Fix unfused QKV params case; stack vs interleave option (#83)

* fix qkv weight unfused path
Signed-off-by: Kirthi Shankar Sivamani <ksivamani@nvidia.com>

* fix non FA non interleaved case
Signed-off-by: Kirthi Shankar Sivamani <ksivamani@nvidia.com>

---------
Signed-off-by: Kirthi Shankar Sivamani <ksivamani@nvidia.com>

transformer_engine/pytorch/transformer.py

@@ -24,7 +24,7 @@ from transformer_engine.pytorch.jit import (
 from transformer_engine.pytorch.utils import (
     divide,
     attention_mask_func,
-    split_tensor_along_last_dim,
+    split_tensor_along_dim,
     cast_if_needed,
     get_default_init_method,
 )
@@ -126,11 +126,11 @@ class UnfusedDotProductAttention(torch.nn.Module):
         )
 
         # [sq, b, np, hn] -> [sq, b * np, hn]
-        query_layer = query_layer.view(
+        query_layer = query_layer.reshape(
             output_size[2], output_size[0] * output_size[1], -1
         )
         # [sk, b, np, hn] -> [sk, b * np, hn]
-        key_layer = key_layer.view(output_size[3], output_size[0] * output_size[1], -1)
+        key_layer = key_layer.reshape(output_size[3], output_size[0] * output_size[1], -1)
 
         # preallocting result tensor: [b * np, sq, sk]
         matmul_result = torch.empty(
@@ -171,7 +171,7 @@ class UnfusedDotProductAttention(torch.nn.Module):
         )
 
         # change view [sk, b * np, hn]
-        value_layer = value_layer.view(
+        value_layer = value_layer.reshape(
             value_layer.size(0), output_size[0] * output_size[1], -1
         )
 
@@ -504,6 +504,7 @@ class MultiHeadAttention(torch.nn.Module):
         set_parallel_mode: bool = False,
         fuse_qkv_params: bool = False,
         zero_centered_gamma: bool = False,
+        qkv_weight_interleaved: bool = True,
     ) -> None:
         super().__init__()
         self.layer_number = (layer_number,)
@@ -515,6 +516,10 @@ class MultiHeadAttention(torch.nn.Module):
         self.params_dtype = params_dtype
         self.init_method = init_method
 
+        if not fuse_qkv_params:
+            qkv_weight_interleaved = False
+        self.qkv_weight_interleaved = qkv_weight_interleaved
+
         assert (
             attention_type in AttnTypes
         ), f"attention_type {attention_type} not supported"
@@ -703,16 +708,28 @@ class MultiHeadAttention(torch.nn.Module):
                     is_first_microbatch=is_first_microbatch,
                 )
 
+            if self.qkv_weight_interleaved:
                 # [sq, b, (np * 3 * hn)] --> [sq, b, np, 3 * hn]
                 new_tensor_shape = mixed_x_layer.size()[:-1] + (
                     self.num_attention_heads_per_partition,
                     3 * self.hidden_size_per_attention_head,
                 )
+                # split along last dimension
+                split_dim = -1
+            else:
+                # [sq, b, (np * 3 * hn)] --> [sq, b, 3 * np, hn]
+                new_tensor_shape = mixed_x_layer.size()[:-1] + (
+                    3 * self.num_attention_heads_per_partition,
+                    self.hidden_size_per_attention_head,
+                )
+                # split along second last dimension
+                split_dim = -2
+
             mixed_x_layer = mixed_x_layer.view(*new_tensor_shape)
 
-            # [sq, b, np, 3 * hn] --> 3 [sq, b, np, hn]
-            query_layer, key_layer, value_layer = split_tensor_along_last_dim(
-                mixed_x_layer, 3
+            # mixed_x_layer --> 3 [sq, b, np, hn]
+            query_layer, key_layer, value_layer = split_tensor_along_dim(
+                mixed_x_layer, split_dim, 3
             )
         else:
             # Attention heads [sk, b, h] --> [sk, b, (np * 2 * hn)]
@@ -721,15 +738,27 @@ class MultiHeadAttention(torch.nn.Module):
                 is_first_microbatch=is_first_microbatch,
             )
 
-            # [sk, b, (np * 2 * hn)] --> [sk, b, np, 2 * hn]
+            if self.qkv_weight_interleaved:
+                # [sq, b, (np * 2 * hn)] --> [sq, b, np, 2 * hn]
                 new_tensor_shape = mixed_kv_layer.size()[:-1] + (
                     self.num_attention_heads_per_partition,
                     2 * self.hidden_size_per_attention_head,
                 )
+                # split along last dimension
+                split_dim = -1
+            else:
+                # [sq, b, (np * 2 * hn)] --> [sq, b, 2 * np, hn]
+                new_tensor_shape = mixed_kv_layer.size()[:-1] + (
+                    2 * self.num_attention_heads_per_partition,
+                    self.hidden_size_per_attention_head,
+                )
+                # split along second last dimension
+                split_dim = -2
+
             mixed_kv_layer = mixed_kv_layer.view(*new_tensor_shape)
 
-            # [sk, b, np, 2 * hn] --> 2 [sk, b, np, hn]
-            (key_layer, value_layer) = split_tensor_along_last_dim(mixed_kv_layer, 2)
+            # mixed_kv_layer --> 2 [sk, b, np, hn]
+            key_layer, value_layer = split_tensor_along_dim(mixed_kv_layer, split_dim, 2)
 
             # Attention head [sq, b, h] --> [sq, b, hp]
             if self.input_layernorm:
@@ -863,7 +892,12 @@ class TransformerLayer(torch.nn.Module):
                          .. math::
                             y = \frac{x - \mathrm{E}[x]}{ \sqrt{\mathrm{Var}[x] + \varepsilon}} *
                             (1 + \gamma) + \beta
-
+    qkv_weight_interleaved : bool, default = `True`
+                            if set to `False`, the QKV weight is interpreted as a concatenation of
+                            query, key, and value weights along the `0th` dimension. The default
+                            interpretation is that the individual `q`, `k`, and `v` weights for each
+                            attention head are interleaved. This parameter is set to `False` when
+                            using :attr:`fuse_qkv_params=False`.
     Parallelism parameters
     ----------------------
     set_parallel_mode : bool, default = `False`
@@ -938,6 +972,7 @@ class TransformerLayer(torch.nn.Module):
         set_parallel_mode: bool = False,
         fuse_qkv_params: bool = False,
         zero_centered_gamma: bool = False,
+        qkv_weight_interleaved: bool = True,
     ) -> None:
         super().__init__()
 
@@ -958,6 +993,9 @@ class TransformerLayer(torch.nn.Module):
                 not fuse_wgrad_accumulation
             ), "Gradient accumulation fusion requires single QKV parameter."
 
+        if not fuse_qkv_params:
+            qkv_weight_interleaved = False
+
         self.kv_channels = (
             kv_channels if kv_channels else (hidden_size // num_attention_heads)
         )
@@ -995,6 +1033,7 @@ class TransformerLayer(torch.nn.Module):
             "set_parallel_mode": set_parallel_mode,
             "fuse_qkv_params": fuse_qkv_params,
             "zero_centered_gamma": zero_centered_gamma,
+            "qkv_weight_interleaved" : qkv_weight_interleaved,
         }
 
         self.self_attention = MultiHeadAttention(

transformer_engine/pytorch/utils.py

@@ -78,8 +78,8 @@ def divide(numerator: int, denominator: int) -> int:
     return numerator // denominator
 
 
-def split_tensor_along_last_dim(
-    tensor: torch.Tensor, num_partitions: int, contiguous_split_chunks: bool = False
+def split_tensor_along_dim(
+    tensor: torch.Tensor, dim: int, num_partitions: int, contiguous_split_chunks: bool = False
 ) -> Tuple[torch.Tensor, ...]:
     """Split a tensor along its last dimension.
     Arguments:
@@ -89,10 +89,9 @@ def split_tensor_along_last_dim(
                                  in memory.
     """
     # Get the size and dimension.
-    last_dim = tensor.dim() - 1
-    last_dim_size = divide(tensor.size()[last_dim], num_partitions)
+    split_size = divide(tensor.size()[dim], num_partitions)
     # Split.
-    tensor_list = torch.split(tensor, last_dim_size, dim=last_dim)
+    tensor_list = torch.split(tensor, split_size, dim=dim)
     # Note: torch.split does not create contiguous tensors by default.
     if contiguous_split_chunks:
         return tuple(chunk.contiguous() for chunk in tensor_list)