Merge pull request #8 from laekov/simple_mlp

Simple mlp

examples/transformer-xl/mem_transformer.py

@@ -384,11 +384,29 @@ class CustomizedMoEPositionwiseFF(FMoETransformerMLP):
             nn.Dropout(dropout)
         )
         super().__init__(num_expert=moe_num_expert, d_model=d_model, d_hidden=d_inner, top_k=moe_top_k,
-                do_lnorm=True, pre_lnorm=pre_lnorm, activation=activation, dropout=dropout)
+                activation=activation)
 
-    def forward(self, x):
-        x = super().forward(x)
-        return x
+        self.pre_lnorm = pre_lnorm
+        self.layer_norm = nn.LayerNorm(d_model)
+        self.dropout = nn.Dropout(dropout)
+
+    def forward(self, inp):
+        if self.pre_lnorm:
+            ##### layer normalization + positionwise feed-forward
+            core_out = super().forward(self.layer_norm(inp))
+            core_out = self.dropout(core_out)
+
+            ##### residual connection
+            output = core_out + inp
+        else:
+            ##### positionwise feed-forward
+            core_out = super().forward(inp)
+            core_out = self.dropout(core_out)
+
+            ##### residual connection + layer normalization
+            output = self.layer_norm(inp + core_out)
+
+        return output
 
 class DecoderLayer(nn.Module):
     def __init__(self, n_head, d_model, d_head, d_inner, dropout, **kwargs):

fmoe/layers.py

@@ -61,22 +61,33 @@ class FMoELinear(nn.Module):
         '''
         x = MOELinear.apply(inp, self.weight, fwd_expert_count)
         if self.bias is not None:
-            # TODO: torch.repeat_interleave seems have wrong
-            # behaviors in backward, leading to incorrect
-            # gradient computation for bias.
-            # Thus we use a for-loop to manually expand the bias.
-            # This part should finally goes to MOELinear.apply.
-            # bias = torch.repeat_interleave(self.bias,
-            #        fwd_expert_count.to(self.bias.device), dim=0)
-            bias = []
-            for i in range(self.num_expert):
-                if fwd_expert_count[i] > 0:
-                    bias.append(
-                        self.bias[i].unsqueeze(0).expand(
-                            fwd_expert_count[i], -1
-                        )
-                    )
-            bias = torch.cat(bias, dim=0)
+            # TODO: torch.repeat_interleave seems have numerical
+            # instability in backward, leading to incorrect
+            # gradient computation for solution 1 and 2.
+            # Solution 3 uses a for-loop to expand the bias,
+            # but is 50% slower.
+            # This part should finally goes to MOELinear.apply,
+            # like MOELinear.apply(x, weight, bias, count)
+
+            # Solution 1
+            bias = torch.repeat_interleave(self.bias,
+                fwd_expert_count.to(self.bias.device), dim=0)
+
+            # Solution 2
+            # bias_idx = torch.arange(self.num_expert)\
+            #     .repeat_interleave(fwd_expert_count)
+            # bias = self.bias[bias_idx]
+
+            # Solution 3
+            # bias = []
+            # for i in range(self.num_expert):
+            #    if fwd_expert_count[i] > 0:
+            #        bias.append(
+            #            self.bias[i].unsqueeze(0).expand(
+            #                fwd_expert_count[i], -1
+            #            )
+            #        )
+            # bias = torch.cat(bias, dim=0)
             x = x + bias
         return x
 

fmoe/megatron.py

@@ -3,8 +3,6 @@ The adaptor to seamlessly enable FastMoE in Megatron-LM v2.0 with at most two
 lines of modification.
 See `examples/megatron` for usage instructions.
 '''
-import torch
-
 from .transformer import FMoETransformerMLP
 from .distributed import DistributedGroupedDataParallel
 from .utils import get_torch_default_comm
@@ -28,12 +26,10 @@ class MegatronMLP(FMoETransformerMLP):
                 d_model=args.hidden_size, d_hidden=args.hidden_hidden_size,
                 world_size=world_size, mp_group=group,
                 expert_dp_comm='none' if args.distributed_experts else 'dp')
-        self.bias = torch.nn.parameter.Parameter(
-            torch.zeros(args.hidden_size, dtype=torch.float32)
-        )
-
     def forward(self, inp):
-        return super().forward(inp), self.bias
+        output = super().forward(inp)
+        bias = output.new_zeros(output.size(-1), requires_grad=False)
+        return output, bias
 
 
 def fmoefy(model, num_experts=None, distributed_experts=True,

fmoe/transformer.py

@@ -44,25 +44,15 @@ class FMoETransformerMLP(FMoE):
         d_hidden=4096,
         world_size=1,
         mp_group=None,
-        activation=torch.nn.functional.gelu,
+        activation=torch.nn.GELU(),
         gate=NaiveGate,
         top_k=2,
-        do_lnorm=False,
-        pre_lnorm=False,
         expert_dp_comm='none',
-        dropout=0.1
     ):
         super().__init__(num_expert=num_expert, d_model=d_model, gate=gate,
                 top_k=top_k, world_size=world_size, mp_group=mp_group)
-        self.dropout = nn.Dropout(dropout)
         self.experts = _Expert(num_expert, d_model, d_hidden, activation,
                 rank=self.mp_rank)
-        self.pre_lnorm = pre_lnorm
-        if do_lnorm:
-            self.layer_norm = nn.LayerNorm(d_model)
-            self.pre_lnorm = pre_lnorm
-        else:
-            self.pre_lnorm = None
         self.mark_parallel_comm(expert_dp_comm)
 
     def forward(self, inp: torch.Tensor):
@@ -72,11 +62,5 @@ class FMoETransformerMLP(FMoE):
         '''
         original_shape = inp.shape
         inp = inp.reshape(-1, self.d_model)
-        if self.pre_lnorm is not None and self.pre_lnorm:
-            inp = self.layer_norm(inp)
         output = super().forward(inp)
-        output = self.dropout(output)
-        output += inp
-        if self.pre_lnorm is not None and not self.pre_lnorm:
-            output = self.layer_norm(output)
         return output.reshape(original_shape)