Tensorflow on shared GPUs: how to automatically select the one that is unused - tensorflow

Question

I have access through ssh to a cluster of n GPUs. Tensorflow automatically gave them names gpu:0,...,gpu:(n-1).
Others have access too and sometimes they take random gpus.
I did not place any tf.device() explicitely because that is cumbersome and even if I selected gpu number j and that someone is already on gpu number j that would be problematic.
I would like to go throuh the gpus usage and find the first that is unused and use only this one.
I guess someone could parse the output of nvidia-smi with bash and get a variable i and feed that variable i to the tensorflow script as the number of the gpu to use.
I have never seen any example of this. I imagine it is a pretty common problem. What would be the simplest way to do that ? Is a pure tensorflow one available ?

Answer 1

I'm not aware of pure-TensorFlow solution. The problem is that existing place for TensorFlow configurations is a Session config. However, for GPU memory, a GPU memory pool is shared for all TensorFlow sessions within a process, so Session config would be the wrong place to add it, and there's no mechanism for process-global config (but there should be, to also be able to configure process-global Eigen threadpool). So you need to do on on a process level by using CUDA_VISIBLE_DEVICES environment variable.
Something like this:
import subprocess, re
# Nvidia-smi GPU memory parsing.
# Tested on nvidia-smi 370.23
def run_command(cmd):
"""Run command, return output as string."""
output = subprocess.Popen(cmd, stdout=subprocess.PIPE, shell=True).communicate()[0]
return output.decode("ascii")
def list_available_gpus():
"""Returns list of available GPU ids."""
output = run_command("nvidia-smi -L")
# lines of the form GPU 0: TITAN X
gpu_regex = re.compile(r"GPU (?P<gpu_id>\d+):")
result = []
for line in output.strip().split("\n"):
m = gpu_regex.match(line)
assert m, "Couldnt parse "+line
result.append(int(m.group("gpu_id")))
return result
def gpu_memory_map():
"""Returns map of GPU id to memory allocated on that GPU."""
output = run_command("nvidia-smi")
gpu_output = output[output.find("GPU Memory"):]
# lines of the form
# | 0 8734 C python 11705MiB |
memory_regex = re.compile(r"[|]\s+?(?P<gpu_id>\d+)\D+?(?P<pid>\d+).+[ ](?P<gpu_memory>\d+)MiB")
rows = gpu_output.split("\n")
result = {gpu_id: 0 for gpu_id in list_available_gpus()}
for row in gpu_output.split("\n"):
m = memory_regex.search(row)
if not m:
continue
gpu_id = int(m.group("gpu_id"))
gpu_memory = int(m.group("gpu_memory"))
result[gpu_id] += gpu_memory
return result
def pick_gpu_lowest_memory():
"""Returns GPU with the least allocated memory"""
memory_gpu_map = [(memory, gpu_id) for (gpu_id, memory) in gpu_memory_map().items()]
best_memory, best_gpu = sorted(memory_gpu_map)[0]
return best_gpu
You can then put it in utils.py and set GPU in your TensorFlow script before first tensorflow import. IE
import utils
import os
os.environ["CUDA_VISIBLE_DEVICES"] = str(utils.pick_gpu_lowest_memory())
import tensorflow

Answer 2

An implementation along the lines of Yaroslav Bulatov's solution is available on https://github.com/bamos/setGPU.