say you wanted to have two Python processes each running on a separate GPU (is that what you want?), then you could do something like:

import os
os.system("THEANO_FLAGS='device=gpu0' python myscript.py")
os.system("THEANO_FLAGS='device=gpu1' python myscript.py")

or hack into/extend Python's multiprocessing module (which works by spawning subprocesses) to ensure the flag is set before a child process is spawned.