Update to use torchrun in "brats_training_ddp" (#1666)

Fixes #1665

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---------

Signed-off-by: YunLiu <[email protected]>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

acceleration/README.md

@@ -6,7 +6,7 @@ Typically, model training is a time-consuming step during deep learning developm
 The document introduces details of how to profile the training pipeline, how to analyze the dataset and select suitable algorithms, and how to optimize GPU utilization in single GPU, multi-GPUs or even multi-nodes.
 #### [distributed_training](./distributed_training)
 The examples show how to execute distributed training and evaluation based on 3 different frameworks:
-- PyTorch native `DistributedDataParallel` module with `torch.distributed.launch`.
+- PyTorch native `DistributedDataParallel` module with `torchrun`.
 - Horovod APIs with `horovodrun`.
 - PyTorch ignite and MONAI workflows.
 

acceleration/distributed_training/brats_training_ddp.py

@@ -22,31 +22,28 @@
 
 Main steps to set up the distributed training:
 
-- Execute `torch.distributed.launch` to create processes on every node for every GPU.
+- Execute `torchrun` to create processes on every node for every GPU.
   It receives parameters as below:
   `--nproc_per_node=NUM_GPUS_PER_NODE`
   `--nnodes=NUM_NODES`
-  `--node_rank=INDEX_CURRENT_NODE`
   `--master_addr="localhost"`
   `--master_port=1234`
-  For more details, refer to https://github.com/pytorch/pytorch/blob/master/torch/distributed/launch.py.
+  For more details, refer to https://github.com/pytorch/pytorch/blob/master/torch/distributed/run.py.
   Alternatively, we can also use `torch.multiprocessing.spawn` to start program, but it that case, need to handle
   all the above parameters and compute `rank` manually, then set to `init_process_group`, etc.
-  `torch.distributed.launch` is even more efficient than `torch.multiprocessing.spawn` during training.
+  `torchrun` is even more efficient than `torch.multiprocessing.spawn` during training.
 - Use `init_process_group` to initialize every process, every GPU runs in a separate process with unique rank.
-  Here we use `NVIDIA NCCL` as the backend and must set `init_method="env://"` if use `torch.distributed.launch`.
+  Here we use `NVIDIA NCCL` as the backend and must set `init_method="env://"` if use `torchrun`.
 - Wrap the model with `DistributedDataParallel` after moving to expected device.
 - Partition dataset before training, so every rank process will only handle its own data partition.
 
 Note:
-    `torch.distributed.launch` will launch `nnodes * nproc_per_node = world_size` processes in total.
+    `torchrun` will launch `nnodes * nproc_per_node = world_size` processes in total.
     Suggest setting exactly the same software environment for every node, especially `PyTorch`, `nccl`, etc.
     A good practice is to use the same MONAI docker image for all nodes directly.
     Example script to execute this program on every node:
-    python -m torch.distributed.launch --nproc_per_node=NUM_GPUS_PER_NODE
-           --nnodes=NUM_NODES --node_rank=INDEX_CURRENT_NODE
-           --master_addr="localhost" --master_port=1234
-           brats_training_ddp.py -d DIR_OF_TESTDATA
+    python -m torchrun --nproc_per_node=NUM_GPUS_PER_NODE --nnodes=NUM_NODES
+        --master_addr="localhost" --master_port=1234 brats_training_ddp.py -d DIR_OF_TESTDATA
 
     This example was tested with [Ubuntu 16.04/20.04], [NCCL 2.6.3].
 
@@ -162,15 +159,15 @@ def _generate_data_list(self, dataset_dir):
 
 def main_worker(args):
     # disable logging for processes except 0 on every node
-    if args.local_rank != 0:
+    if int(os.environ["LOCAL_RANK"]) != 0:
         f = open(os.devnull, "w")
         sys.stdout = sys.stderr = f
     if not os.path.exists(args.dir):
         raise FileNotFoundError(f"missing directory {args.dir}")
 
     # initialize the distributed training process, every GPU runs in a process
     dist.init_process_group(backend="nccl", init_method="env://")
-    device = torch.device(f"cuda:{args.local_rank}")
+    device = torch.device(f"cuda:{os.environ['LOCAL_RANK']}")
     torch.cuda.set_device(device)
     # use amp to accelerate training
     scaler = torch.cuda.amp.GradScaler()
@@ -364,8 +361,6 @@ def evaluate(model, val_loader, dice_metric, dice_metric_batch, post_trans):
 def main():
     parser = argparse.ArgumentParser()
     parser.add_argument("-d", "--dir", default="./testdata", type=str, help="directory of Brain Tumor dataset")
-    # must parse the command-line argument: ``--local_rank=LOCAL_PROCESS_RANK``, which will be provided by DDP
-    parser.add_argument("--local_rank", type=int, help="node rank for distributed training")
     parser.add_argument("--epochs", default=300, type=int, metavar="N", help="number of total epochs to run")
     parser.add_argument("--lr", default=1e-4, type=float, help="learning rate")
     parser.add_argument("-b", "--batch_size", default=1, type=int, help="mini-batch size of every GPU")
@@ -388,12 +383,9 @@ def main():
     main_worker(args=args)
 
 
-# usage example(refer to https://github.com/pytorch/pytorch/blob/master/torch/distributed/launch.py):
+# usage example(refer to https://github.com/pytorch/pytorch/blob/main/torch/distributed/run.py):
 
-# python -m torch.distributed.launch --nproc_per_node=NUM_GPUS_PER_NODE
-#        --nnodes=NUM_NODES --node_rank=INDEX_CURRENT_NODE
-#        --master_addr="localhost" --master_port=1234
-#        brats_training_ddp.py -d DIR_OF_TESTDATA
+# torchrun --nproc_per_node=NUM_GPUS_PER_NODE --nnodes=NUM_NODES brats_training_ddp.py -d DIR_OF_TESTDATA
 
 if __name__ == "__main__":
     main()