1.数据加载
train_loader = build_dataloader( train_dataset, cfg.data.imgs_per_gpu, cfg.data.workers_per_gpu, dist=distributed)中加载data，文件来源/home/zz/SA-SSD-master/mmdet/datasets/loader/build_loader.py中产生batch_size
// An highlighted block batch_size = num_gpus * imgs_per_gpu num_workers = num_gpus * workers_per_gpu