Reduce variance of classification references evaluation (#4609)

references/classification/train.py

 import datetime
 import os
 import time
+import warnings
 
 import presets
 import torch
@@ -54,6 +55,8 @@ def evaluate(model, criterion, data_loader, device, print_freq=100, log_suffix="
     model.eval()
     metric_logger = utils.MetricLogger(delimiter="  ")
     header = f"Test: {log_suffix}"
+
+    num_processed_samples = 0
     with torch.no_grad():
         for image, target in metric_logger.log_every(data_loader, print_freq, header):
             image = image.to(device, non_blocking=True)
@@ -68,7 +71,23 @@ def evaluate(model, criterion, data_loader, device, print_freq=100, log_suffix="
             metric_logger.update(loss=loss.item())
             metric_logger.meters["acc1"].update(acc1.item(), n=batch_size)
             metric_logger.meters["acc5"].update(acc5.item(), n=batch_size)
+            num_processed_samples += batch_size
     # gather the stats from all processes
+
+    num_processed_samples = utils.reduce_across_processes(num_processed_samples)
+    if (
+        hasattr(data_loader.dataset, "__len__")
+        and len(data_loader.dataset) != num_processed_samples
+        and torch.distributed.get_rank() == 0
+    ):
+        # See FIXME above
+        warnings.warn(
+            f"It looks like the dataset has {len(data_loader.dataset)} samples, but {num_processed_samples} "
+            "samples were used for the validation, which might bias the results. "
+            "Try adjusting the batch size and / or the world size. "
+            "Setting the world size to 1 is always a safe bet."
+        )
+
     metric_logger.synchronize_between_processes()
 
     print(f"{header} Acc@1 {metric_logger.acc1.global_avg:.3f} Acc@5 {metric_logger.acc5.global_avg:.3f}")
@@ -147,7 +166,7 @@ def load_data(traindir, valdir, args):
     print("Creating data loaders")
     if args.distributed:
         train_sampler = torch.utils.data.distributed.DistributedSampler(dataset)
-        test_sampler = torch.utils.data.distributed.DistributedSampler(dataset_test)
+        test_sampler = torch.utils.data.distributed.DistributedSampler(dataset_test, shuffle=False)
     else:
         train_sampler = torch.utils.data.RandomSampler(dataset)
         test_sampler = torch.utils.data.SequentialSampler(dataset_test)
@@ -164,7 +183,11 @@ def main(args):
 
     device = torch.device(args.device)
 
-    torch.backends.cudnn.benchmark = True
+    if args.use_deterministic_algorithms:
+        torch.backends.cudnn.benchmark = False
+        torch.use_deterministic_algorithms(True)
+    else:
+        torch.backends.cudnn.benchmark = True
 
     train_dir = os.path.join(args.data_path, "train")
     val_dir = os.path.join(args.data_path, "val")
@@ -277,6 +300,10 @@ def main(args):
             model_ema.load_state_dict(checkpoint["model_ema"])
 
     if args.test_only:
+        # We disable the cudnn benchmarking because it can noticeably affect the accuracy
+        torch.backends.cudnn.benchmark = False
+        torch.backends.cudnn.deterministic = True
+
         evaluate(model, criterion, data_loader_test, device=device)
         return
 
@@ -394,6 +421,9 @@ def get_args_parser(add_help=True):
         default=0.9,
         help="decay factor for Exponential Moving Average of model parameters(default: 0.9)",
     )
+    parser.add_argument(
+        "--use-deterministic-algorithms", action="store_true", help="Forces the use of deterministic algorithms only."
+    )
 
     return parser
 

references/classification/utils.py

@@ -32,11 +32,7 @@ class SmoothedValue(object):
         """
         Warning: does not synchronize the deque!
         """
-        if not is_dist_avail_and_initialized():
-            return
-        t = torch.tensor([self.count, self.total], dtype=torch.float64, device="cuda")
-        dist.barrier()
-        dist.all_reduce(t)
+        t = reduce_across_processes([self.count, self.total])
         t = t.tolist()
         self.count = int(t[0])
         self.total = t[1]
@@ -400,3 +396,12 @@ def store_model_weights(model, checkpoint_path, checkpoint_key="model", strict=T
     os.replace(tmp_path, output_path)
 
     return output_path
+
+
+def reduce_across_processes(val):
+    if not is_dist_avail_and_initialized():
+        return val
+    t = torch.tensor(val, device="cuda")
+    dist.barrier()
+    dist.all_reduce(t)
+    return t