generator seed fix for DDP mAP drop (#9545)

* Try to fix DDP mAP drop by setting generator's seed to RANK

* Fix default activation bug

* Update dataloaders.py

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Update dataloaders.py

Co-authored-by: Glenn Jocher <glenn.jocher@ultralytics.com>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

utils/dataloaders.py

@@ -40,6 +40,7 @@ IMG_FORMATS = 'bmp', 'dng', 'jpeg', 'jpg', 'mpo', 'png', 'tif', 'tiff', 'webp',
 VID_FORMATS = 'asf', 'avi', 'gif', 'm4v', 'mkv', 'mov', 'mp4', 'mpeg', 'mpg', 'ts', 'wmv'  # include video suffixes
 BAR_FORMAT = '{l_bar}{bar:10}{r_bar}{bar:-10b}'  # tqdm bar format
 LOCAL_RANK = int(os.getenv('LOCAL_RANK', -1))  # https://pytorch.org/docs/stable/elastic/run.html
+RANK = int(os.getenv('RANK', -1))
 PIN_MEMORY = str(os.getenv('PIN_MEMORY', True)).lower() == 'true'  # global pin_memory for dataloaders
 
 # Get orientation exif tag
@@ -139,7 +140,7 @@ def create_dataloader(path,
     sampler = None if rank == -1 else distributed.DistributedSampler(dataset, shuffle=shuffle)
     loader = DataLoader if image_weights else InfiniteDataLoader  # only DataLoader allows for attribute updates
     generator = torch.Generator()
-    generator.manual_seed(0)
+    generator.manual_seed(6148914691236517205 + RANK)
     return loader(dataset,
                   batch_size=batch_size,
                   shuffle=shuffle and sampler is None,
@@ -1169,7 +1170,7 @@ def create_classification_dataloader(path,
     nw = min([os.cpu_count() // max(nd, 1), batch_size if batch_size > 1 else 0, workers])
     sampler = None if rank == -1 else distributed.DistributedSampler(dataset, shuffle=shuffle)
     generator = torch.Generator()
-    generator.manual_seed(0)
+    generator.manual_seed(6148914691236517205 + RANK)
     return InfiniteDataLoader(dataset,
                               batch_size=batch_size,
                               shuffle=shuffle and sampler is None,