added faster L2 grad clipping and new torch gelu

megatron/arguments.py

@@ -122,6 +122,10 @@ def _add_network_size_args(parser):
                        action='store_true',
                        help='If set, use original BERT residula connection '
                        'ordering.')
+    group.add_argument('--openai-gelu', action='store_true',
+                       help='Use OpenAIs GeLU implementation. This option'
+                       'should not be used unless for backward compatibility'
+                       'reasons.')
 
     return parser
 

megatron/model/bert_model.py

@@ -18,16 +18,15 @@
 import torch
 
 from megatron import get_args
+from megatron.model.language_model import parallel_lm_logits
+from megatron.model.language_model import get_language_model
+from megatron.model.transformer import LayerNorm
+from megatron.model.utils import openai_gelu
+from megatron.model.utils import get_linear_layer
+from megatron.model.utils import init_method_normal
+from megatron.model.utils import scaled_init_method_normal
 from megatron.module import MegatronModule
 
-from .language_model import parallel_lm_logits
-from .language_model import get_language_model
-from .transformer import LayerNorm
-from .utils import gelu
-from .utils import get_linear_layer
-from .utils import init_method_normal
-from .utils import scaled_init_method_normal
-
 
 def bert_attention_mask_func(attention_scores, attention_mask):
     attention_scores = attention_scores + attention_mask
@@ -82,6 +81,8 @@ class BertLMHead(MegatronModule):
 
         super(BertLMHead, self).__init__()
 
+        args = get_args()
+        
         self.bias = torch.nn.Parameter(torch.zeros(mpu_vocab_size))
         self.bias.model_parallel = True
         self.bias.partition_dim = 0
@@ -90,10 +91,13 @@ class BertLMHead(MegatronModule):
 
         self.dense = get_linear_layer(hidden_size, hidden_size, init_method)
         self.layernorm = LayerNorm(hidden_size, eps=layernorm_epsilon)
+        self.gelu = torch.nn.functional.gelu
+        if args.openai_gelu:
+            self.gelu = openai_gelu
 
     def forward(self, hidden_states, word_embeddings_weight):
         hidden_states = self.dense(hidden_states)
-        hidden_states = gelu(hidden_states)
+        hidden_states = self.gelu(hidden_states)
         hidden_states = self.layernorm(hidden_states)
         output = parallel_lm_logits(hidden_states,
                                     word_embeddings_weight,

megatron/model/language_model.py

@@ -21,9 +21,8 @@ import torch.nn.functional as F
 from megatron import get_args
 from megatron import mpu
 from megatron.module import MegatronModule
-
 from megatron.model.transformer import ParallelTransformer
-from megatron.model.utils import gelu
+from megatron.model.utils import openai_gelu
 from megatron.model.utils import get_linear_layer
 
 
@@ -47,6 +46,12 @@ def parallel_lm_logits(input_, word_embeddings_weight, parallel_output,
 def get_language_model(attention_mask_func, num_tokentypes, add_pooler,
                        init_method, scaled_init_method):
     """Build language model and return along with the key to save."""
+    args = get_args()
+
+    # Use torch gelu unless otherwise forced.
+    gelu = F.gelu
+    if args.openai_gelu:
+        gelu = openai_gelu
     
     # Language model.
     language_model = TransformerLanguageModel(

megatron/model/utils.py

@@ -54,9 +54,7 @@ def gelu_impl(x):
     """OpenAI's gelu implementation."""
     return 0.5 * x * (1.0 + torch.tanh(0.7978845608028654 * x *
                                        (1.0 + 0.044715 * x * x)))
-
-
-def gelu(x):
+def openai_gelu(x):
     return gelu_impl(x)
 
 

megatron/mpu/grads.py

@@ -21,10 +21,47 @@
 import torch
 from torch._six import inf
 
+from apex.multi_tensor_apply import multi_tensor_applier
+import amp_C
+
 from .initialize import get_model_parallel_group
 from .initialize import get_model_parallel_rank
 
 
+def l2_grad_clipper(parameters, max_norm):
+    """Efficient L2 norm gradient clipping."""
+
+    overflow_buf = torch.zeros(1, dtype=torch.int, device='cuda')
+    if isinstance(parameters, torch.Tensor):
+        parameters = [parameters]
+    mp_rank_is_zero = (get_model_parallel_rank() == 0)
+    parameters = list(filter(lambda p: (p.grad is not None) and
+                             (p.model_parallel or mp_rank_is_zero),
+                             parameters))
+    norm, _ = multi_tensor_applier(
+        amp_C.multi_tensor_l2norm,
+        overflow_buf,
+        [parameters],
+        False # no per-parameter norm
+    )
+    # Sum across all model parallel GPUs.
+    norm_2 = norm * norm
+    torch.distributed.all_reduce(norm_2,
+                                 op=torch.distributed.ReduceOp.SUM,
+                                 group=get_model_parallel_group())
+    total_norm = norm_2.item() ** 0.5
+
+    clip_coef = max_norm / (total_norm + 1e-6)
+    grads = [p.grad for p in parameters]
+    if clip_coef < 1:
+        multi_tensor_applier(
+            amp_C.multi_tensor_scale,
+            overflow_buf,
+            [grads, grads],
+            clip_coef)
+    return total_norm
+
+
 def clip_grad_norm(parameters, max_norm, norm_type=2):
     """Clips gradient norm of an iterable of parameters.
 
@@ -55,6 +92,13 @@ def clip_grad_norm(parameters, max_norm, norm_type=2):
                                      op=torch.distributed.ReduceOp.MAX,
                                      group=get_model_parallel_group())
         total_norm = total_norm_cuda[0].item()
+        clip_coef = max_norm / (total_norm + 1e-6)
+        if clip_coef < 1:
+            for p in parameters:
+                p.grad.data.mul_(clip_coef)
+    elif norm_type == 2:
+        total_norm = l2_grad_clipper(parameters, max_norm)
+
     else:
         total_norm = 0
         for p in parameters: