Let's compare the execution of a gpt2 language model training over a small sample of wikitext.
The results are:
| NVlink | Time |
| -----  | ---: |
| Y      | 101s |
| N      | 131s |
You can see that NVLink completes the training ~23% faster.
In the second benchmark we use NCCL_P2P_DISABLE=1 to tell the GPUs not to use NVLink.
Here is the full benchmark code and outputs:
```
DDP w/ NVLink
rm -r /tmp/test-clm; CUDA_VISIBLE_DEVICES=0,1 python -m torch.distributed.launch \
--nproc_per_node 2 examples/pytorch/language-modeling/run_clm.py --model_name_or_path gpt2 \
--dataset_name wikitext --dataset_config_name wikitext-2-raw-v1 --do_train \
--output_dir /tmp/test-clm --per_device_train_batch_size 4 --max_steps 200
{'train_runtime': 101.9003, 'train_samples_per_second': 1.963, 'epoch': 0.69}
DDP w/o NVLink
