[Kernel][TPU][ragged-paged-attn] vLLM code change for PR#8896 (#15659)

Signed-off-by: Yarong Mu <ymu@google.com>

requirements/tpu.txt

@@ -17,9 +17,9 @@ ray[data]
 --find-links https://storage.googleapis.com/libtpu-releases/index.html
 --find-links https://storage.googleapis.com/jax-releases/jax_nightly_releases.html
 --find-links https://storage.googleapis.com/jax-releases/jaxlib_nightly_releases.html
-torch @ https://storage.googleapis.com/pytorch-xla-releases/wheels/tpuvm/torch-2.8.0.dev20250319-cp39-cp39-linux_x86_64.whl ; python_version == "3.9"
-torch @ https://storage.googleapis.com/pytorch-xla-releases/wheels/tpuvm/torch-2.8.0.dev20250319-cp310-cp310-linux_x86_64.whl ; python_version == "3.10"
-torch @ https://storage.googleapis.com/pytorch-xla-releases/wheels/tpuvm/torch-2.8.0.dev20250319-cp311-cp311-linux_x86_64.whl ; python_version == "3.11"
-torch_xla[tpu, pallas] @ https://storage.googleapis.com/pytorch-xla-releases/wheels/tpuvm/torch_xla-2.8.0.dev20250319-cp39-cp39-linux_x86_64.whl ; python_version == "3.9"
-torch_xla[tpu, pallas] @ https://storage.googleapis.com/pytorch-xla-releases/wheels/tpuvm/torch_xla-2.8.0.dev20250319-cp310-cp310-linux_x86_64.whl ; python_version == "3.10"
-torch_xla[tpu, pallas] @ https://storage.googleapis.com/pytorch-xla-releases/wheels/tpuvm/torch_xla-2.8.0.dev20250319-cp311-cp311-linux_x86_64.whl ; python_version == "3.11"
+torch @ https://storage.googleapis.com/pytorch-xla-releases/wheels/tpuvm/torch-2.8.0.dev20250328-cp39-cp39-linux_x86_64.whl ; python_version == "3.9"
+torch @ https://storage.googleapis.com/pytorch-xla-releases/wheels/tpuvm/torch-2.8.0.dev20250328-cp310-cp310-linux_x86_64.whl ; python_version == "3.10"
+torch @ https://storage.googleapis.com/pytorch-xla-releases/wheels/tpuvm/torch-2.8.0.dev20250328-cp311-cp311-linux_x86_64.whl ; python_version == "3.11"
+torch_xla[tpu, pallas] @ https://storage.googleapis.com/pytorch-xla-releases/wheels/tpuvm/torch_xla-2.8.0.dev20250328-cp39-cp39-linux_x86_64.whl ; python_version == "3.9"
+torch_xla[tpu, pallas] @ https://storage.googleapis.com/pytorch-xla-releases/wheels/tpuvm/torch_xla-2.8.0.dev20250328-cp310-cp310-linux_x86_64.whl ; python_version == "3.10"
+torch_xla[tpu, pallas] @ https://storage.googleapis.com/pytorch-xla-releases/wheels/tpuvm/torch_xla-2.8.0.dev20250328-cp311-cp311-linux_x86_64.whl ; python_version == "3.11"

vllm/v1/attention/backends/pallas.py

@@ -41,7 +41,7 @@ class PallasAttentionBackend(AttentionBackend):
         num_kv_heads: int,
         head_size: int,
     ) -> tuple[int, ...]:
-        return (num_blocks, block_size, num_kv_heads * head_size)
+        return (num_blocks, block_size, num_kv_heads * 2, head_size)
 
     @staticmethod
     def swap_blocks(
@@ -132,7 +132,7 @@ class PallasAttentionBackendImpl(AttentionImpl):
         query: torch.Tensor,
         key: torch.Tensor,
         value: torch.Tensor,
-        kv_cache: tuple[torch.Tensor, torch.Tensor],
+        kv_cache: torch.Tensor,
         attn_metadata: PallasMetadata,
         output: Optional[torch.Tensor] = None,
     ) -> torch.Tensor:
@@ -142,14 +142,13 @@ class PallasAttentionBackendImpl(AttentionImpl):
             query: shape = [num_tokens, num_heads * head_size]
             key: shape = [num_tokens, num_kv_heads * head_size]
             value: shape = [num_tokens, num_kv_heads * head_size]
-            kv_cache = ([num_blocks, block_size, num_kv_heads * head_size], 
-                        [num_blocks, block_size, num_kv_heads * head_size])
+            kv_cache = [num_blocks, block_size, num_kv_heads * 2, head_size]
             attn_metadata: Metadata for attention.
         Returns:
             shape = [num_tokens, num_heads * head_size]
         """
         # For determine_available_memory case.
-        if kv_cache[0].numel() == 0:
+        if kv_cache.numel() == 0:
             if output is None:
                 output = torch.ones_like(query)
             return output
@@ -158,15 +157,13 @@ class PallasAttentionBackendImpl(AttentionImpl):
         num_tokens, hidden_size = query.shape
         query = query.view(num_tokens, self.num_heads, self.head_size)
 
-        key_cache, value_cache = kv_cache
-        if kv_cache[0].numel() > 0:
+        if kv_cache.numel() > 0:
             slot_mapping = attn_metadata.slot_mapping
-            write_to_kv_cache(key, value, key_cache, value_cache, slot_mapping)
+            write_to_kv_cache(key, value, kv_cache, slot_mapping)
 
         output = torch.ops.xla.ragged_paged_attention(
             query,
-            key_cache,
-            value_cache,
+            kv_cache,
             attn_metadata.context_lens,
             attn_metadata.block_tables,
             attn_metadata.query_start_loc,
@@ -183,23 +180,27 @@ class PallasAttentionBackendImpl(AttentionImpl):
 def write_to_kv_cache(
     key: torch.Tensor,
     value: torch.Tensor,
-    key_cache: torch.Tensor,
-    value_cache: torch.Tensor,
+    kv_cache: torch.Tensor,
     slot_mapping: torch.Tensor,
 ) -> None:
     """ Write the key and values to the KV cache.
 
     Args:
         key: shape = [num_tokens, num_kv_heads * head_size]
-        value: shape = [num_tokens, num_kv_heads * head_size]
-        k_cache = [num_blocks, block_size, num_kv_heads * head_size]
-        v_cache = [num_blocks, block_size, num_kv_heads * head_size]
+        value: shape = [num_tokens, num_kv_heads *  head_size]
+        kv_cache = [num_blocks, block_size, num_kv_heads * 2, head_size]
 
     """
-    torch.ops.xla.dynamo_set_buffer_donor_(key_cache, True)
-    torch.ops.xla.dynamo_set_buffer_donor_(value_cache, True)
+    _, _, num_combined_kv_heads, head_size = kv_cache.shape
+    num_kv_heads = num_combined_kv_heads // 2
 
-    key_cache = key_cache.flatten(0, 1)
-    value_cache = value_cache.flatten(0, 1)
-    key_cache.index_copy_(0, slot_mapping, key)
-    value_cache.index_copy_(0, slot_mapping, value)
+    key = key.view(-1, num_kv_heads, head_size)
+    value = value.view(-1, num_kv_heads, head_size)
+
+    kv = torch.cat([key, value], axis=-1).reshape(-1, num_combined_kv_heads,
+                                                  head_size)
+
+    torch.ops.xla.dynamo_set_buffer_donor_(kv_cache, True)
+
+    kv_cache = kv_cache.flatten(0, 1)
+    kv_cache.index_copy_(0, slot_mapping, kv)

vllm/v1/worker/tpu_model_runner.py

@@ -861,12 +861,11 @@ class TPUModelRunner:
                         kv_cache_spec.num_kv_heads, kv_cache_spec.head_size)
                     dtype = kv_cache_spec.dtype
 
-                    tpu_k_cache = torch.zeros(kv_cache_shape,
-                                              dtype=dtype,
-                                              device=self.device)
-                    tpu_v_cache = torch.zeros_like(tpu_k_cache)
+                    tpu_kv_cache = torch.zeros(kv_cache_shape,
+                                               dtype=dtype,
+                                               device=self.device)
 
-                    kv_caches[layer_name] = (tpu_k_cache, tpu_v_cache)
+                    kv_caches[layer_name] = tpu_kv_cache
                 else:
                     raise NotImplementedError
 
@@ -893,7 +892,7 @@ class ModelWrapperV1(nn.Module):
         self,
         input_ids: torch.Tensor,
         positions: torch.Tensor,
-        kv_caches: list[tuple[torch.Tensor, torch.Tensor]],
+        kv_caches: list[torch.Tensor],
         inputs_embeds: Optional[torch.Tensor] = None,
     ) -> torch.Tensor:
         """Executes the forward pass of the model.

vllm/v1/worker/tpu_worker.py

@@ -136,10 +136,10 @@ class TPUWorker:
 
                 # Use an empty tensor instead of `None`` to force Dynamo to pass
                 # it by reference, rather by specializing on the value ``None``.
-                tpu_k_cache = torch.tensor([], dtype=dtype, device=self.device)
-                tpu_v_cache = torch.tensor([], dtype=dtype, device=self.device)
-
-                kv_caches[layer_name] = (tpu_k_cache, tpu_v_cache)
+                tpu_kv_cache = torch.tensor([],
+                                            dtype=dtype,
+                                            device=self.device)
+                kv_caches[layer_name] = tpu_kv_cache
             else:
                 raise NotImplementedError