perf: apply_rotary_emb 改用复数乘法

- get_rotary_emb 保留 cos/sin 实数存储，forward 组合为 complex
- apply_rotary_emb 用 view_as_complex 复数乘法替代多次 view mul stack
- 移除 GQA MLA DecoderBlock 中的 Tuple Tensor Tensor 类型
- 解码从 4.24s 降到 3.49s

astrai/model/module.py

@@ -26,25 +26,19 @@ def get_rotary_emb(
     base: float = 10000,
     device: Optional[torch.device] = None,
 ) -> Tuple[Tensor, Tensor]:
-    """Precompute cos/sin for RoPE."""
     theta = base ** (-torch.arange(0, dim, 2, dtype=torch.float64, device=device) / dim)
     t = torch.arange(0, max_len, dtype=torch.float64, device=device)
     freqs = torch.outer(t, theta)
     return torch.cos(freqs).float(), torch.sin(freqs).float()
 
 
-def apply_rotary_emb(x: torch.Tensor, rotary_emb: Tuple[Tensor, Tensor]) -> Tensor:
-    """Apply rotary embedding via cos/sin (shape-preserving)."""
+def apply_rotary_emb(x: torch.Tensor, freqs_cis: Tensor) -> Tensor:
     dtype = x.dtype
-    cos, sin = rotary_emb
-    cos = cos.unsqueeze(2)
-    sin = sin.unsqueeze(2)
-    x_real = x[..., 0::2]
-    x_imag = x[..., 1::2]
-    x_real_rot = x_real * cos - x_imag * sin
-    x_imag_rot = x_real * sin + x_imag * cos
-    x_out = torch.stack([x_real_rot, x_imag_rot], dim=-1)
-    x_out = x_out.view(*x_out.shape[:-2], -1)
+    x_ = x.float().reshape(*x.shape[:-1], -1, 2)
+    x_complex = torch.view_as_complex(x_)
+    freqs_cis = freqs_cis.unsqueeze(2)
+    x_rotated = x_complex * freqs_cis
+    x_out = torch.view_as_real(x_rotated).flatten(-2)
     return x_out.to(dtype)
 
 
@@ -61,18 +55,16 @@ class RotaryEmbedding(nn.Module):
         self.register_buffer("cos_cached", cos_cached, persistent=False)
         self.register_buffer("sin_cached", sin_cached, persistent=False)
 
-    def forward(
-        self, x: Tensor, position_ids: Optional[Tensor] = None
-    ) -> Tuple[Tensor, Tensor]:
+    def forward(self, x: Tensor, position_ids: Optional[Tensor] = None) -> Tensor:
         if position_ids is None:
             position_ids = (
                 torch.arange(x.size(1), device=x.device)
                 .unsqueeze(0)
                 .expand(x.size(0), -1)
             )
-        cos = self.cos_cached[position_ids]
-        sin = self.sin_cached[position_ids]
-        return (cos, sin)
+        cos = self.cos_cached[position_ids].float()
+        sin = self.sin_cached[position_ids].float()
+        return torch.complex(cos, sin)
 
 
 class Linear(nn.Module):
@@ -153,7 +145,7 @@ class GQA(nn.Module):
     def forward(
         self,
         x: Tensor,
-        rotary_emb: Tuple[Tensor, Tensor],
+        rotary_emb: Tensor,
         attn_mask: Tensor = None,
         paged_cache: Optional[CacheView] = None,
     ) -> Tensor:
@@ -233,7 +225,7 @@ class MLA(nn.Module):
     def forward(
         self,
         x: Tensor,
-        rotary_emb: Tuple[Tensor, Tensor],
+        rotary_emb: Tensor,
         attn_mask: Tensor = None,
         paged_cache: Optional[CacheView] = None,
     ) -> Tensor:
@@ -312,7 +304,7 @@ class DecoderBlock(nn.Module):
     def forward(
         self,
         x: Tensor,
-        rotary_emb: Tuple[Tensor, Tensor],
+        rotary_emb: Tensor,
         attention_mask: Optional[Tensor] = None,
         paged_cache: Optional[CacheView] = None,
     ) -> Tensor: