# Basic Multi GPU Computation in TensorFlow¶

Credits: Forked from TensorFlow-Examples by Aymeric Damien

## Setup¶

Refer to the setup instructions

This tutorial requires your machine to have 2 GPUs

• "/cpu:0": The CPU of your machine.
• "/gpu:0": The first GPU of your machine
• "/gpu:1": The second GPU of your machine
• For this example, we are using 2 GTX-980
In [2]:
import numpy as np
import tensorflow as tf
import datetime

In [3]:
#Processing Units logs
log_device_placement = True

#num of multiplications to perform
n = 10

In [ ]:
# Example: compute A^n + B^n on 2 GPUs

# Create random large matrix
A = np.random.rand(1e4, 1e4).astype('float32')
B = np.random.rand(1e4, 1e4).astype('float32')

# Creates a graph to store results
c1 = []
c2 = []

# Define matrix power
def matpow(M, n):
if n < 1: #Abstract cases where n < 1
return M
else:
return tf.matmul(M, matpow(M, n-1))

In [6]:
# Single GPU computing

with tf.device('/gpu:0'):
a = tf.constant(A)
b = tf.constant(B)
#compute A^n and B^n and store results in c1
c1.append(matpow(a, n))
c1.append(matpow(b, n))

with tf.device('/cpu:0'):
sum = tf.add_n(c1) #Addition of all elements in c1, i.e. A^n + B^n

t1_1 = datetime.datetime.now()
with tf.Session(config=tf.ConfigProto(log_device_placement=log_device_placement)) as sess:
# Runs the op.
sess.run(sum)
t2_1 = datetime.datetime.now()

In [7]:
# Multi GPU computing
# GPU:0 computes A^n
with tf.device('/gpu:0'):
#compute A^n and store result in c2
a = tf.constant(A)
c2.append(matpow(a, n))

#GPU:1 computes B^n
with tf.device('/gpu:1'):
#compute B^n and store result in c2
b = tf.constant(B)
c2.append(matpow(b, n))

with tf.device('/cpu:0'):
sum = tf.add_n(c2) #Addition of all elements in c2, i.e. A^n + B^n

t1_2 = datetime.datetime.now()
with tf.Session(config=tf.ConfigProto(log_device_placement=log_device_placement)) as sess:
# Runs the op.
sess.run(sum)
t2_2 = datetime.datetime.now()

In [8]:
print "Single GPU computation time: " + str(t2_1-t1_1)
print "Multi GPU computation time: " + str(t2_2-t1_2)

Single GPU computation time: 0:00:11.833497
Multi GPU computation time: 0:00:07.085913