change to apex for better fp16 and multi-gpu support

README.md

@@ -326,7 +326,7 @@ The optimizer accepts the following arguments:
 - `b1` : Adams b1. Default : `0.9`
 - `b2` : Adams b2. Default : `0.999`
 - `e` : Adams epsilon. Default : `1e-6`
-- `weight_decay_rate:` Weight decay. Default : `0.01`
+- `weight_decay:` Weight decay. Default : `0.01`
 - `max_grad_norm` : Maximum norm for the gradients (`-1` means no clipping). Default : `1.0`
 
 ## Examples

examples/run_classifier.py

 # coding=utf-8
 # Copyright 2018 The Google AI Language Team Authors and The HugginFace Inc. team.
+# Copyright (c) 2018, NVIDIA CORPORATION.  All rights reserved.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -35,6 +36,13 @@ from pytorch_pretrained_bert.modeling import BertForSequenceClassification
 from pytorch_pretrained_bert.optimization import BertAdam
 from pytorch_pretrained_bert.file_utils import PYTORCH_PRETRAINED_BERT_CACHE
 
+try:
+    from apex.optimizers import FP16_Optimizer
+    from apex.optimizers import FusedAdam
+    from apex.parallel import DistributedDataParallel as DDP
+except ImportError:
+    raise ImportError("Please install apex from https://www.github.com/nvidia/apex to run this.")
+
 logging.basicConfig(format = '%(asctime)s - %(levelname)s - %(name)s -   %(message)s',
                     datefmt = '%m/%d/%Y %H:%M:%S',
                     level = logging.INFO)
@@ -295,34 +303,10 @@ def accuracy(out, labels):
     outputs = np.argmax(out, axis=1)
     return np.sum(outputs == labels)
 
-def copy_optimizer_params_to_model(named_params_model, named_params_optimizer):
-    """ Utility function for optimize_on_cpu and 16-bits training.
-        Copy the parameters optimized on CPU/RAM back to the model on GPU
-    """
-    for (name_opti, param_opti), (name_model, param_model) in zip(named_params_optimizer, named_params_model):
-        if name_opti != name_model:
-            logger.error("name_opti != name_model: {} {}".format(name_opti, name_model))
-            raise ValueError
-        param_model.data.copy_(param_opti.data)
-
-def set_optimizer_params_grad(named_params_optimizer, named_params_model, test_nan=False):
-    """ Utility function for optimize_on_cpu and 16-bits training.
-        Copy the gradient of the GPU parameters to the CPU/RAMM copy of the model
-    """
-    is_nan = False
-    for (name_opti, param_opti), (name_model, param_model) in zip(named_params_optimizer, named_params_model):
-        if name_opti != name_model:
-            logger.error("name_opti != name_model: {} {}".format(name_opti, name_model))
-            raise ValueError
-        if param_model.grad is not None:
-            if test_nan and torch.isnan(param_model.grad).sum() > 0:
-                is_nan = True
-            if param_opti.grad is None:
-                param_opti.grad = torch.nn.Parameter(param_opti.data.new().resize_(*param_opti.data.size()))
-            param_opti.grad.data.copy_(param_model.grad.data)
-        else:
-            param_opti.grad = None
-    return is_nan
+def warmup_linear(x, warmup=0.002):
+    if x < warmup:
+        return x/warmup
+    return 1.0 - x
 
 def main():
     parser = argparse.ArgumentParser()
@@ -403,17 +387,15 @@ def main():
                         type=int,
                         default=1,
                         help="Number of updates steps to accumulate before performing a backward/update pass.")
-    parser.add_argument('--optimize_on_cpu',
-                        default=False,
-                        action='store_true',
-                        help="Whether to perform optimization and keep the optimizer averages on CPU")
     parser.add_argument('--fp16',
                         default=False,
                         action='store_true',
                         help="Whether to use 16-bit float precision instead of 32-bit")
     parser.add_argument('--loss_scale',
-                        type=float, default=128,
-                        help='Loss scaling, positive power of 2 values can improve fp16 convergence.')
+                        type=float, default=0,
+                        help="Loss scaling to improve fp16 numeric stability. Only used when fp16 set to True.\n"
+                             "0 (default value): dynamic loss scaling.\n"
+                             "Positive power of 2: static loss scaling value.\n")
 
     args = parser.parse_args()
 
@@ -433,13 +415,11 @@ def main():
         device = torch.device("cuda" if torch.cuda.is_available() and not args.no_cuda else "cpu")
         n_gpu = torch.cuda.device_count()
     else:
+        torch.cuda.set_device(args.local_rank)
         device = torch.device("cuda", args.local_rank)
         n_gpu = 1
         # Initializes the distributed backend which will take care of sychronizing nodes/GPUs
         torch.distributed.init_process_group(backend='nccl')
-        if args.fp16:
-            logger.info("16-bits training currently not supported in distributed training")
-            args.fp16 = False # (see https://github.com/pytorch/pytorch/pull/13496)
     logger.info("device %s n_gpu %d distributed training %r", device, n_gpu, bool(args.local_rank != -1))
 
     if args.gradient_accumulation_steps < 1:
@@ -487,28 +467,31 @@ def main():
         model.half()
     model.to(device)
     if args.local_rank != -1:
-        model = torch.nn.parallel.DistributedDataParallel(model, device_ids=[args.local_rank],
-                                                          output_device=args.local_rank)
+        model = DDP(model)
     elif n_gpu > 1:
         model = torch.nn.DataParallel(model)
 
     # Prepare optimizer
-    if args.fp16:
-        param_optimizer = [(n, param.clone().detach().to('cpu').float().requires_grad_()) \
-                            for n, param in model.named_parameters()]
-    elif args.optimize_on_cpu:
-        param_optimizer = [(n, param.clone().detach().to('cpu').requires_grad_()) \
-                            for n, param in model.named_parameters()]
-    else:
     param_optimizer = list(model.named_parameters())
-    no_decay = ['bias', 'gamma', 'beta']
+    no_decay = ['bias', 'LayerNorm.bias', 'LayerNorm.weight']
     optimizer_grouped_parameters = [
-        {'params': [p for n, p in param_optimizer if not any(nd in n for nd in no_decay)], 'weight_decay_rate': 0.01},
-        {'params': [p for n, p in param_optimizer if any(nd in n for nd in no_decay)], 'weight_decay_rate': 0.0}
+        {'params': [p for n, p in param_optimizer if not any(nd in n for nd in no_decay)], 'weight_decay': 0.01},
+        {'params': [p for n, p in param_optimizer if any(nd in n for nd in no_decay)], 'weight_decay': 0.0}
         ]
     t_total = num_train_steps
     if args.local_rank != -1:
         t_total = t_total // torch.distributed.get_world_size()
+    if args.fp16:
+        optimizer = FusedAdam(optimizer_grouped_parameters,
+                              lr=args.learning_rate,
+                              bias_correction=False,
+                              max_grad_norm=1.0)
+        if args.loss_scale == 0:
+            optimizer = FP16_Optimizer(optimizer, dynamic_loss_scale=True)
+        else:
+            optimizer = FP16_Optimizer(optimizer, static_loss_scale=args.loss_scale)
+
+    else:
         optimizer = BertAdam(optimizer_grouped_parameters,
                              lr=args.learning_rate,
                              warmup=args.warmup_proportion,
@@ -543,34 +526,24 @@ def main():
                 loss = model(input_ids, segment_ids, input_mask, label_ids)
                 if n_gpu > 1:
                     loss = loss.mean() # mean() to average on multi-gpu.
-                if args.fp16 and args.loss_scale != 1.0:
-                    # rescale loss for fp16 training
-                    # see https://docs.nvidia.com/deeplearning/sdk/mixed-precision-training/index.html
-                    loss = loss * args.loss_scale
                 if args.gradient_accumulation_steps > 1:
                     loss = loss / args.gradient_accumulation_steps
+
+                if args.fp16:
+                    optimizer.backward(loss)
+                else:
                     loss.backward()
+
                 tr_loss += loss.item()
                 nb_tr_examples += input_ids.size(0)
                 nb_tr_steps += 1
                 if (step + 1) % args.gradient_accumulation_steps == 0:
-                    if args.fp16 or args.optimize_on_cpu:
-                        if args.fp16 and args.loss_scale != 1.0:
-                            # scale down gradients for fp16 training
-                            for param in model.parameters():
-                                if param.grad is not None:
-                                    param.grad.data = param.grad.data / args.loss_scale
-                        is_nan = set_optimizer_params_grad(param_optimizer, model.named_parameters(), test_nan=True)
-                        if is_nan:
-                            logger.info("FP16 TRAINING: Nan in gradients, reducing loss scaling")
-                            args.loss_scale = args.loss_scale / 2
-                            model.zero_grad()
-                            continue
-                        optimizer.step()
-                        copy_optimizer_params_to_model(model.named_parameters(), param_optimizer)
-                    else:
+                    # modify learning rate with special warm up BERT uses
+                    lr_this_step = args.learning_rate * warmup_linear(global_step/t_total, args.warmup_proportion)
+                    for param_group in optimizer.param_groups:
+                        param_group['lr'] = lr_this_step
                     optimizer.step()
-                    model.zero_grad()
+                    optimizer.zero_grad()
                     global_step += 1
 
     if args.do_eval and (args.local_rank == -1 or torch.distributed.get_rank() == 0):

examples/run_squad.py

 # coding=utf-8
 # Copyright 2018 The Google AI Language Team Authors and The HugginFace Inc. team.
+# Copyright (c) 2018, NVIDIA CORPORATION.  All rights reserved.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -38,6 +39,13 @@ from pytorch_pretrained_bert.modeling import BertForQuestionAnswering
 from pytorch_pretrained_bert.optimization import BertAdam
 from pytorch_pretrained_bert.file_utils import PYTORCH_PRETRAINED_BERT_CACHE
 
+try:
+    from apex.optimizers import FP16_Optimizer
+    from apex.optimizers import FusedAdam
+    from apex.parallel import DistributedDataParallel as DDP
+except ImportError:
+    raise ImportError("Please install apex from https://www.github.com/nvidia/apex to run this.")
+
 logging.basicConfig(format = '%(asctime)s - %(levelname)s - %(name)s -   %(message)s',
                     datefmt = '%m/%d/%Y %H:%M:%S',
                     level = logging.INFO)
@@ -669,34 +677,10 @@ def _compute_softmax(scores):
         probs.append(score / total_sum)
     return probs
 
-def copy_optimizer_params_to_model(named_params_model, named_params_optimizer):
-    """ Utility function for optimize_on_cpu and 16-bits training.
-        Copy the parameters optimized on CPU/RAM back to the model on GPU
-    """
-    for (name_opti, param_opti), (name_model, param_model) in zip(named_params_optimizer, named_params_model):
-        if name_opti != name_model:
-            logger.error("name_opti != name_model: {} {}".format(name_opti, name_model))
-            raise ValueError
-        param_model.data.copy_(param_opti.data)
-
-def set_optimizer_params_grad(named_params_optimizer, named_params_model, test_nan=False):
-    """ Utility function for optimize_on_cpu and 16-bits training.
-        Copy the gradient of the GPU parameters to the CPU/RAMM copy of the model
-    """
-    is_nan = False
-    for (name_opti, param_opti), (name_model, param_model) in zip(named_params_optimizer, named_params_model):
-        if name_opti != name_model:
-            logger.error("name_opti != name_model: {} {}".format(name_opti, name_model))
-            raise ValueError
-        if param_model.grad is not None:
-            if test_nan and torch.isnan(param_model.grad).sum() > 0:
-                is_nan = True
-            if param_opti.grad is None:
-                param_opti.grad = torch.nn.Parameter(param_opti.data.new().resize_(*param_opti.data.size()))
-            param_opti.grad.data.copy_(param_model.grad.data)
-        else:
-            param_opti.grad = None
-    return is_nan
+def warmup_linear(x, warmup=0.002):
+    if x < warmup:
+        return x/warmup
+    return 1.0 - x
 
 def main():
     parser = argparse.ArgumentParser()
@@ -759,17 +743,15 @@ def main():
                         type=int,
                         default=-1,
                         help="local_rank for distributed training on gpus")
-    parser.add_argument('--optimize_on_cpu',
-                        default=False,
-                        action='store_true',
-                        help="Whether to perform optimization and keep the optimizer averages on CPU")
     parser.add_argument('--fp16',
                         default=False,
                         action='store_true',
                         help="Whether to use 16-bit float precision instead of 32-bit")
     parser.add_argument('--loss_scale',
-                        type=float, default=128,
-                        help='Loss scaling, positive power of 2 values can improve fp16 convergence.')
+                        type=float, default=0,
+                        help="Loss scaling to improve fp16 numeric stability. Only used when fp16 set to True.\n"
+                             "0 (default value): dynamic loss scaling.\n"
+                             "Positive power of 2: static loss scaling value.\n")
 
     args = parser.parse_args()
 
@@ -777,13 +759,11 @@ def main():
         device = torch.device("cuda" if torch.cuda.is_available() and not args.no_cuda else "cpu")
         n_gpu = torch.cuda.device_count()
     else:
+        torch.cuda.set_device(args.local_rank)
         device = torch.device("cuda", args.local_rank)
         n_gpu = 1
         # Initializes the distributed backend which will take care of sychronizing nodes/GPUs
         torch.distributed.init_process_group(backend='nccl')
-        if args.fp16:
-            logger.info("16-bits training currently not supported in distributed training")
-            args.fp16 = False # (see https://github.com/pytorch/pytorch/pull/13496)
     logger.info("device: {} n_gpu: {}, distributed training: {}, 16-bits trainiing: {}".format(
         device, n_gpu, bool(args.local_rank != -1), args.fp16))
 
@@ -828,32 +808,41 @@ def main():
     # Prepare model
     model = BertForQuestionAnswering.from_pretrained(args.bert_model,
                 cache_dir=PYTORCH_PRETRAINED_BERT_CACHE / 'distributed_{}'.format(args.local_rank))
+
     if args.fp16:
         model.half()
     model.to(device)
     if args.local_rank != -1:
-        model = torch.nn.parallel.DistributedDataParallel(model, device_ids=[args.local_rank],
-                                                          output_device=args.local_rank)
+        model = DDP(model)
     elif n_gpu > 1:
         model = torch.nn.DataParallel(model)
 
     # Prepare optimizer
-    if args.fp16:
-        param_optimizer = [(n, param.clone().detach().to('cpu').float().requires_grad_()) \
-                            for n, param in model.named_parameters()]
-    elif args.optimize_on_cpu:
-        param_optimizer = [(n, param.clone().detach().to('cpu').requires_grad_()) \
-                            for n, param in model.named_parameters()]
-    else:
     param_optimizer = list(model.named_parameters())
-    no_decay = ['bias', 'gamma', 'beta']
+
+    # hack to remove pooler, which is not used
+    # thus it produce None grad that break apex
+    param_optimizer = [n for n in param_optimizer if 'pooler' not in n[0]]
+
+    no_decay = ['bias', 'LayerNorm.bias', 'LayerNorm.weight']
     optimizer_grouped_parameters = [
-        {'params': [p for n, p in param_optimizer if not any(nd in n for nd in no_decay)], 'weight_decay_rate': 0.01},
-        {'params': [p for n, p in param_optimizer if any(nd in n for nd in no_decay)], 'weight_decay_rate': 0.0}
+        {'params': [p for n, p in param_optimizer if not any(nd in n for nd in no_decay)], 'weight_decay': 0.01},
+        {'params': [p for n, p in param_optimizer if any(nd in n for nd in no_decay)], 'weight_decay': 0.0}
         ]
+
     t_total = num_train_steps
     if args.local_rank != -1:
         t_total = t_total // torch.distributed.get_world_size()
+    if args.fp16:
+        optimizer = FusedAdam(optimizer_grouped_parameters,
+                              lr=args.learning_rate,
+                              bias_correction=False,
+                              max_grad_norm=1.0)
+        if args.loss_scale == 0:
+            optimizer = FP16_Optimizer(optimizer, dynamic_loss_scale=True)
+        else:
+            optimizer = FP16_Optimizer(optimizer, static_loss_scale=args.loss_scale)
+    else:
         optimizer = BertAdam(optimizer_grouped_parameters,
                              lr=args.learning_rate,
                              warmup=args.warmup_proportion,
@@ -906,31 +895,20 @@ def main():
                 loss = model(input_ids, segment_ids, input_mask, start_positions, end_positions)
                 if n_gpu > 1:
                     loss = loss.mean() # mean() to average on multi-gpu.
-                if args.fp16 and args.loss_scale != 1.0:
-                    # rescale loss for fp16 training
-                    # see https://docs.nvidia.com/deeplearning/sdk/mixed-precision-training/index.html
-                    loss = loss * args.loss_scale
                 if args.gradient_accumulation_steps > 1:
                     loss = loss / args.gradient_accumulation_steps
+
+                if args.fp16:
+                    optimizer.backward(loss)
+                else:
                     loss.backward()
                 if (step + 1) % args.gradient_accumulation_steps == 0:
-                    if args.fp16 or args.optimize_on_cpu:
-                        if args.fp16 and args.loss_scale != 1.0:
-                            # scale down gradients for fp16 training
-                            for param in model.parameters():
-                                if param.grad is not None:
-                                    param.grad.data = param.grad.data / args.loss_scale
-                        is_nan = set_optimizer_params_grad(param_optimizer, model.named_parameters(), test_nan=True)
-                        if is_nan:
-                            logger.info("FP16 TRAINING: Nan in gradients, reducing loss scaling")
-                            args.loss_scale = args.loss_scale / 2
-                            model.zero_grad()
-                            continue
-                        optimizer.step()
-                        copy_optimizer_params_to_model(model.named_parameters(), param_optimizer)
-                    else:
+                    # modify learning rate with special warm up BERT uses
+                    lr_this_step = args.learning_rate * warmup_linear(global_step/t_total, args.warmup_proportion)
+                    for param_group in optimizer.param_groups:
+                        param_group['lr'] = lr_this_step
                     optimizer.step()
-                    model.zero_grad()
+                    optimizer.zero_grad()
                     global_step += 1
 
     if args.do_predict and (args.local_rank == -1 or torch.distributed.get_rank() == 0):

pytorch_pretrained_bert/modeling.py

 # coding=utf-8
 # Copyright 2018 The Google AI Language Team Authors and The HugginFace Inc. team.
+# Copyright (c) 2018, NVIDIA CORPORATION.  All rights reserved.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -30,6 +31,10 @@ import shutil
 import torch
 from torch import nn
 from torch.nn import CrossEntropyLoss
+try:
+    from apex.normalization.fused_layer_norm import FusedLayerNorm
+except ImportError:
+    raise ImportError("Please install apex from https://www.github.com/nvidia/apex to run this.")
 
 from .file_utils import cached_path
 
@@ -180,7 +185,7 @@ class BertEmbeddings(nn.Module):
 
         # self.LayerNorm is not snake-cased to stick with TensorFlow model variable name and be able to load
         # any TensorFlow checkpoint file
-        self.LayerNorm = BertLayerNorm(config)
+        self.LayerNorm = FusedLayerNorm(config.hidden_size, eps=1e-12)
         self.dropout = nn.Dropout(config.hidden_dropout_prob)
 
     def forward(self, input_ids, token_type_ids=None):
@@ -255,7 +260,7 @@ class BertSelfOutput(nn.Module):
     def __init__(self, config):
         super(BertSelfOutput, self).__init__()
         self.dense = nn.Linear(config.hidden_size, config.hidden_size)
-        self.LayerNorm = BertLayerNorm(config)
+        self.LayerNorm = FusedLayerNorm(config.hidden_size, eps=1e-12)
         self.dropout = nn.Dropout(config.hidden_dropout_prob)
 
     def forward(self, hidden_states, input_tensor):
@@ -294,7 +299,7 @@ class BertOutput(nn.Module):
     def __init__(self, config):
         super(BertOutput, self).__init__()
         self.dense = nn.Linear(config.intermediate_size, config.hidden_size)
-        self.LayerNorm = BertLayerNorm(config)
+        self.LayerNorm = FusedLayerNorm(config.hidden_size, eps=1e-12)
         self.dropout = nn.Dropout(config.hidden_dropout_prob)
 
     def forward(self, hidden_states, input_tensor):
@@ -356,7 +361,7 @@ class BertPredictionHeadTransform(nn.Module):
         self.dense = nn.Linear(config.hidden_size, config.hidden_size)
         self.transform_act_fn = ACT2FN[config.hidden_act] \
             if isinstance(config.hidden_act, str) else config.hidden_act
-        self.LayerNorm = BertLayerNorm(config)
+        self.LayerNorm = FusedLayerNorm(config.hidden_size, eps=1e-12)
 
     def forward(self, hidden_states):
         hidden_states = self.dense(hidden_states)
@@ -438,6 +443,9 @@ class PreTrainedBertModel(nn.Module):
             # Slightly different from the TF version which uses truncated_normal for initialization
             # cf https://github.com/pytorch/pytorch/pull/5617
             module.weight.data.normal_(mean=0.0, std=self.config.initializer_range)
+        elif isinstance(module, FusedLayerNorm):
+            module.bias.data.normal_(mean=0.0, std=self.config.initializer_range)
+            module.weight.data.normal_(mean=0.0, std=self.config.initializer_range)
         elif isinstance(module, BertLayerNorm):
             module.beta.data.normal_(mean=0.0, std=self.config.initializer_range)
             module.gamma.data.normal_(mean=0.0, std=self.config.initializer_range)
@@ -505,6 +513,20 @@ class PreTrainedBertModel(nn.Module):
         weights_path = os.path.join(serialization_dir, WEIGHTS_NAME)
         state_dict = torch.load(weights_path)
 
+        old_keys = []
+        new_keys = []
+        for key in state_dict.keys():
+            new_key = None
+            if 'gamma' in key:
+                new_key = key.replace('gamma','weight')
+            if 'beta' in key:
+                new_key = key.replace('beta','bias')
+            if new_key:
+                old_keys.append(key)
+                new_keys.append(new_key)
+        for old_key, new_key in zip(old_keys, new_keys):
+            state_dict[new_key]=state_dict.pop(old_key)
+
         missing_keys = []
         unexpected_keys = []
         error_msgs = []

pytorch_pretrained_bert/optimization.py

@@ -53,11 +53,11 @@ class BertAdam(Optimizer):
         b1: Adams b1. Default: 0.9
         b2: Adams b2. Default: 0.999
         e: Adams epsilon. Default: 1e-6
-        weight_decay_rate: Weight decay. Default: 0.01
+        weight_decay: Weight decay. Default: 0.01
         max_grad_norm: Maximum norm for the gradients (-1 means no clipping). Default: 1.0
     """
     def __init__(self, params, lr=required, warmup=-1, t_total=-1, schedule='warmup_linear',
-                 b1=0.9, b2=0.999, e=1e-6, weight_decay_rate=0.01,
+                 b1=0.9, b2=0.999, e=1e-6, weight_decay=0.01,
                  max_grad_norm=1.0):
         if lr is not required and lr < 0.0:
             raise ValueError("Invalid learning rate: {} - should be >= 0.0".format(lr))
@@ -72,7 +72,7 @@ class BertAdam(Optimizer):
         if not e >= 0.0:
             raise ValueError("Invalid epsilon value: {} - should be >= 0.0".format(e))
         defaults = dict(lr=lr, schedule=schedule, warmup=warmup, t_total=t_total,
-                        b1=b1, b2=b2, e=e, weight_decay_rate=weight_decay_rate,
+                        b1=b1, b2=b2, e=e, weight_decay=weight_decay,
                         max_grad_norm=max_grad_norm)
         super(BertAdam, self).__init__(params, defaults)
 
@@ -140,8 +140,8 @@ class BertAdam(Optimizer):
                 # Instead we want to decay the weights in a manner that doesn't interact
                 # with the m/v parameters. This is equivalent to adding the square
                 # of the weights to the loss with plain (non-momentum) SGD.
-                if group['weight_decay_rate'] > 0.0:
-                    update += group['weight_decay_rate'] * p.data
+                if group['weight_decay'] > 0.0:
+                    update += group['weight_decay'] * p.data
 
                 if group['t_total'] != -1:
                     schedule_fct = SCHEDULES[group['schedule']]

tests/optimization_test.py

@@ -35,7 +35,7 @@ class OptimizationTest(unittest.TestCase):
         criterion = torch.nn.MSELoss(reduction='elementwise_mean')
         # No warmup, constant schedule, no gradient clipping
         optimizer = BertAdam(params=[w], lr=2e-1,
-                                          weight_decay_rate=0.0,
+                                          weight_decay=0.0,
                                           max_grad_norm=-1)
         for _ in range(100):
             loss = criterion(w, target)