Use multiple GPUs in TensorFlow to inference with pb model

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I use a server with 8 Titan X, trying to predict image much faster than use a single one GPU. I load the PB model like this:

model_dir = "./model"
    model = "nasnet_large_v1.pb"
    model_path = os.path.join(model_dir, model)
    model_graph = tf.Graph()
    with model_graph.as_default():
        with tf.gfile.GFile(model_path, 'rb') as f:
            graph_def = tf.GraphDef()
            graph_def.ParseFromString(f.read())
            _ = tf.import_graph_def(graph_def, name='')
            input_layer = model_graph.get_tensor_by_name("input:0")
            output_layer = model_graph.get_tensor_by_name('final_layer/predictions:0')

then I start iterating files in the ./data_input directory like this:

with tf.Session(graph = model_graph, config=config) as inference_session:
        # Initialize session
        initializer = np.zeros([1, 331, 331, 3])
        print("Initialing session...")
        inference_session.run(output_layer, feed_dict={input_layer: initializer})
        print("Done initialing.")

        # Prediction
        file_list = []
        processed_files = []

        for path, dir, files in os.walk('./model_output/processed_files'):
            for file in files:
                processed_files.append(file.split('_')[0]+'.tfrecord')

        print("Processed files: ")
        for f in processed_files:
            print('\t', f)

        while True:
            for path, dir, files in os.walk("./data_input"):
                for file in files:
                    if file == '.DS_Store': continue
                    if file in processed_files: continue
                    print("Reading file {}".format(file))
                    file_path = os.path.join('./data_input', file)
                    file_list.append(file_path)
                    res = predict(file_path)
                    processed_files.append(file)

                    with open('./model_output/processed_files/{}_{}_processed_files.json'.format(file.split('.')[0], model.split('.')[0]), 'w') as f:
                        f.write(json.dumps(processed_files))

                    with open('./model_output/classify_result/{}_{}_classify_result.json'.format(file.split('.')[0], model.split('.')[0]), 'w') as f:
                        f.write(json.dumps(res, indent=4, separators=(',',':')))

            time.sleep(1)

in the predict() function, I wrote code like this:

label_map = get_label()
    # read tfrecord file by tf.data
    dataset = get_dataset(filename)
    # dataset.apply(tf.contrib.data.prefetch_to_device("/gpu:0"))
    # load data
    iterator = dataset.make_one_shot_iterator()
    features = iterator.get_next()

    result = []
    content = {}
    count = 0
    # session
    with tf.Session() as sess:
        tf.global_variables_initializer()
        t1 = time.time()
        try:
            while True:
                [_image, _label, _filepath] = sess.run(fetches=features)
                _image = np.asarray([_image])
                _image = _image.reshape(-1, 331, 331, 3)

                predictions = inference_session.run(output_layer, feed_dict={input_layer: _image})
                predictions = np.squeeze(predictions)

                # res = []
                for i, pred in enumerate(predictions):
                    count += 1
                    overall_result = np.argmax(pred)
                    predict_result = label_map[overall_result].split(":")[-1]

                    if predict_result == 'unknown': continue

                    content['prob'] = str(np.max(pred))
                    content['label'] = predict_result
                    content['filepath'] = str(_filepath[i], encoding='utf-8')
                    result.append(content)

        except tf.errors.OutOfRangeError:
            t2 = time.time()
            print("{} images processed, average time: {}s".format(count, (t2-t1)/count))
    return result

I tried to use with tf.device('/gpu:{}'.format(i)) in the loading model part or the inference session part or the session part, nvidia-smi shows that only GPU0 is use to 100%, while other GPUs doesn't seem to work even when the memory is load.

What should I do to make all the GPUs run at the same time to boost predicting speed?

My code is under https://github.com/tzattack/image_classification_algorithms .

tensorflow gpu python-3.x
2 Answers

you can force the device for each node in the graph by:

def load_network(graph, i):
    od_graph_def = tf.GraphDef()
    with tf.gfile.GFile(graph, 'rb') as fid:
        serialized_graph = fid.read()
    od_graph_def.ParseFromString(serialized_graph)
    for node in od_graph_def.node:
        node.device = '/gpu:{}'.format(i) if i >= 0 else '/cpu:0'
    return {"od_graph_def": od_graph_def}

then you can merge the multiple grapgh you got (per gpu) to one
also change the tensor names in case you are using the same model for all gpus
and run all in one sessoin

works perfectly for me

user_71365160

It can be done as follows:

def get_frozen_graph(graph_file):
    """Read Frozen Graph file from disk."""
    with tf.gfile.GFile(graph_file, "rb") as f:
        graph_def = tf.GraphDef()
        graph_def.ParseFromString(f.read())
    return graph_def

trt_graph1 = get_frozen_graph('/home/ved/ved_1/frozen_inference_graph.pb')

with tf.device('/gpu:1'):
    [tf_input_l1, tf_scores_l1, tf_boxes_l1, tf_classes_l1, tf_num_detections_l1, tf_masks_l1] = tf.import_graph_def(trt_graph1, 
                    return_elements=['image_tensor:0', 'detection_scores:0', 
                    'detection_boxes:0', 'detection_classes:0','num_detections:0', 'detection_masks:0'])
    
tf_sess1 = tf.Session(config=tf.ConfigProto(allow_soft_placement=True))

trt_graph2 = get_frozen_graph('/home/ved/ved_2/frozen_inference_graph.pb')

with tf.device('/gpu:0'):
    [tf_input_l2, tf_scores_l2, tf_boxes_l2, tf_classes_l2, tf_num_detections_l2] = tf.import_graph_def(trt_graph2, 
                    return_elements=['image_tensor:0', 'detection_scores:0', 
                    'detection_boxes:0', 'detection_classes:0','num_detections:0'])
    
tf_sess2 = tf.Session(config=tf.ConfigProto(allow_soft_placement=True))
user_45827110
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