mmselfsup/docs/en/get_started.md

# Getting Started

- [Getting Started](#getting-started)
  - [Train existing methods](#train-existing-methods)
    - [Training with CPU](#training-with-cpu)
    - [Train with single/multiple GPUs](#train-with-singlemultiple-gpus)
    - [Train with multiple machines](#train-with-multiple-machines)
    - [Launch multiple jobs on a single machine](#launch-multiple-jobs-on-a-single-machine)
  - [Benchmarks](#benchmarks)
  - [Tools and Tips](#tools-and-tips)
    - [Count number of parameters](#count-number-of-parameters)
    - [Publish a model](#publish-a-model)
    - [Use t-SNE](#use-t-sne)
    - [Reproducibility](#reproducibility)

This page provides basic tutorials about the usage of MMSelfSup. For installation instructions, please see [install.md](install.md).

## Train existing methods

**Note**: The default learning rate in config files is for 8 GPUs. If using different number GPUs, the total batch size will change in proportion, you have to scale the learning rate following `new_lr = old_lr * new_ngpus / old_ngpus`. We recommend to use `tools/dist_train.sh` even with 1 gpu, since some methods do not support non-distributed training.

### Training with CPU

```shell
export CUDA_VISIBLE_DEVICES=-1
python tools/train.py ${CONFIG_FILE}
```

**Note**: We do not recommend users to use CPU for training because it is too slow and some algorithms are using `SyncBN` which is based on distributed training. We support this feature to allow users to debug on machines without GPU for convenience.

### Train with single/multiple GPUs

```shell
sh tools/dist_train.sh ${CONFIG_FILE} ${GPUS} --work-dir ${YOUR_WORK_DIR} [optional arguments]
```

Optional arguments are:

- `--resume-from ${CHECKPOINT_FILE}`: Resume from a previous checkpoint file.
- `--deterministic`: Switch on "deterministic" mode which slows down training but the results are reproducible.

An example:

```shell
# checkpoints and logs saved in WORK_DIR=work_dirs/selfsup/odc/odc_resnet50_8xb64-steplr-440e_in1k/
sh tools/dist_train.sh configs/selfsup/odc/odc_resnet50_8xb64-steplr-440e_in1k.py 8 --work-dir work_dirs/selfsup/odc/odc_resnet50_8xb64-steplr-440e_in1k/
```

**Note**: During training, checkpoints and logs are saved in the same folder structure as the config file under `work_dirs/`. Custom work directory is not recommended since evaluation scripts infer work directories from the config file name. If you want to save your weights somewhere else, please use symlink, for example:

```shell
ln -s ${YOUR_WORK_DIRS} ${MMSELFSUP}/work_dirs
```

Alternatively, if you run MMSelfSup on a cluster managed with [slurm](https://slurm.schedmd.com/):

```shell
GPUS_PER_NODE=${GPUS_PER_NODE} GPUS=${GPUS} SRUN_ARGS=${SRUN_ARGS} sh tools/slurm_train.sh ${PARTITION} ${JOB_NAME} ${CONFIG_FILE} ${YOUR_WORK_DIR} [optional arguments]
```

An example:

```shell
GPUS_PER_NODE=8 GPUS=8 sh tools/slurm_train.sh Dummy Test_job configs/selfsup/odc/odc_resnet50_8xb64-steplr-440e_in1k.py work_dirs/selfsup/odc/odc_resnet50_8xb64-steplr-440e_in1k/
```

### Train with multiple machines

If you launch with multiple machines simply connected with ethernet, you can simply run following commands:

On the first machine:

```shell
NNODES=2 NODE_RANK=0 PORT=$MASTER_PORT MASTER_ADDR=$MASTER_ADDR sh tools/dist_train.sh $CONFIG $GPUS
```

On the second machine:

```shell
NNODES=2 NODE_RANK=1 PORT=$MASTER_PORT MASTER_ADDR=$MASTER_ADDR sh tools/dist_train.sh $CONFIG $GPUS
```

Usually it is slow if you do not have high speed networking like InfiniBand.

If you launch with slurm, the command is the same as that on single machine described above, but you need refer to [slurm_train.sh](https://github.com/open-mmlab/mmselfsup/blob/master/tools/slurm_train.sh) to set appropriate parameters and environment variables.

### Launch multiple jobs on a single machine

If you launch multiple jobs on a single machine, e.g., 2 jobs of 4-GPU training on a machine with 8 GPUs, you need to specify different ports (29500 by default) for each job to avoid communication conflict.

If you use `dist_train.sh` to launch training jobs:

```shell
CUDA_VISIBLE_DEVICES=0,1,2,3 PORT=29500 sh tools/dist_train.sh ${CONFIG_FILE} 4 --work-dir tmp_work_dir_1
CUDA_VISIBLE_DEVICES=4,5,6,7 PORT=29501 sh tools/dist_train.sh ${CONFIG_FILE} 4 --work-dir tmp_work_dir_2
```

If you use launch training jobs with slurm, you have two options to set different communication ports:

Option 1:

In `config1.py`:

```python
dist_params = dict(backend='nccl', port=29500)
```

In `config2.py`:

```python
dist_params = dict(backend='nccl', port=29501)
```

Then you can launch two jobs with config1.py and config2.py.

```shell
CUDA_VISIBLE_DEVICES=0,1,2,3 GPUS=4 sh tools/slurm_train.sh ${PARTITION} ${JOB_NAME} config1.py tmp_work_dir_1
CUDA_VISIBLE_DEVICES=4,5,6,7 GPUS=4 sh tools/slurm_train.sh ${PARTITION} ${JOB_NAME} config2.py tmp_work_dir_2
```

Option 2:

You can set different communication ports without the need to modify the configuration file, but have to set the `cfg-options` to overwrite the default port in configuration file.

```shell
CUDA_VISIBLE_DEVICES=0,1,2,3 GPUS=4 sh tools/slurm_train.sh ${PARTITION} ${JOB_NAME} config1.py tmp_work_dir_1 --cfg-options dist_params.port=29500
CUDA_VISIBLE_DEVICES=4,5,6,7 GPUS=4 sh tools/slurm_train.sh ${PARTITION} ${JOB_NAME} config2.py tmp_work_dir_2 --cfg-options dist_params.port=29501
```

## Benchmarks

We also provide commands to evaluate your pre-trained model on several downstream task, and you can refer to [Benchmarks](./tutorials/6_benchmarks.md) for the details.

## Tools and Tips

### Count number of parameters

```shell
python tools/analysis_tools/count_parameters.py ${CONFIG_FILE}
```

### Publish a model

Before you publish a model, you may want to

- Convert model weights to CPU tensors.
- Delete the optimizer states.
- Compute the hash of the checkpoint file and append the hash id to the filename.

```shell
python tools/model_converters/publish_model.py ${INPUT_FILENAME} ${OUTPUT_FILENAME}
```

### Use t-SNE

We provide an off-the-shelf tool to visualize the quality of image representations by t-SNE.

```shell
python tools/analysis_tools/visualize_tsne.py ${CONFIG_FILE} --checkpoint ${CKPT_PATH} --work-dir ${WORK_DIR} [optional arguments]
```

Arguments:

- `CONFIG_FILE`: config file for the pre-trained model.
- `CKPT_PATH`: the path of model's checkpoint.
- `WORK_DIR`: the directory to save the results of visualization.
- `[optional arguments]`: for optional arguments, you can refer to [visualize_tsne.py](https://github.com/open-mmlab/mmselfsup/blob/master/tools/analysis_tools/visualize_tsne.py)

### Reproducibility

If you want to make your performance exactly reproducible, please switch on `--deterministic` to train the final model to be published. Note that this flag will switch off `torch.backends.cudnn.benchmark` and slow down the training speed.