When your memory can fit the model, you can use the first two methods to build your model, otherwise you must split the model by yourself. The first two methods first build the whole model on CPU, then split the model, and finally you can just move the corresponding part of model to GPU.
`colossalai.builder.build_pipeline_model_from_cfg()` receives a config file of model, and it can split the model uniformly (by layer) or balanced (by parameter size).
`colossalai.legacy.builder.build_pipeline_model_from_cfg()` receives a config file of model, and it can split the model uniformly (by layer) or balanced (by parameter size).
If you are familiar with `PyTorch`, you can use `colossalai.builder.build_pipeline_model()` which receives a `torch.nn.Sequential` model and split it by layer uniformly.
If you are familiar with `PyTorch`, you can use `colossalai.legacy.builder.build_pipeline_model()` which receives a `torch.nn.Sequential` model and split it by layer uniformly.
In this tutorial, we will modify [TIMM/ViT](https://github.com/rwightman/pytorch-image-models/blob/master/timm/models/vision_transformer.py) to `torch.nn.Sequential` and then use `colossalai.builder.build_pipeline_model()` to build the pipelined model.
In this tutorial, we will modify [TIMM/ViT](https://github.com/rwightman/pytorch-image-models/blob/master/timm/models/vision_transformer.py) to `torch.nn.Sequential` and then use `colossalai.legacy.builder.build_pipeline_model()` to build the pipelined model.
When the data is **one**`Tensor`, you can use the positional argument in `forward()` of your model to get the data tensor. For the first stage of pipeline, the first positional argument of `forward()` is the data tensor loaded from data loader. For other stages, the first positional argument of `forward()` is the output tensor from the previous stage. Note that if the stage is not the last stage, the return of `forward()` must be a `Tensor`.
