Using Tensorflow DALI plugin: simple example¶
Overview¶
Using our DALI data loading and augmentation pipeline with Tensorflow is pretty simple.
We can summarize the integration in 3 steps :
Defining a DALI Pipeline
Give the pipeline to
DALIIterator
opInstatiate the op in TensorFlow graph and use it
Defining the data loading pipeline¶
First we start by defining some parameters for DALI and Tensorflow.
We will use a subsample of Imagenet stored in a MXNet’s RecordIO for this tutorial. For details on how to use MXNetReader
as well as other readers please see other examples.
[1]:
base = "/data/imagenet/train-480-val-256-recordio/"
idx_files = [base + "val.idx"]
rec_files = [base + "val.rec"]
BATCH_SIZE = 32
DEVICES = 8
ITERATIONS = 32
BURNIN_STEPS = 16
In order to use DALI we need those 3 imports:
[2]:
from nvidia.dali.pipeline import Pipeline
import nvidia.dali.ops as ops
import nvidia.dali.types as types
Then we can define our pipeline by declaring RN50Pipeline
as as sublass of dali.pipeline.Pipeline
. We declare the operators the pipeline will need in the constructor. Then we define the graph in define_graph
.
This is the usual DALI Pipeline creation. For more information about DALI Pipeline, please take a look at Getting Started notebook.
Note again that we are using MXNetReader
that reads MXNet’s dataset format RecordIO. You can change it to other Reader ops to use any of the supported dataset format.
[3]:
class RN50Pipeline(Pipeline):
def __init__(self, batch_size, num_threads, device_id, num_gpus):
super(RN50Pipeline, self).__init__(batch_size,
num_threads,
device_id)
self.input = ops.MXNetReader(path = rec_files, index_path = idx_files,
shard_id = device_id, num_shards = num_gpus)
self.decode = ops.nvJPEGDecoder(device = "mixed", output_type = types.RGB)
self.resize = ops.Resize(device = "gpu",
image_type = types.RGB,
interp_type = types.INTERP_LINEAR)
self.cmn = ops.CropMirrorNormalize(device = "gpu",
output_dtype = types.FLOAT,
crop = (224, 224),
image_type = types.RGB,
mean = [128., 128., 128.],
std = [1., 1., 1.])
self.res_uniform = ops.Uniform(range = (256.,480.))
self.uniform = ops.Uniform(range = (0.0, 1.0))
self.cast = ops.Cast(device = "gpu",
dtype = types.INT32)
def define_graph(self):
inputs, labels = self.input(name="Reader")
images = self.decode(inputs)
images = self.resize(images, resize_shorter = self.res_uniform())
output = self.cmn(images, crop_pos_x = self.uniform(),
crop_pos_y = self.uniform())
output = self.cast(output)
return (output, labels.gpu())
Next, we instatiate the pipelines with the right parameters. We will create one pipeline per GPU, by specifying the right device_id
for each pipeline.
The difference is that instead of calling pipeline.build
and using it, we will pass the pipeline object to the TensorFlow operator.
[4]:
pipes = [RN50Pipeline(batch_size=BATCH_SIZE, num_threads=2, device_id = device_id, num_gpus = DEVICES) for device_id in range(DEVICES)]
Using DALI TensorFlow plugin¶
Let’s start by importing Tensorflow and the DALI Tensorflow plugin as dali_tf
.
[5]:
import tensorflow as tf
import nvidia.dali.plugin.tf as dali_tf
import time
We can now use nvidia.dali.plugin.tf.DALIIterator()
method to get the Tensorflow Op that will produce the tensors we will use in the Tensorflow graph.
For each DALI pipeline, we use daliop
that returns a Tensorflow tensor tuple that we will store in image, label
. Each one is using a different tf.device
.
[6]:
daliop = dali_tf.DALIIterator()
images = []
labels = []
for d in range(DEVICES):
with tf.device('/gpu:%i' % d):
image, label = daliop(pipeline = pipes[d],
shapes = [(BATCH_SIZE, 3, 224, 224), ()],
dtypes = [tf.int32, tf.float32])
images.append(image)
labels.append(label)
Using the tensors in a simple Tensorflow graph¶
We will use images
and labels
tensors list in our Tensorflow graph definition. Then run a very simple one op graph session that will output the batch of images and labels.
[7]:
from __future__ import print_function
gpu_options = tf.GPUOptions(per_process_gpu_memory_fraction=0.8)
config = tf.ConfigProto(gpu_options=gpu_options)
with tf.Session(config=config) as sess:
all_img_per_sec = []
total_batch_size = BATCH_SIZE * DEVICES
for i in range(ITERATIONS):
start_time = time.time()
# The actual run with our dali_tf tensors
res = sess.run([images, labels])
elapsed_time = time.time() - start_time
img_per_sec = total_batch_size / elapsed_time
if i > BURNIN_STEPS:
all_img_per_sec.append(img_per_sec)
print("\t%7.1f img/s" % img_per_sec)
print("Total average %7.1f img/s" % (sum(all_img_per_sec) / len(all_img_per_sec)))
4124.7 img/s
4500.0 img/s
4253.0 img/s
4668.1 img/s
4756.3 img/s
4067.6 img/s
3833.7 img/s
4380.5 img/s
4324.9 img/s
4270.6 img/s
4040.9 img/s
4500.6 img/s
4232.3 img/s
4473.0 img/s
4781.9 img/s
Total average 4347.2 img/s
Let us check the output images with their augmentations! Tensorflow outputs numpy arrays, so we can visualize them easily with matplotlib
.
We define a show_images
helper function that will display a sample of our batch.
The batch layout is NCHW so we use transpose to get HWC images, that matplotlib
can show.
[8]:
from __future__ import division
import matplotlib.gridspec as gridspec
import matplotlib.pyplot as plt
%matplotlib inline
def show_images(image_batch, nb_images):
columns = 4
rows = (nb_images + 1) // (columns)
fig = plt.figure(figsize = (32,(32 // columns) * rows))
gs = gridspec.GridSpec(rows, columns)
for j in range(nb_images):
plt.subplot(gs[j])
plt.axis("off")
img = image_batch[0][j].transpose((1,2,0)) + 128
plt.imshow(img.astype('uint8'))
show_images(res[0], 8)
Let us create the same operator for the CPU:
[9]:
class RN50CPUPipeline(Pipeline):
def __init__(self, batch_size, num_threads, device_id, num_gpus):
super(RN50CPUPipeline, self).__init__(batch_size,
num_threads,
device_id)
self.input = ops.MXNetReader(path = rec_files, index_path = idx_files,
shard_id = device_id, num_shards = num_gpus)
self.decode = ops.HostDecoder(device = "cpu", output_type = types.RGB)
self.resize = ops.Resize(device = "cpu",
image_type = types.RGB,
interp_type = types.INTERP_LINEAR)
self.cmn = ops.CropMirrorNormalize(device = "cpu",
output_dtype = types.FLOAT,
crop = (224, 224),
image_type = types.RGB,
mean = [128., 128., 128.],
std = [1., 1., 1.])
self.res_uniform = ops.Uniform(range = (256.,480.))
self.uniform = ops.Uniform(range = (0.0, 1.0))
self.cast = ops.Cast(device = "cpu",
dtype = types.INT32)
def define_graph(self):
inputs, labels = self.input(name="Reader")
images = self.decode(inputs)
images = self.resize(images, resize_shorter = self.res_uniform())
output = self.cmn(images, crop_pos_x = self.uniform(),
crop_pos_y = self.uniform())
output = self.cast(output)
return (output, labels)
cpu_pipes = [RN50CPUPipeline(batch_size=BATCH_SIZE, num_threads=4, device_id = device_id, num_gpus = DEVICES) for device_id in range(DEVICES)]
daliop = dali_tf.DALIIterator()
images_cpu = []
labels_cpu = []
for d in range(DEVICES):
with tf.device('/cpu'):
image_cpu, label_cpu = daliop(pipeline = cpu_pipes[d],
shapes = [(BATCH_SIZE, 3, 224, 224), ()],
dtypes = [tf.int32, tf.float32])
images_cpu.append(image_cpu)
labels_cpu.append(label_cpu)
with tf.Session() as sess:
all_img_per_sec = []
total_batch_size = BATCH_SIZE * DEVICES
for i in range(ITERATIONS):
start_time = time.time()
# The actual run with our dali_tf tensors
res_cpu = sess.run([images_cpu, labels_cpu])
elapsed_time = time.time() - start_time
img_per_sec = total_batch_size / elapsed_time
if i > BURNIN_STEPS:
all_img_per_sec.append(img_per_sec)
print("\t%7.1f img/s" % img_per_sec)
print("Total average %7.1f img/s" % (sum(all_img_per_sec) / len(all_img_per_sec)))
show_images(res_cpu[0], 8)
1725.7 img/s
6788.3 img/s
2740.7 img/s
3229.3 img/s
2966.5 img/s
2908.3 img/s
2976.2 img/s
2816.9 img/s
3099.2 img/s
2725.7 img/s
3659.7 img/s
3078.7 img/s
3061.0 img/s
2979.2 img/s
3014.9 img/s
Total average 3184.7 img/s