How to use multi-GPU to train our model with the newest stable version. Just cast the model to nn.DataParallel? Or plus manually converting BN to nn.SyncBatchNorm?
        model = nn.DataParallel(model)
        model = nn.SyncBatchNorm.convert_sync_batchnorm(model) (Is this necessary?)

Moreover, do we need to set the batch-size to nGPUs times the single GPU batch-size?