Using PyTorch DALI plugin: using various readers

Overview

This example shows how different readers could be used to interact with PyTorch. It shows how flexible DALI is.

The following readers are used in this example:

• MXNetReader

• CaffeReader

• FileReader

• TFRecordReader

For details on how to use them please see other examples.

Let us start from defining some global constants

# MXNet RecordIO
db_folder = "/data/imagenet/train-480-val-256-recordio/"

# Caffe LMDB
lmdb_folder = "/data/imagenet/train-lmdb-256x256"

# image dir with plain jpeg files
image_dir = "../images"

# TFRecord
tfrecord = "/data/imagenet/train-val-tfrecord-480/train-00001-of-01024"
tfrecord_idx = "idx_files/train-00001-of-01024.idx"
tfrecord2idx_script = "tfrecord2idx"

N = 8             # number of GPUs
BATCH_SIZE = 128  # batch size per GPU
ITERATIONS = 32
IMAGE_SIZE = 3

Create idx file by calling tfrecord2idx script

from subprocess import call
import os.path

if not os.path.exists("idx_files"):
    os.mkdir("idx_files")

if not os.path.isfile(tfrecord_idx):
    call([tfrecord2idx_script, tfrecord, tfrecord_idx])

Let us define: - common part of pipeline, other pipelines will inherit it

from nvidia.dali.pipeline import Pipeline
import nvidia.dali.ops as ops
import nvidia.dali.types as types

class CommonPipeline(Pipeline):
    def __init__(self, batch_size, num_threads, device_id):
        super(CommonPipeline, self).__init__(batch_size, num_threads, device_id)

        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 = (227, 227),
                                            image_type = types.RGB,
                                            mean = [128., 128., 128.],
                                            std = [1., 1., 1.])
        self.uniform = ops.Uniform(range = (0.0, 1.0))
        self.resize_rng = ops.Uniform(range = (256, 480))

    def base_define_graph(self, inputs, labels):
        images = self.decode(inputs)
        images = self.resize(images, resize_shorter = self.resize_rng())
        output = self.cmn(images, crop_pos_x = self.uniform(),
                          crop_pos_y = self.uniform())
        return (output, labels)

• MXNetReaderPipeline

from nvidia.dali.pipeline import Pipeline
import nvidia.dali.ops as ops
import nvidia.dali.types as types

class MXNetReaderPipeline(CommonPipeline):
    def __init__(self, batch_size, num_threads, device_id, num_gpus):
        super(MXNetReaderPipeline, self).__init__(batch_size, num_threads, device_id)
        self.input = ops.MXNetReader(path = [db_folder+"train.rec"], index_path=[db_folder+"train.idx"],
                                     random_shuffle = True, shard_id = device_id, num_shards = num_gpus)

    def define_graph(self):
        images, labels = self.input(name="Reader")
        return self.base_define_graph(images, labels)

• CaffeReadPipeline

class CaffeReadPipeline(CommonPipeline):
    def __init__(self, batch_size, num_threads, device_id, num_gpus):
        super(CaffeReadPipeline, self).__init__(batch_size, num_threads, device_id)
        self.input = ops.CaffeReader(path = lmdb_folder,
                                     random_shuffle = True, shard_id = device_id, num_shards = num_gpus)

    def define_graph(self):
        images, labels = self.input(name="Reader")
        return self.base_define_graph(images, labels)

• FileReadPipeline

class FileReadPipeline(CommonPipeline):
        def __init__(self, batch_size, num_threads, device_id, num_gpus):
            super(FileReadPipeline, self).__init__(batch_size, num_threads, device_id)
            self.input = ops.FileReader(file_root = image_dir)

        def define_graph(self):
            images, labels = self.input(name="Reader")
            return self.base_define_graph(images, labels)

• TFRecordPipeline

import nvidia.dali.tfrecord as tfrec

class TFRecordPipeline(CommonPipeline):
    def __init__(self, batch_size, num_threads, device_id, num_gpus):
        super(TFRecordPipeline, self).__init__(batch_size, num_threads, device_id)
        self.input = ops.TFRecordReader(path = tfrecord,
                                        index_path = tfrecord_idx,
                                        features = {"image/encoded" : tfrec.FixedLenFeature((), tfrec.string, ""),
                                                    "image/class/label": tfrec.FixedLenFeature([1], tfrec.int64,  -1)
                                        })

    def define_graph(self):
        inputs = self.input(name="Reader")
        images = inputs["image/encoded"]
        labels = inputs["image/class/label"]
        return self.base_define_graph(images, labels)

Let us create pipelines and pass them to PyTorch generic iterator

from __future__ import print_function
import numpy as np
from nvidia.dali.plugin.pytorch import DALIGenericIterator

pipe_types = [[MXNetReaderPipeline, (0, 999)],
              [CaffeReadPipeline, (0, 999)],
              [FileReadPipeline, (0, 1)],
              [TFRecordPipeline, (1, 1000)]]
for pipe_t in pipe_types:
    pipe_name, label_range = pipe_t
    print ("RUN: "  + pipe_name.__name__)
    pipes = [pipe_name(batch_size=BATCH_SIZE, num_threads=2, device_id = device_id, num_gpus = N) for device_id in range(N)]
    pipes[0].build()
    dali_iter = DALIGenericIterator(pipes, ['data', 'label'], pipes[0].epoch_size("Reader"))

    for i, data in enumerate(dali_iter):
        if i >= ITERATIONS:
            break
        # Testing correctness of labels
        for d in data:
            label = d["label"]
            image = d["data"]
            ## labels need to be integers
            assert(np.equal(np.mod(label, 1), 0).all())
            ## labels need to be in range pipe_name[2]
            assert((label >= label_range[0]).all())
            assert((label <= label_range[1]).all())
    print("OK : " + pipe_name.__name__)

RUN: MXNetReaderPipeline
OK : MXNetReaderPipeline
RUN: CaffeReadPipeline
OK : CaffeReadPipeline
RUN: FileReadPipeline
OK : FileReadPipeline
RUN: TFRecordPipeline
OK : TFRecordPipeline