Supercharge ML experiments with Pytorch Lightning

Machine Learning Singapore

23 Feb 2023

Vivek Kalyan

hello@vivekkalyan.com

@vivekkalyansk

 

 

About Me

AI Research @ Handshakes

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Agenda

  • Why Pytorch-Lightning?
  • Convert Pytorch to Pytorch-Lightning
  • Features
    • Experiment Management
    • Dev Features
    • Memory Features
    • Optimizer Features
    • Deployment
    • .. and more!

Slides: https://slides.com/vivekkalyan/pytorch-lightning

Github: vivekkalyan/pytorch-lightning-examples

Why Pytorch Lightning?

Why Pytorch?

  • Most popular framework for research
  • Stable APIs
  • Pytorch 2.0 release is exciting!
  • Intuitive and explicit ...

Easy to make mistakes in Pytorch

  • "Boilerplate code"
    • call .zero_grad()
    • call .train()/.eval()/.no_grad()
    • call .to(device)

Pytorch Lightning Decouples Engineering & Research Code

  • Research code

    • Model

    • Data

    • Loss + Optimizer

  • Engineering Code

    • Train/Val/Test Loops

    • Everything else ...

Convert Pytorch to

Pytorch Lightning

class Net(LightningModule):
    def __init__(self):
        super(Net, self).__init__()
        self.fc1 = nn.Linear(28 * 28, 128)
        self.fc2 = nn.Linear(128, 10)

    def forward(self, x):
        x = x.view(x.size(0), -1)
        x = self.fc1(x)
        x = F.relu(x)
        x = self.fc2(x)
        output = F.log_softmax(x, dim=1)
        return output

    def train_dataloader(self):
        mnist_train = MNIST(os.getcwd(), train=True, 
            download=True, transform=transforms.ToTensor())
        return DataLoader(mnist_train, batch_size=64)

    def configure_optimizers(self):
        optimizer = Adam(self.parameters(), lr=1e-3)
        return optimizer
      
    def training_step(self, batch, batch_idx):
        data, target = batch
        output = self.forward(data)
        loss = F.nll_loss(output, target)
        return {"loss": loss}

if __name__ == "__main__":
    net = Net()
    trainer = Trainer(accelerator="gpu", max_epochs=10)
    trainer.fit(net)
class Net(nn.Module):
    def __init__(self):
        super(Net, self).__init__()
        self.fc1 = nn.Linear(28 * 28, 128)
        self.fc2 = nn.Linear(128, 10)

    def forward(self, x):
        x = x.view(x.size(0), -1)
        x = self.fc1(x)
        x = F.relu(x)
        x = self.fc2(x)
        output = F.log_softmax(x, dim=1)
        return output

mnist_train = MNIST(os.getcwd(), train=True, download=True, 
    transform=transforms.ToTensor())
train_loader = DataLoader(mnist_train, batch_size=64)

net = Net().to(device)

optimizer = Adam(net.parameters(), lr=1e-3)

for epoch in range(1, 11):
    net.train()
    for batch_idx, (data, target) in enumerate(train_loader):
        data, target = data.to(device), target.to(device)
        optimizer.zero_grad()
        output = net(data)
        loss = F.nll_loss(output, target)

        loss.backward()
        optimizer.step()
        if batch_idx % 50 == 0:
            print("Train Epoch: {} [{}/{} ({:.0f}%)]\t
                Loss: {:.6f}".format(epoch, 
                batch_idx * len(data),
                len(train_loader.dataset),
                100 * batch_idx / len(train_loader),
                loss.item()))

Pytorch

Pytorch Lightning

Features

Experiments Management

  • keeping track of multiple experiments

Logging

  • Automatically creates a folder for each run
  • Saves any values logged with self.log
  • Choose from different loggers
    • Tensorboard
    • Comet
    • MLFlow
    • Neptune
    • Weights and Biases
class Net(LightningModule):
    def __init__(self):
        super(Net, self).__init__()
        self.save_hyperparameters()
        self.fc1 = nn.Linear(28 * 28, 128)
        self.fc2 = nn.Linear(128, 10)

    def forward(self, x):
      	# ... forward

    def train_dataloader(self):
       	# ... train_dataloader

    def configure_optimizers(self):
		# ... configure_optimizers
      
    def training_step(self, batch, batch_idx):
        data, target = batch
        output = self.forward(data)
        loss = F.nll_loss(output, target)
        self.log("loss", loss)
        return {"loss": loss}

if __name__ == "__main__":
    net = Net()
    logger = TensorBoardLogger()
    trainer = Trainer(accelerator="gpu", max_epochs=10, logger=logger)
    trainer.fit(net)

Tensorboard

Tensorboard

$ tensorboard --logdir lightning_logs --port 8888

Validation/Test Dataset

class Net(LightningModule):
    def __init__(self):
        # ... init

    def forward(self, x):
      	# ... forward

    def train_dataloader(self):
       	# ... train_dataloader
    
    def val_dataloader(self):
        mnist_train = MNIST(os.getcwd(), train=False, download=True, 
                          transform=transforms.ToTensor())
        return DataLoader(mnist_train, batch_size=self.batch_size)
      
    def configure_optimizers(self):
		# ... configure_optimizers
      
    def training_step(self, batch, batch_idx):
        # ... training_step
    
    def validation_step(self, batch, batch_idx):
        data, target = batch
        output = self.forward(data)
        loss = F.nll_loss(output, target)
        pred = output.argmax(dim=1, keepdim=True)
        correct = pred.squeeze(1).eq(target).sum().item()
        self.log("val/loss", loss)
        return {"loss": loss, "correct": correct, "total": len(target)}

    def validation_epoch_end(self, outs):
        num_correct = sum(map(lambda x: x[f"correct"], outs), 0)
        num_total = sum(map(lambda x: x[f"total"], outs), 0)
        self.log("val/accuracy", num_correct / num_total)
      

if __name__ == "__main__":
    # ...

Metrics

class Net(LightningModule):
    def __init__(self):
        # ... init

    def forward(self, x):
      	# ... forward

    def train_dataloader(self):
       	# ... train_dataloader
    
    def val_dataloader(self):
        # ... val_dataloader
      
    def configure_optimizers(self):
		# ... configure_optimizers
	
    def on_train_start(self):
        self.logger.log_hyperparams(self.hparams, {"val/accuracy": 0})
      
    def training_step(self, batch, batch_idx):
        # ... training_step
    
    def validation_step(self, batch, batch_idx):
        # ... validation_step

    def validation_epoch_end(self, outs):
        num_correct = sum(map(lambda x: x[f"correct"], outs), 0)
        num_total = sum(map(lambda x: x[f"total"], outs), 0)
        self.log("val/accuracy", num_correct / num_total)
      

if __name__ == "__main__":
    # ...

Metrics

Custom checkpointing

class Net(LightningModule):
	# ... net

if __name__ == "__main__":
    net = Net()
    logger = TensorBoardLogger()
    checkpoint_callback = ModelCheckpoint(monitor='val/accuracy', mode='max', verbose=True)
    trainer = Trainer(callbacks = [checkpoint_callback], accelerator="gpu", max_epochs=10, logger=logger)
    trainer.fit(net)

Early Stopping

class Net(LightningModule):
	# ... net

if __name__ == "__main__":
    net = Net()
    logger = TensorBoardLogger()
    checkpoint_callback = ModelCheckpoint(monitor='val/accuracy', mode='max', verbose=True)
    early_stopping_callback = EarlyStopping(monitor='val/accuracy', mode='max', patience=2)
    trainer = Trainer(callbacks = [early_stopping_callback, checkpoint_callback], 
                      accelerator="gpu", max_epochs=10, logger=logger)
    trainer.fit(net)

Dev Features

  • make development easier

Command line arguments

  • Control model hyper-parameters via CLI
  • Lightning Trainer provides function to expose configuring it through CLI as well
class Net(LightningModule):
    def __init__(self, batch_size, hidden_size, learning_rate, **kwargs):
        # ... init
    
    def add_model_specific_args(parent_parser):
        parser = parent_parser.add_argument_group("Net")
        parser.add_argument("--batch_size", type=int, default=64)
        parser.add_argument("--hidden_size", type=int, default=128)
        parser.add_argument("--learning_rate", type=float, default=1e-3)
        return parent_parser

    def forward(self, x):
      	# ... forward
      

if __name__ == "__main__":
    # ...
    
    parser = ArgumentParser()
    parser = Net.add_model_specific_args(parser)
    parser = Trainer.add_argparse_args(parser)
    args = parser.parse_args()
    
    net = Net(**vars(args))
    
    trainer = Trainer.from_argparse_args(args)
    
    trainer.fit(net)

Fast Dev Run

  • Run one batch of train/val/test
    • Useful to verify pipeline works before starting long run
$ python train.py --fast_dev_run

Overfit batch

  • Overfits training against small % of dataset
    • Sanity check to verify that loss is decreasing ~ model is learning
$ python train.py --overfit_batches 0.01

Learning Rate Finder

class Net(LightningModule):
	# ... net

if __name__ == "__main__":
    net = Net()
    trainer = Trainer(accelerator="gpu", max_epochs=10)
 
    # Run learning rate finder
    lr_finder = trainer.tuner.lr_find(model)

    # Plot with
    fig = lr_finder.plot(suggest=True)
    fig.show()
  • Increase learning rate is for each batch and corresponding loss is logged
  • Plot learning rate vs loss
  • Suggest learning rate at highest rate of loss decrease

Memory Features

Emergent Abilities of Large Language Models

Emergent Abilities of Large Language Models (Wei et al., 2022)

Precision 16

  • Using fp16 instead of fp32 for parameters
    • fit larger models/batches on GPU for ~ free
    • increases training speed for ~ free
$ python train.py --precision 16

Acculumate Gradients

  • Calculate gradients for N batches before updating parameters
  • Effective batch size = batch_size * N
$ python train.py --accumulate_grad_batches 4

Optimizer Features

Gradient Clipping

  • Clip gradients above set value.
    • Helps to prevent exploding gradients
$ python train.py --gradient_clip_val 1

Stochastic Weight Averaging

  • Helps prevent loss being stuck in local minimum
class Net(LightningModule):
	# ... net

if __name__ == "__main__":
    net = Net()
    logger = TensorBoardLogger()
    swa_callback = StochasticWeightAveraging(swa_lrs=1e-2)
    trainer = Trainer(callbacks = [swa_callback], 
                      accelerator="gpu", max_epochs=10, logger=logger)
    trainer.fit(net)

Quantization Aware Training (beta)

  • Models quantization errors in both the forward and backward passes using fake-quantization modules.
  • After training, model is converted to lower precision

Deployment

  • export to multiple formats

Predict with Pure Pytorch

  • Swap pl.LightningModule -> nn.Module
  • No Lightning dependency for prediction
    • access to entire ecosystem of Pytorch deployment
class Net(nn.Module):
    def __init__(self):
        super(Net, self).__init__()
        self.fc1 = nn.Linear(28 * 28, 128)
        self.fc2 = nn.Linear(128, 10)

    def forward(self, x):
        x = x.view(x.size(0), -1)
        x = self.fc1(x)
        x = F.relu(x)
        x = self.fc2(x)
        output = F.log_softmax(x, dim=1)
        return output

model = Net()
checkpoint = torch.load("path/to/lightning/checkpoint.ckpt")
model.load_state_dict(checkpoint["state_dict"])
model.eval()

... and more!

  • Profilers
  • Quantization/Pruning
  • (Distributed) GPU optimizations
  • ...

Thank you!

pytorch-lightning

By vivekkalyan

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