Simplifying EMA...

Author: rwightman

timm/utils/model.py

@@ -6,10 +6,7 @@
 
 
 def unwrap_model(model):
-    if isinstance(model, ModelEma):
-        return unwrap_model(model.ema)
-    else:
-        return model.module if hasattr(model, 'module') else model
+    return model.module if hasattr(model, 'module') else model
 
 
 def get_state_dict(model, unwrap_fn=unwrap_model):

timm/utils/model_ema.py

@@ -2,16 +2,13 @@
 
 Hacked together by / Copyright 2020 Ross Wightman
 """
-import logging
-from collections import OrderedDict
 from copy import deepcopy
 
 import torch
+import torch.nn as nn
 
-_logger = logging.getLogger(__name__)
 
-
-class ModelEma:
+class ModelEma(nn.Module):
     """ Model Exponential Moving Average
     Keep a moving average of everything in the model state_dict (parameters and buffers).
 
@@ -32,46 +29,20 @@ class ModelEma:
     GPU assignment and distributed training wrappers.
     I've tested with the sequence in my own train.py for torch.DataParallel, apex.DDP, and single-GPU.
     """
-    def __init__(self, model, decay=0.9999, device='', resume=''):
+    def __init__(self, model, decay=0.9999, device=None):
+        super(ModelEma, self).__init__()
         # make a copy of the model for accumulating moving average of weights
-        self.ema = deepcopy(model)
-        self.ema.eval()
+        self.module = deepcopy(model)
+        self.module.eval()
         self.decay = decay
         self.device = device  # perform ema on different device from model if set
-        if device:
-            self.ema.to(device=device)
-        self.ema_has_module = hasattr(self.ema, 'module')
-        if resume:
-            self._load_checkpoint(resume)
-        for p in self.ema.parameters():
-            p.requires_grad_(False)
-
-    def _load_checkpoint(self, checkpoint_path):
-        checkpoint = torch.load(checkpoint_path, map_location='cpu')
-        assert isinstance(checkpoint, dict)
-        if 'state_dict_ema' in checkpoint:
-            new_state_dict = OrderedDict()
-            for k, v in checkpoint['state_dict_ema'].items():
-                # ema model may have been wrapped by DataParallel, and need module prefix
-                if self.ema_has_module:
-                    name = 'module.' + k if not k.startswith('module') else k
-                else:
-                    name = k
-                new_state_dict[name] = v
-            self.ema.load_state_dict(new_state_dict)
-            _logger.info("Loaded state_dict_ema")
-        else:
-            _logger.warning("Failed to find state_dict_ema, starting from loaded model weights")
+        if device is not None:
+            self.module.to(device=device)
 
     def update(self, model):
-        # correct a mismatch in state dict keys
-        needs_module = hasattr(model, 'module') and not self.ema_has_module
         with torch.no_grad():
-            msd = model.state_dict()
-            for k, ema_v in self.ema.state_dict().items():
-                if needs_module:
-                    k = 'module.' + k
-                model_v = msd[k].detach()
+            for ema_v, model_v in zip(self.module.state_dict().values(), model.state_dict().values()):
+                assert ema_v.shape == model_v.shape
                 if self.device:
                     model_v = model_v.to(device=self.device)
                 ema_v.copy_(ema_v * self.decay + (1. - self.decay) * model_v)

train.py

@@ -568,7 +568,7 @@ def main():
                 if args.distributed and args.dist_bn in ('broadcast', 'reduce'):
                     distribute_bn(model_ema, args.world_size, args.dist_bn == 'reduce')
                 ema_eval_metrics = validate(
-                    model_ema.ema, loader_eval, validate_loss_fn, args, amp_autocast=amp_autocast, log_suffix=' (EMA)')
+                    model_ema.module, loader_eval, validate_loss_fn, args, amp_autocast=amp_autocast, log_suffix=' (EMA)')
                 eval_metrics = ema_eval_metrics
 
             if lr_scheduler is not None: