【tensorflow2.0】使用单GPU训练模型

深度学习的训练过程常常非常耗时，一个模型训练几个小时是家常便饭，训练几天也是常有的事情，有时候甚至要训练几十天。

训练过程的耗时主要来自于两个部分，一部分来自数据准备，另一部分来自参数迭代。

当数据准备过程还是模型训练时间的主要瓶颈时，我们可以使用更多进程来准备数据。

当参数迭代过程成为训练时间的主要瓶颈时，我们通常的方法是应用GPU或者Google的TPU来进行加速。

详见《用GPU加速Keras模型——Colab免费GPU使用攻略》

https://zhuanlan.zhihu.com/p/68509398

无论是内置fit方法，还是自定义训练循环，从CPU切换成单GPU训练模型都是非常方便的，无需更改任何代码。当存在可用的GPU时，如果不特意指定device，tensorflow会自动优先选择使用GPU来创建张量和执行张量计算。

但如果是在公司或者学校实验室的服务器环境，存在多个GPU和多个使用者时，为了不让单个同学的任务占用全部GPU资源导致其他同学无法使用（tensorflow默认获取全部GPU的全部内存资源权限，但实际上只使用一个GPU的部分资源），我们通常会在开头增加以下几行代码以控制每个任务使用的GPU编号和显存大小，以便其他同学也能够同时训练模型。

在Colab笔记本中：修改->笔记本设置->硬件加速器 中选择 GPU

注：以下代码只能在Colab 上才能正确执行。

可通过以下colab链接测试效果《tf_单GPU》：

https://colab.research.google.com/drive/1r5dLoeJq5z01sU72BX2M5UiNSkuxsEFe

%tensorflow_version 2.x
import tensorflow as tf
print(tf.__version__)
from tensorflow.keras import * 
 
# 打印时间分割线
@tf.function
def printbar():
    ts = tf.timestamp()
    today_ts = ts%(24*60*60)
 
    hour = tf.cast(today_ts//3600+8,tf.int32)%tf.constant(24)
    minite = tf.cast((today_ts%3600)//60,tf.int32)
    second = tf.cast(tf.floor(today_ts%60),tf.int32)
 
    def timeformat(m):
        if tf.strings.length(tf.strings.format("{}",m))==1:
            return(tf.strings.format("0{}",m))
        else:
            return(tf.strings.format("{}",m))
 
    timestring = tf.strings.join([timeformat(hour),timeformat(minite),
                timeformat(second)],separator = ":")
    tf.print("=========="*8,end = "")
    tf.print(timestring)

一，GPU设置

gpus = tf.config.list_physical_devices("GPU")
 
if gpus:
    gpu0 = gpus[0] #如果有多个GPU，仅使用第0个GPU
    tf.config.experimental.set_memory_growth(gpu0, True) #设置GPU显存用量按需使用
    # 或者也可以设置GPU显存为固定使用量(例如：4G)
    #tf.config.experimental.set_virtual_device_configuration(gpu0,
    #    [tf.config.experimental.VirtualDeviceConfiguration(memory_limit=4096)]) 
    tf.config.set_visible_devices([gpu0],"GPU") 
#比较GPU和CPU的计算速度

printbar()
with tf.device("/gpu:0"):
    tf.random.set_seed(0)
    a = tf.random.uniform((10000,100),minval = 0,maxval = 3.0)
    b = tf.random.uniform((100,100000),minval = 0,maxval = 3.0)
    c = a@b
    tf.print(tf.reduce_sum(tf.reduce_sum(c,axis = 0),axis=0))
printbar()

printbar()
with tf.device("/cpu:0"):
    tf.random.set_seed(0)
    a = tf.random.uniform((10000,100),minval = 0,maxval = 3.0)
    b = tf.random.uniform((100,100000),minval = 0,maxval = 3.0)
    c = a@b
    tf.print(tf.reduce_sum(tf.reduce_sum(c,axis = 0),axis=0))
printbar()

================================================================================11:59:21
2.24953778e+11
================================================================================11:59:23
================================================================================11:59:23
2.24953795e+11
================================================================================11:59:29

二，准备数据

MAX_LEN = 300
BATCH_SIZE = 32
(x_train,y_train),(x_test,y_test) = datasets.reuters.load_data()
x_train = preprocessing.sequence.pad_sequences(x_train,maxlen=MAX_LEN)
x_test = preprocessing.sequence.pad_sequences(x_test,maxlen=MAX_LEN)
 
MAX_WORDS = x_train.max()+1
CAT_NUM = y_train.max()+1
 
ds_train = tf.data.Dataset.from_tensor_slices((x_train,y_train)) 
          .shuffle(buffer_size = 1000).batch(BATCH_SIZE) 
          .prefetch(tf.data.experimental.AUTOTUNE).cache()
 
ds_test = tf.data.Dataset.from_tensor_slices((x_test,y_test)) 
          .shuffle(buffer_size = 1000).batch(BATCH_SIZE) 
          .prefetch(tf.data.experimental.AUTOTUNE).cache()

三，定义模型

tf.keras.backend.clear_session()
 
def create_model():
 
    model = models.Sequential()
 
    model.add(layers.Embedding(MAX_WORDS,7,input_length=MAX_LEN))
    model.add(layers.Conv1D(filters = 64,kernel_size = 5,activation = "relu"))
    model.add(layers.MaxPool1D(2))
    model.add(layers.Conv1D(filters = 32,kernel_size = 3,activation = "relu"))
    model.add(layers.MaxPool1D(2))
    model.add(layers.Flatten())
    model.add(layers.Dense(CAT_NUM,activation = "softmax"))
    return(model)
 
model = create_model()
model.summary()

Model: "sequential"
_________________________________________________________________
Layer (type)                 Output Shape              Param #   
=================================================================
embedding (Embedding)        (None, 300, 7)            216874    
_________________________________________________________________
conv1d (Conv1D)              (None, 296, 64)           2304      
_________________________________________________________________
max_pooling1d (MaxPooling1D) (None, 148, 64)           0         
_________________________________________________________________
conv1d_1 (Conv1D)            (None, 146, 32)           6176      
_________________________________________________________________
max_pooling1d_1 (MaxPooling1 (None, 73, 32)            0         
_________________________________________________________________
flatten (Flatten)            (None, 2336)              0         
_________________________________________________________________
dense (Dense)                (None, 46)                107502    
=================================================================
Total params: 332,856
Trainable params: 332,856
Non-trainable params: 0
_________________________________________________________________

四，训练模型

optimizer = optimizers.Nadam()
loss_func = losses.SparseCategoricalCrossentropy()
 
train_loss = metrics.Mean(name='train_loss')
train_metric = metrics.SparseCategoricalAccuracy(name='train_accuracy')
 
valid_loss = metrics.Mean(name='valid_loss')
valid_metric = metrics.SparseCategoricalAccuracy(name='valid_accuracy')
 
@tf.function
def train_step(model, features, labels):
    with tf.GradientTape() as tape:
        predictions = model(features,training = True)
        loss = loss_func(labels, predictions)
    gradients = tape.gradient(loss, model.trainable_variables)
    optimizer.apply_gradients(zip(gradients, model.trainable_variables))
 
    train_loss.update_state(loss)
    train_metric.update_state(labels, predictions)
 
@tf.function
def valid_step(model, features, labels):
    predictions = model(features)
    batch_loss = loss_func(labels, predictions)
    valid_loss.update_state(batch_loss)
    valid_metric.update_state(labels, predictions)
 
 
def train_model(model,ds_train,ds_valid,epochs):
    for epoch in tf.range(1,epochs+1):
 
        for features, labels in ds_train:
            train_step(model,features,labels)
 
        for features, labels in ds_valid:
            valid_step(model,features,labels)
 
        logs = 'Epoch={},Loss:{},Accuracy:{},Valid Loss:{},Valid Accuracy:{}'
 
        if epoch%1 ==0:
            printbar()
            tf.print(tf.strings.format(logs,
            (epoch,train_loss.result(),train_metric.result(),valid_loss.result(),valid_metric.result())))
            tf.print("")
 
        train_loss.reset_states()
        valid_loss.reset_states()
        train_metric.reset_states()
        valid_metric.reset_states()
 
train_model(model,ds_train,ds_test,10)

================================================================================12:01:11
Epoch=1,Loss:2.00887108,Accuracy:0.470273882,Valid Loss:1.6704694,Valid Accuracy:0.566340148

================================================================================12:01:13
Epoch=2,Loss:1.47044504,Accuracy:0.618681788,Valid Loss:1.51738906,Valid Accuracy:0.630454123

================================================================================12:01:14
Epoch=3,Loss:1.1620506,Accuracy:0.700289488,Valid Loss:1.52190566,Valid Accuracy:0.641139805

================================================================================12:01:16
Epoch=4,Loss:0.878907442,Accuracy:0.771654427,Valid Loss:1.67911685,Valid Accuracy:0.644256473

================================================================================12:01:17
Epoch=5,Loss:0.647668123,Accuracy:0.836450696,Valid Loss:1.93839979,Valid Accuracy:0.642475486

================================================================================12:01:19
Epoch=6,Loss:0.487838209,Accuracy:0.880538881,Valid Loss:2.20062685,Valid Accuracy:0.642030299

================================================================================12:01:21
Epoch=7,Loss:0.390418053,Accuracy:0.90670228,Valid Loss:2.32795334,Valid Accuracy:0.646482646

================================================================================12:01:22
Epoch=8,Loss:0.328294098,Accuracy:0.92351371,Valid Loss:2.44113493,Valid Accuracy:0.644701719

================================================================================12:01:24
Epoch=9,Loss:0.286735713,Accuracy:0.931195736,Valid Loss:2.5071857,Valid Accuracy:0.642920732

================================================================================12:01:25
Epoch=10,Loss:0.256434649,Accuracy:0.936428428,Valid Loss:2.60177088,Valid Accuracy:0.640249312

参考：

开源电子书地址：https://lyhue1991.github.io/eat_tensorflow2_in_30_days/

GitHub 项目地址：https://github.com/lyhue1991/eat_tensorflow2_in_30_days