[Misc] Clean up RoPE forward_native (vllm-project#8076)

vllm/model_executor/layers/rotary_embedding.py

@@ -28,7 +28,6 @@
 import torch.nn as nn
 
 from vllm.model_executor.custom_op import CustomOp
-from vllm.platforms import current_platform
 
 
 def _rotate_neox(x: torch.Tensor) -> torch.Tensor:
@@ -48,21 +47,29 @@ def _apply_rotary_emb(
     x: torch.Tensor,
     cos: torch.Tensor,
     sin: torch.Tensor,
+    is_neox_style: bool,
 ) -> torch.Tensor:
     """
     Args:
         x: [num_tokens, num_heads, head_size]
         cos: [num_tokens, head_size // 2]
         sin: [num_tokens, head_size // 2]
+        is_neox_style: Whether to use the Neox-style or GPT-J-style rotary
+            positional embeddings.
     """
-    orig_dtype = x.dtype
-    x = x.float()
-    x1, x2 = torch.chunk(x, 2, dim=-1)
-    cos = cos.unsqueeze(-2)
-    sin = sin.unsqueeze(-2)
+    cos = cos.unsqueeze(-2).to(x.dtype)
+    sin = sin.unsqueeze(-2).to(x.dtype)
+    if is_neox_style:
+        x1, x2 = torch.chunk(x, 2, dim=-1)
+    else:
+        x1 = x[..., ::2]
+        x2 = x[..., 1::2]
     o1 = x1 * cos - x2 * sin
     o2 = x2 * cos + x1 * sin
-    return torch.cat((o1, o2), dim=-1).to(orig_dtype)
+    if is_neox_style:
+        return torch.cat((o1, o2), dim=-1)
+    else:
+        return torch.stack((o1, o2), dim=-1).flatten(-2)
 
 
 class RotaryEmbedding(CustomOp):
@@ -87,10 +94,9 @@ def __init__(
 
         cache = self._compute_cos_sin_cache()
         cache = cache.to(dtype)
+        self.cos_sin_cache: torch.Tensor
         self.register_buffer("cos_sin_cache", cache, persistent=False)
 
-        self.use_native2 = current_platform.is_tpu() and is_neox_style
-
     def _compute_inv_freq(self, base: Union[int, float]) -> torch.Tensor:
         """Compute the inverse frequency."""
         # NOTE(woosuk): To exactly match the HF implementation, we need to
@@ -119,59 +125,7 @@ def forward_native(
         key: torch.Tensor,
         offsets: Optional[torch.Tensor] = None,
     ) -> Tuple[torch.Tensor, torch.Tensor]:
-        """A PyTorch-native implementation equivalent to forward().
-
-        This method mimics the implementation of the custom CUDA kernel
-        used in `forward_cuda()`.
-        """
-        query = query.view(*query.shape[:-1], -1, self.head_size)
-        key = key.view(*key.shape[:-1], -1, self.head_size)
-
-        query_rot = query[..., :self.rotary_dim]
-        key_rot = key[..., :self.rotary_dim]
-        if self.rotary_dim < self.head_size:
-            query_pass = query[..., self.rotary_dim:]
-            key_pass = key[..., self.rotary_dim:]
-
-        self.cos_sin_cache: torch.Tensor = self.cos_sin_cache.to(
-            positions.device, dtype=query.dtype)
-        cos_sin = self.cos_sin_cache[torch.add(positions, offsets)
-                                     if offsets is not None else positions]
-        cos, sin = cos_sin.chunk(2, dim=-1)
-        if self.is_neox_style:
-            # NOTE(woosuk): Here we assume that the positions tensor has the
-            # shape [batch_size, seq_len].
-            cos = cos.repeat(1, 1, 2).unsqueeze(-2)
-            sin = sin.repeat(1, 1, 2).unsqueeze(-2)
-        else:
-            cos = cos.repeat_interleave(2, dim=-1).unsqueeze(-2)
-            sin = sin.repeat_interleave(2, dim=-1).unsqueeze(-2)
-
-        rotate_fn = _rotate_neox if self.is_neox_style else _rotate_gptj
-        query_rot = query_rot * cos + rotate_fn(query_rot) * sin
-        key_rot = key_rot * cos + rotate_fn(key_rot) * sin
-
-        if self.rotary_dim < self.head_size:
-            query = torch.cat((query_rot, query_pass), dim=-1)
-            key = torch.cat((key_rot, key_pass), dim=-1)
-        else:
-            query = query_rot
-            key = key_rot
-        query = query.flatten(-2)
-        key = key.flatten(-2)
-        return query, key
-
-    def forward_native2(
-        self,
-        positions: torch.Tensor,
-        query: torch.Tensor,
-        key: torch.Tensor,
-        offsets: Optional[torch.Tensor] = None,
-    ) -> Tuple[torch.Tensor, torch.Tensor]:
-        """Another PyTorch-native implementation of forward().
-
-        This method might perform better than `forward_native()` when compiled.
-        """
+        """A PyTorch-native implementation of forward()."""
         if offsets is not None:
             positions = positions + offsets
         positions = positions.flatten()
@@ -183,14 +137,14 @@ def forward_native2(
         query = query.view(num_tokens, -1, self.head_size)
         query_rot = query[..., :self.rotary_dim]
         query_pass = query[..., self.rotary_dim:]
-        query_rot = _apply_rotary_emb(query_rot, cos, sin)
+        query_rot = _apply_rotary_emb(query_rot, cos, sin, self.is_neox_style)
         query = torch.cat((query_rot, query_pass), dim=-1).reshape(query_shape)
 
         key_shape = key.shape
         key = key.view(num_tokens, -1, self.head_size)
         key_rot = key[..., :self.rotary_dim]
         key_pass = key[..., self.rotary_dim:]
-        key_rot = _apply_rotary_emb(key_rot, cos, sin)
+        key_rot = _apply_rotary_emb(key_rot, cos, sin, self.is_neox_style)
         key = torch.cat((key_rot, key_pass), dim=-1).reshape(key_shape)
         return query, key
 
@@ -203,7 +157,7 @@ def forward_cuda(
     ) -> Tuple[torch.Tensor, torch.Tensor]:
         from vllm import _custom_ops as ops
 
-        self.cos_sin_cache = self.cos_sin_cache.to(positions.device,
+        self.cos_sin_cache = self.cos_sin_cache.to(query.device,
                                                    dtype=query.dtype)
         # ops.rotary_embedding()/batched_rotary_embedding()
         # are in-place operations that update the query and key tensors.
@@ -240,17 +194,6 @@ def forward_xpu(
                                  self.cos_sin_cache, self.is_neox_style)
         return query, key
 
-    def forward_tpu(
-        self,
-        positions: torch.Tensor,
-        query: torch.Tensor,
-        key: torch.Tensor,
-        offsets: Optional[torch.Tensor] = None,
-    ) -> Tuple[torch.Tensor, torch.Tensor]:
-        forward_fn = (self.forward_native2
-                      if self.use_native2 else self.forward_native)
-        return forward_fn(positions, query, key, offsets)
-
     def extra_repr(self) -> str:
         s = f"head_size={self.head_size}, rotary_dim={self.rotary_dim}"
         s += f", max_position_embeddings={self.max_position_embeddings}"