MosaicML Composer

Composer is a library for training neural networks better, faster, and cheaper. It contains many state-of-the-art methods for accelerating neural network training and improving generalization, along with an optional Trainer API that makes composing many different enhancements easy.

W&B provides a lightweight wrapper for logging your ML experiments. But you don't need to combine the two yourself: Weights & Biases is incorporated directly into the Composer library via the WandBLogger.

Start logging to W&B with two lines of code

from composer import Trainer
from composer.loggers import WandBLogger

wandb_logger = WandBLogger(init_params=init_params)
trainer = Trainer(..., logger=wandb_logger)

Using Composer's WandBLogger

Composer library has the WandBLogger class that can be used along the Trainer to log metrics to Weights and Biases. It is a simple as instantiating the logger and passing it to the Trainer

wandb_logger = WandBLogger()
trainer = Trainer(logger=wandb_logger)

Logger arguments

Below are some of the most used parameters in WandbLogger, see the Composer documentation for a full list and description

Parameter	Description
init_params	Params to pass to wandb.init such as your wandb project, entity, name or config etc See here for the full list wandb.init accepts
log_artifacts	Whether to log checkpoints to wandb
log_artifacts_every_n_batches	Interval at which to upload Artifacts. Only applicable when log_artifacts=True
rank_zero_only	Whether to log only on the rank-zero process. When logging artifacts **** to wandb, it is highly recommended to log on all ranks. Artifacts from ranks ≥1 will not be stored, which may discard pertinent information. For example, when using DeepSpeed ZeRO, it would be impossible to restore from checkpoints without artifacts from all ranks (default: False).

A typical usage would be:

init_params = {"project":"composer", 
               "name":"imagenette_benchmark",
               "config":{"arch":"Resnet50",
                         "use_mixed_precision":True
                         }
               }

wandb_logger = WandBLogger(log_artifacts=True, init_params=init_params)

Log prediction samples

You can use Composer's Callbacks system to control when you log to Weights & Biases via the WandBLogger, in this example we log a sample of our validation images and predictions:

import wandb
from composer import Callback, State, Logger

class LogPredictions(Callback):
    def __init__(self, num_samples=100, seed=1234):
        super().__init__()
        self.num_samples = num_samples
        self.data = []
        
    def eval_batch_end(self, state: State, logger: Logger):
        """Compute predictions per batch and stores them on self.data"""
        
        if state.timer.epoch == state.max_duration: #on last val epoch
            if len(self.data) < self.num_samples:
                n = self.num_samples
                x, y = state.batch_pair
                outputs = state.outputs.argmax(-1)
                data = [[wandb.Image(x_i), y_i, y_pred] for x_i, y_i, y_pred in list(zip(x[:n], y[:n], outputs[:n]))]
                self.data += data
            
    def eval_end(self, state: State, logger: Logger):
        "Create a wandb.Table and logs it"
        columns = ['image', 'ground truth', 'prediction']
        table = wandb.Table(columns=columns, data=self.data[:self.num_samples])
        wandb.log({'sample_table':table}, step=int(state.timer.batch))         
...

trainer = Trainer(
    ...
    loggers=[WandBLogger()],
    callbacks=[LogPredictions()]
)