# Quick demo¶

Colossal-AI is an integrated large-scale deep learning system with efficient parallelization techniques. The system can accelerate model training on distributed systems with multiple GPUs by applying parallelization techniques. The system can also run on systems with only one GPU. Quick demos showing how to use Colossal-AI are given below.

## Single GPU¶

Colossal-AI can be used to train deep learning models on systems with only one GPU and achieve baseline performances. We provided an example to train ResNet on CIFAR10 data with only one GPU. You can find this example in examples\resnet_cifar10_data_parallel in the repository. Detailed instructions can be found in its README.md.

## Multiple GPUs¶

Colossal-AI can be used to train deep learning models on distributed systems with multiple GPUs and accelerate the training process drastically by applying efficient parallelization techiniques, which will be elaborated in the Parallelization section below.

You can turn the resnet example mentioned above into a multi-GPU training by setting --nproc_per_node to be the number of GPUs you have on your system. We also provide an example of Vision Transformer which relies on training with more GPUs. You can visit this example in examples\vit_b16_imagenet_data_parallel. It has a detailed instructional README.md for you too.

## Sample Training Script¶

Below is a typical way of how you train the model using

import colossalai
from colossalai.amp import AMP_TYPE
from colossalai.logging import get_dist_logger
from colossalai.trainer import Trainer, hooks

CONFIG = dict(
parallel=dict(
pipeline=1,
tensor=1, mode=None
),
fp16 = dict(
mode=AMP_TYPE.TORCH
),
)

def run_trainer():
parser = colossalai.get_default_parser()
args = parser.parse_args()
colossalai.launch(config=CONFIG,
rank=args.rank,
world_size=args.world_size,
host=args.host,
port=args.port,
backend=args.backend)

logger = get_dist_logger()

model = MyModel()
optimizer = MyOptimizer(model.parameters(), ...)
train_dataset = TrainDataset()
test_dataset = TestDataset()
lr_scheduler = MyScheduler()
logger.info("components are built")

optimizer,
criterion,
lr_scheduler)

trainer = Trainer(engine=engine,
verbose=True)

hook_list = [
hooks.LossHook(),
hooks.LRSchedulerHook(lr_scheduler=lr_scheduler, by_epoch=False),
hooks.AccuracyHook(),
hooks.TensorboardHook(log_dir='./tb_logs', ranks=[0]),
hooks.LogMetricByEpochHook(logger),
hooks.LogMemoryByEpochHook(logger),
hooks.SaveCheckpointHook(checkpoint_dir='./ckpt')
]

trainer.fit(
epochs=NUM_EPOCH,
hooks=hook_list,
display_progress=True,
test_interval=2
)

if __name__ == '__main__':
run_trainer()


Alternatively, the model variable can be substituted with a self-defined model or a pre-defined model in our Model Zoo. The detailed substitution process is elaborated here.

## Features¶

Colossal-AI provides a collection of parallel training components for you. We aim to support you with your development of distributed deep learning models just like how you write single-GPU deep learning models. We provide friendly tools to kickstart distributed training in a few lines.