Eliminate total_batch_size variable (ultralytics#3697)

* Eliminate `total_batch_size` variable

* cleanup

* Update train.py

train.py

@@ -46,10 +46,11 @@ def train(hyp,  # path/to/hyp.yaml or hyp dictionary
           opt,
           device,
           ):
-    save_dir, epochs, batch_size, total_batch_size, weights, single_cls = \
-        Path(opt.save_dir), opt.epochs, opt.batch_size, opt.total_batch_size, opt.weights, opt.single_cls
+    save_dir, epochs, batch_size, weights, single_cls = \
+        opt.save_dir, opt.epochs, opt.batch_size, opt.weights, opt.single_cls
 
     # Directories
+    save_dir = Path(save_dir)
     wdir = save_dir / 'weights'
     wdir.mkdir(parents=True, exist_ok=True)  # make dir
     last = wdir / 'last.pt'
@@ -127,8 +128,8 @@ def train(hyp,  # path/to/hyp.yaml or hyp dictionary
 
     # Optimizer
     nbs = 64  # nominal batch size
-    accumulate = max(round(nbs / total_batch_size), 1)  # accumulate loss before optimizing
-    hyp['weight_decay'] *= total_batch_size * accumulate / nbs  # scale weight_decay
+    accumulate = max(round(nbs / batch_size), 1)  # accumulate loss before optimizing
+    hyp['weight_decay'] *= batch_size * accumulate / nbs  # scale weight_decay
     logger.info(f"Scaled weight_decay = {hyp['weight_decay']}")
 
     pg0, pg1, pg2 = [], [], []  # optimizer parameter groups
@@ -205,7 +206,7 @@ def train(hyp,  # path/to/hyp.yaml or hyp dictionary
         logger.info('Using SyncBatchNorm()')
 
     # Trainloader
-    dataloader, dataset = create_dataloader(train_path, imgsz, batch_size, gs, single_cls,
+    dataloader, dataset = create_dataloader(train_path, imgsz, batch_size // WORLD_SIZE, gs, single_cls,
                                             hyp=hyp, augment=True, cache=opt.cache_images, rect=opt.rect, rank=RANK,
                                             workers=opt.workers,
                                             image_weights=opt.image_weights, quad=opt.quad, prefix=colorstr('train: '))
@@ -215,7 +216,7 @@ def train(hyp,  # path/to/hyp.yaml or hyp dictionary
 
     # Process 0
     if RANK in [-1, 0]:
-        testloader = create_dataloader(test_path, imgsz_test, batch_size * 2, gs, single_cls,
+        testloader = create_dataloader(test_path, imgsz_test, batch_size // WORLD_SIZE * 2, gs, single_cls,
                                        hyp=hyp, cache=opt.cache_images and not opt.notest, rect=True, rank=-1,
                                        workers=opt.workers,
                                        pad=0.5, prefix=colorstr('val: '))[0]
@@ -302,7 +303,7 @@ def train(hyp,  # path/to/hyp.yaml or hyp dictionary
             if ni <= nw:
                 xi = [0, nw]  # x interp
                 # model.gr = np.interp(ni, xi, [0.0, 1.0])  # iou loss ratio (obj_loss = 1.0 or iou)
-                accumulate = max(1, np.interp(ni, xi, [1, nbs / total_batch_size]).round())
+                accumulate = max(1, np.interp(ni, xi, [1, nbs / batch_size]).round())
                 for j, x in enumerate(optimizer.param_groups):
                     # bias lr falls from 0.1 to lr0, all other lrs rise from 0.0 to lr0
                     x['lr'] = np.interp(ni, xi, [hyp['warmup_bias_lr'] if j == 2 else 0.0, x['initial_lr'] * lf(epoch)])
@@ -371,7 +372,7 @@ def train(hyp,  # path/to/hyp.yaml or hyp dictionary
             if not opt.notest or final_epoch:  # Calculate mAP
                 wandb_logger.current_epoch = epoch + 1
                 results, maps, _ = test.test(data_dict,
-                                             batch_size=batch_size * 2,
+                                             batch_size=batch_size // WORLD_SIZE * 2,
                                              imgsz=imgsz_test,
                                              model=ema.ema,
                                              single_cls=single_cls,
@@ -439,7 +440,7 @@ def train(hyp,  # path/to/hyp.yaml or hyp dictionary
             if is_coco:  # COCO dataset
                 for m in [last, best] if best.exists() else [last]:  # speed, mAP tests
                     results, _, _ = test.test(opt.data,
-                                              batch_size=batch_size * 2,
+                                              batch_size=batch_size // WORLD_SIZE * 2,
                                               imgsz=imgsz_test,
                                               conf_thres=0.001,
                                               iou_thres=0.7,
@@ -518,7 +519,7 @@ def main(opt):
         assert os.path.isfile(ckpt), 'ERROR: --resume checkpoint does not exist'
         with open(Path(ckpt).parent.parent / 'opt.yaml') as f:
             opt = argparse.Namespace(**yaml.safe_load(f))  # replace
-        opt.cfg, opt.weights, opt.resume, opt.batch_size = '', ckpt, True, opt.total_batch_size  # reinstate
+        opt.cfg, opt.weights, opt.resume = '', ckpt, True  # reinstate
         logger.info('Resuming training from %s' % ckpt)
     else:
         # opt.hyp = opt.hyp or ('hyp.finetune.yaml' if opt.weights else 'hyp.scratch.yaml')
@@ -529,17 +530,15 @@ def main(opt):
         opt.save_dir = str(increment_path(Path(opt.project) / opt.name, exist_ok=opt.exist_ok | opt.evolve))
 
     # DDP mode
-    opt.total_batch_size = opt.batch_size
     device = select_device(opt.device, batch_size=opt.batch_size)
     if LOCAL_RANK != -1:
         from datetime import timedelta
-        assert torch.cuda.device_count() > LOCAL_RANK, 'too few GPUS for DDP command'
+        assert torch.cuda.device_count() > LOCAL_RANK, 'insufficient CUDA devices for DDP command'
         torch.cuda.set_device(LOCAL_RANK)
         device = torch.device('cuda', LOCAL_RANK)
         dist.init_process_group(backend="gloo", timeout=timedelta(seconds=60))
         assert opt.batch_size % WORLD_SIZE == 0, '--batch-size must be multiple of CUDA device count'
         assert not opt.image_weights, '--image-weights argument is not compatible with DDP training'
-        opt.batch_size = opt.total_batch_size // WORLD_SIZE
 
     # Train
     if not opt.evolve: