Merge branch 'sequence_parallel' into 'main'

fix for sequence parallelism in bert pooling

See merge request ADLR/megatron-lm!418

megatron/model/language_model.py

@@ -116,7 +116,9 @@ class Pooler(MegatronModule):
         # gather data along sequence dimensions
         # same pooler is run on all tensor parallel nodes
         if self.sequence_parallel:
-            hidden_states = mpu.gather_from_sequence_parallel_region(hidden_states)
+            hidden_states = mpu.gather_from_sequence_parallel_region(
+                hidden_states,
+                to_model_parallel=False)
 
         pooled = hidden_states[sequence_index, :, :]
         pooled = self.dense(pooled)

megatron/mpu/mappings.py

@@ -214,19 +214,25 @@ class _ScatterToSequenceParallelRegion(torch.autograd.Function):
 
 
 class _GatherFromSequenceParallelRegion(torch.autograd.Function):
-    """Gather the input from model parallel region and concatinate.""" #TODO
+    """Gather the input from sequence parallel region and concatinate.""" 
 
     @staticmethod
-    def symbolic(graph, input_):
+    def symbolic(graph, input_, to_model_parallel=True):
         return _gather_along_first_dim(input_)
     
     @staticmethod
-    def forward(ctx, input_):
+    def forward(ctx, input_, to_model_parallel=True):
+        ctx.to_model_parallel = to_model_parallel
         return _gather_along_first_dim(input_)
 
     @staticmethod
     def backward(ctx, grad_output):
-        return _reduce_scatter_along_first_dim(grad_output)
+        to_model_parallel = ctx.to_model_parallel
+
+        if to_model_parallel:
+            return _reduce_scatter_along_first_dim(grad_output), None
+        else:
+            return _split_along_first_dim(grad_output), None
 
 
 class _ReduceScatterToSequenceParallelRegion(torch.autograd.Function):
@@ -269,8 +275,8 @@ def scatter_to_sequence_parallel_region(input_):
     return _ScatterToSequenceParallelRegion.apply(input_)
 
 
-def gather_from_sequence_parallel_region(input_):
-    return _GatherFromSequenceParallelRegion.apply(input_)
+def gather_from_sequence_parallel_region(input_, to_model_parallel=True):
+    return _GatherFromSequenceParallelRegion.apply(input_, to_model_parallel)
 
 
 def reduce_scatter_to_sequence_parallel_region(input_):