[Hardware][TPU]Enable ragged paged attention kernel and resolve recompilation issue (#14310)

Signed-off-by: Chengji Yao <chengjiyao@google.com>

requirements-tpu.txt

@@ -17,9 +17,9 @@ ray[default]
 --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-2.7.0.dev20250227%2Bcxx11-cp39-cp39-linux_x86_64.whl ; python_version == "3.9"
-torch @ https://storage.googleapis.com/pytorch-xla-releases/wheels/tpuvm/torch-2.7.0.dev20250227%2Bcxx11-cp310-cp310-linux_x86_64.whl ; python_version == "3.10"
-torch @ https://storage.googleapis.com/pytorch-xla-releases/wheels/tpuvm/torch-2.7.0.dev20250227%2Bcxx11-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-2.7.0.dev20250227%2Bcxx11-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-2.7.0.dev20250227%2Bcxx11-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-2.7.0.dev20250227%2Bcxx11-cp311-cp311-linux_x86_64.whl ; python_version == "3.11"
+torch @ https://storage.googleapis.com/pytorch-xla-releases/wheels/tpuvm/torch-2.7.0.dev20250306%2Bcxx11-cp39-cp39-linux_x86_64.whl ; python_version == "3.9"
+torch @ https://storage.googleapis.com/pytorch-xla-releases/wheels/tpuvm/torch-2.7.0.dev20250306%2Bcxx11-cp310-cp310-linux_x86_64.whl ; python_version == "3.10"
+torch @ https://storage.googleapis.com/pytorch-xla-releases/wheels/tpuvm/torch-2.7.0.dev20250306%2Bcxx11-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-2.7.0.dev20250306%2Bcxx11-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-2.7.0.dev20250306%2Bcxx11-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-2.7.0.dev20250306%2Bcxx11-cp311-cp311-linux_x86_64.whl ; python_version == "3.11"

vllm/v1/attention/backends/pallas.py

@@ -12,7 +12,7 @@ from vllm.attention.backends.abstract import (AttentionBackend, AttentionImpl,
 from vllm.attention.backends.utils import CommonAttentionState
 
 # These are the 2 tunable parameters of the paged attention Pallas kernel.
-NUM_QUERIES_PER_BLOCK = 16
+NUM_QUERIES_PER_BLOCK = 32
 NUM_KV_PAGES_PER_BLOCK = 128
 
 
@@ -41,7 +41,7 @@ class PallasAttentionBackend(AttentionBackend):
         num_kv_heads: int,
         head_size: int,
     ) -> tuple[int, ...]:
-        return (num_kv_heads, num_blocks, block_size, head_size)
+        return (num_blocks, block_size, num_kv_heads, head_size)
 
     @staticmethod
     def swap_blocks(
@@ -115,6 +115,17 @@ class PallasAttentionBackendImpl(AttentionImpl):
                                       "are not implemented for "
                                       "PallasAttentionBackendImpl")
 
+        tpu_version = torch_xla.tpu.version()
+        if tpu_version < 4:
+            raise NotImplementedError("TPU version must be 4 or higher.")
+        # NOTE(chengjiyao): the TPU v4's vmem capacity is 16MB
+        # TODO(chengjiyao): autotune NUM_QUERIES_PER_BLOCK,
+        # NUM_KV_PAGES_PER_BLOCK and vmem_limit_bytes
+        if tpu_version == 4:
+            self.vmem_limit_bytes = 16 * 1024 * 1024
+        else:
+            self.vmem_limit_bytes = 64 * 1024 * 1024
+
     def forward(
         self,
         layer: AttentionLayer,
@@ -131,8 +142,8 @@ 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_kv_heads, num_blocks, block_size, head_size], 
-                        [num_kv_heads, num_blocks, block_size, head_size])
+            kv_cache = ([num_blocks, block_size, num_kv_heads, head_size], 
+                        [num_blocks, block_size, num_kv_heads, head_size])
             attn_metadata: Metadata for attention.
         Returns:
             shape = [num_tokens, num_heads * head_size]
@@ -154,10 +165,6 @@ class PallasAttentionBackendImpl(AttentionImpl):
             slot_mapping = attn_metadata.slot_mapping
             write_to_kv_cache(key, value, key_cache, value_cache, slot_mapping)
 
-        query = query * self.scale
-        # use_kernel switches between using kernel or reference implementation
-        # (non kernel: https://github.com/pytorch/xla/blob/cee0820e78fc9675e2d0511db891fd44342e890d/torch_xla/experimental/custom_kernel.py#L890).
-        use_kernel = False
         output = torch.ops.xla.ragged_paged_attention(
             query,
             key_cache,
@@ -168,8 +175,9 @@ class PallasAttentionBackendImpl(AttentionImpl):
             attn_metadata.num_seqs,
             num_kv_pages_per_block=NUM_KV_PAGES_PER_BLOCK,
             num_queries_per_block=NUM_QUERIES_PER_BLOCK,
-            use_kernel=use_kernel,
-        )
+            vmem_limit_bytes=self.vmem_limit_bytes,
+            use_kernel=True,
+            sm_scale=self.scale)
 
         return output.reshape(num_tokens, hidden_size)
 
@@ -186,16 +194,15 @@ def write_to_kv_cache(
     Args:
         key: shape = [num_tokens, num_kv_heads, head_size]
         value: shape = [num_tokens, num_kv_heads, head_size]
-        k_cache = [num_kv_heads, num_blocks, block_size, head_size]
-        v_cache = [num_kv_heads, num_blocks, block_size, head_size]
+        k_cache = [num_blocks, block_size, num_kv_heads, head_size]
+        v_cache = [num_blocks, block_size, num_kv_heads, head_size]
 
     """
     torch.ops.xla.dynamo_set_buffer_donor_(key_cache, True)
     torch.ops.xla.dynamo_set_buffer_donor_(value_cache, True)
 
-    key = key.flatten(0, 1)
-    value = value.flatten(0, 1)
-    key_cache = key_cache.flatten(0, 2)
-    value_cache = value_cache.flatten(0, 2)
+    key_cache = key_cache.flatten(0, 1)
+    value_cache = value_cache.flatten(0, 1)
+    slot_mapping = slot_mapping.flatten()
     key_cache.index_copy_(0, slot_mapping, key)
     value_cache.index_copy_(0, slot_mapping, value)

vllm/v1/worker/tpu_model_runner.py

@@ -14,7 +14,7 @@ import torch_xla.runtime as xr
 from vllm.attention.backends.abstract import AttentionType
 from vllm.attention.layer import Attention
 from vllm.config import VllmConfig
-from vllm.forward_context import get_forward_context, set_forward_context
+from vllm.forward_context import set_forward_context
 from vllm.inputs import INPUT_REGISTRY
 from vllm.logger import init_logger
 from vllm.model_executor.model_loader import get_model
@@ -416,8 +416,8 @@ class TPUModelRunner:
             num_scheduled_tokens_per_req)
 
         # Do the padding and copy the tensors to the TPU.
-        padded_total_num_scheduled_tokens = _get_padded_number(
-            total_num_scheduled_tokens, NUM_QUERIES_PER_BLOCK)
+        padded_total_num_scheduled_tokens = _get_padded_token_len(
+            total_num_scheduled_tokens)
         self.input_ids = self.input_ids_cpu[:
                                             padded_total_num_scheduled_tokens].to(
                                                 self.device)
@@ -428,23 +428,22 @@ class TPUModelRunner:
         slot_mapping = self.slot_mapping_cpu[:
                                              padded_total_num_scheduled_tokens].to(
                                                  self.device)
-        padded_block_table = self.block_table_cpu[:
-                                                  padded_total_num_scheduled_tokens]
-        padded_block_table[:num_reqs, :self.max_num_blocks_per_req] = (
+        block_tables = self.block_table_cpu[:self.max_num_reqs]
+        block_tables[:num_reqs, :self.max_num_blocks_per_req] = (
             self.input_batch.block_table.get_cpu_tensor()[:num_reqs])
-        padded_block_table = padded_block_table.to(self.device)
-        query_start_loc = self.query_start_loc_cpu[:
-                                                   padded_total_num_scheduled_tokens
-                                                   + 1].to(self.device)
-        seq_lens = self.seq_lens_cpu[:padded_total_num_scheduled_tokens].to(
+        block_tables = block_tables.to(self.device)
+        query_start_loc = self.query_start_loc_cpu[:self.max_num_reqs + 1].to(
             self.device)
+        seq_lens = self.seq_lens_cpu[:self.max_num_reqs].to(self.device)
 
         attn_metadata = PallasMetadata(
             slot_mapping=slot_mapping,
-            block_tables=padded_block_table,
+            block_tables=block_tables,
             context_lens=seq_lens,
             query_start_loc=query_start_loc,
-            num_seqs=num_reqs,
+            num_seqs=torch.tensor([num_reqs],
+                                  dtype=torch.int32,
+                                  device=self.device),
         )
         # NOTE(woosuk): Due to chunked prefills, there can be at most 1 partial
         # request in the batch. While we should not sample any token from this
@@ -693,29 +692,34 @@ class TPUModelRunner:
                                     dtype=torch.int32,
                                     device=self.device)
             inputs_embeds = None
+        actual_num_reqs = min(num_tokens, self.max_num_reqs)
         position_ids = torch.zeros(num_tokens,
                                    dtype=torch.int32,
                                    device=self.device)
         slot_mapping = torch.zeros(num_tokens,
                                    dtype=torch.int64,
                                    device=self.device)
-        block_tables = torch.zeros((num_tokens, self.block_table_cpu.shape[1]),
-                                   dtype=torch.int32,
-                                   device=self.device)
-        query_lens = [1] * num_tokens
+        block_tables = torch.zeros(
+            (self.max_num_reqs, self.block_table_cpu.shape[1]),
+            dtype=torch.int32,
+            device=self.device)
+        query_lens = [1] * self.max_num_reqs
         query_start_loc = torch.cumsum(torch.tensor([0] + query_lens,
                                                     dtype=torch.int32),
                                        dim=0,
                                        dtype=torch.int32).to(self.device)
-        context_lens = torch.ones((num_tokens, ),
+        context_lens = torch.ones((self.max_num_reqs, ),
                                   dtype=torch.int32,
                                   device=self.device)
+        num_seqs = torch.tensor([actual_num_reqs],
+                                dtype=torch.int32,
+                                device=self.device)
         attn_metadata = PallasMetadata(
             slot_mapping=slot_mapping,
             block_tables=block_tables,
             context_lens=context_lens,
             query_start_loc=query_start_loc,
-            num_seqs=num_tokens,
+            num_seqs=num_seqs,
         )
 
         if self.is_multimodal_model:
@@ -724,9 +728,6 @@ class TPUModelRunner:
             torch._dynamo.mark_dynamic(input_ids, 0)
         torch._dynamo.mark_dynamic(position_ids, 0)
         torch._dynamo.mark_dynamic(attn_metadata.slot_mapping, 0)
-        torch._dynamo.mark_dynamic(attn_metadata.block_tables, 0)
-        torch._dynamo.mark_dynamic(attn_metadata.query_start_loc, 0)
-        torch._dynamo.mark_dynamic(attn_metadata.context_lens, 0)
 
         with set_forward_context(attn_metadata, self.vllm_config, 0):
             assert self.model is not None
@@ -817,28 +818,6 @@ class ModelWrapperV1(nn.Module):
             inputs_embeds: The input embeddings of shape [num_tokens,
                 hidden_size]. It is used for multimodal models.
         """
-        # Skip this in memory profiling at initialization.
-        if kv_caches[0][0].numel() > 0:
-            attn_metadata = get_forward_context().attn_metadata
-            # index_copy_(slot_mapping) only works when the inserted dimension
-            # is 0. However, the KV cache in the Pallas backend has the shape
-            # [num_kv_heads, num_blocks, block_size, head_size]. To make it
-            # work, we need to flatten the first three dimensions and modify
-            # the slot_mapping accordingly.
-            # kv_caches: list[tuple[torch.Tensor, torch.Tensor]]
-            num_kv_heads, num_blocks, block_size, _ = kv_caches[0][0].shape
-            slot_mapping = attn_metadata.slot_mapping
-            slot_mapping = slot_mapping.flatten()
-            head_indicies = torch.arange(0,
-                                         num_kv_heads,
-                                         device=slot_mapping.device,
-                                         dtype=slot_mapping.dtype)
-            head_indicies *= block_size * num_blocks
-            slot_mapping = slot_mapping.repeat_interleave(num_kv_heads).view(
-                -1, num_kv_heads)
-            slot_mapping = slot_mapping + head_indicies.view(1, -1)
-            slot_mapping = slot_mapping.flatten()
-            attn_metadata.slot_mapping = slot_mapping
 
         assert self.model is not None
         hidden_states = self.model(
@@ -866,3 +845,9 @@ class ModelWrapperV1(nn.Module):
 
 def _get_padded_number(n: int, multiple: int) -> int:
     return ((n + multiple - 1) // multiple) * multiple
+
+
+def _get_padded_token_len(x: int) -> int:
+    if x <= 16:
+        return 16
+    return 1 << (x - 1).bit_length()