HiCache Storage TP Refinement (#8307)

Co-authored-by: pansicheng <sicheng.pan.chn@gmail.com>

python/sglang/srt/managers/cache_controller.py

@@ -219,6 +219,7 @@ class HiCacheController:
         token_to_kv_pool_allocator: BaseTokenToKVPoolAllocator,
         mem_pool_host: HostKVCache,
         page_size: int,
+        tp_group: torch.distributed.ProcessGroup,
         load_cache_event: threading.Event = None,
         write_policy: str = "write_through_selective",
         io_backend: str = "",
@@ -244,11 +245,17 @@ class HiCacheController:
         self.enable_storage = False
         # todo: move backend initialization to storage backend module
         if storage_backend is not None:
+            # create a new communication group for synchronizing storage operations across TP workers
+            self.tp_world_size = torch.distributed.get_world_size(group=tp_group)
+            if self.tp_world_size > 1:
+                group_ranks = torch.distributed.get_process_group_ranks(tp_group)
+                self.tp_group = torch.distributed.new_group(group_ranks, backend="gloo")
+
             if storage_backend == "file":
                 self.storage_backend = HiCacheFile()
                 self.enable_storage = True
                 # todo: threshold policy for prefetching
-                self.prefetch_threshold = prefetch_threshold
+                self.prefetch_threshold = max(prefetch_threshold, self.page_size)
             else:
                 raise NotImplementedError(
                     f"Unsupported storage backend: {storage_backend}"
@@ -568,13 +575,32 @@ class HiCacheController:
                     else:
                         break
 
+                if self.tp_world_size > 1:
+                    storage_hit_count_tensor = torch.tensor(
+                        storage_hit_count, dtype=torch.int
+                    )
+                    torch.distributed.all_reduce(
+                        storage_hit_count_tensor,
+                        op=torch.distributed.ReduceOp.MIN,
+                        group=self.tp_group,
+                    )
+                    storage_hit_count = storage_hit_count_tensor.item()
+
                 if storage_hit_count < self.prefetch_threshold:
                     # not to prefetch if not enough benefits
                     self.prefetch_revoke_queue.put(operation.request_id)
+                    logger.debug(
+                        f"Revoking prefetch for request {operation.request_id} due to insufficient hits ({storage_hit_count})."
+                    )
                 else:
-                    operation.hash_value = hash_value
+                    operation.hash_value = hash_value[
+                        : (storage_hit_count // self.page_size)
+                    ]
+                    # free the pre-allocated memory for pages that are not hit
+                    self.mem_pool_host.free(operation.host_indices[storage_hit_count:])
+                    operation.host_indices = operation.host_indices[:storage_hit_count]
                     logger.debug(
-                        f"Prefetching {len(hash_value)} pages for request {operation.request_id}."
+                        f"Prefetching {len(operation.hash_value)} pages for request {operation.request_id}."
                     )
                     self.prefetch_buffer.put(operation)
 
@@ -611,17 +637,37 @@ class HiCacheController:
                     last_hash = get_hash_str(
                         tokens_to_backup[i : i + self.page_size], last_hash
                     )
-                    # todo, handle failures in storage backend
-                    self.storage_backend.set(
+                    success = self.storage_backend.set(
                         last_hash,
                         self.mem_pool_host.get_flat_data_page(
                             operation.host_indices[i]
                         ),
                     )
+                    if not success:
+                        logger.warning(f"Failed to write page {last_hash} to storage.")
+                        break
                     operation.completed_tokens += self.page_size
                     operation.hash_value.append(last_hash)
 
-                self.ack_backup_queue.put((operation.id, operation.hash_value))
+                min_completed_tokens = operation.completed_tokens
+                if self.tp_world_size > 1:
+                    completed_tokens_tensor = torch.tensor(
+                        min_completed_tokens, dtype=torch.int
+                    )
+                    torch.distributed.all_reduce(
+                        completed_tokens_tensor,
+                        op=torch.distributed.ReduceOp.MIN,
+                        group=self.tp_group,
+                    )
+                    min_completed_tokens = completed_tokens_tensor.item()
+
+                self.ack_backup_queue.put(
+                    (
+                        operation.id,
+                        operation.hash_value[: min_completed_tokens // self.page_size],
+                        min_completed_tokens,
+                    )
+                )
 
             except Empty:
                 continue

python/sglang/srt/mem_cache/hicache_storage.py

@@ -9,6 +9,12 @@ import torch
 logger = logging.getLogger(__name__)
 
 
+from sglang.srt.distributed import (
+    get_tensor_model_parallel_rank,
+    get_tensor_model_parallel_world_size,
+)
+
+
 def get_hash_str(token_ids: List[int], prior_hash: Optional[str] = None) -> str:
     hasher = hashlib.sha256()
 
@@ -80,13 +86,20 @@ class HiCacheFile(HiCacheStorage):
 
     def __init__(self, file_path: str = "/tmp/hicache"):
         self.file_path = file_path
-        if not os.path.exists(self.file_path):
+        tp_rank = get_tensor_model_parallel_rank()
+        tp_size = get_tensor_model_parallel_world_size()
+        self.tp_suffix = f"_{tp_rank}_{tp_size}" if tp_size > 1 else ""
+        if not os.path.exists(self.file_path) and tp_rank == 0:
             os.makedirs(self.file_path)
             logger.info(f"Created HiCacheFile storage directory at {self.file_path}")
 
+    def _get_suffixed_key(self, key: str) -> str:
+        return key + self.tp_suffix
+
     def get(
         self, key: str, target_location: Optional[torch.Tensor] = None
     ) -> torch.Tensor | None:
+        key = self._get_suffixed_key(key)
         tensor_path = os.path.join(self.file_path, f"{key}.bin")
         try:
             # todo: fixing the target_location logic to enable in-place loading
@@ -112,6 +125,7 @@ class HiCacheFile(HiCacheStorage):
         ]
 
     def set(self, key: str, value: torch.Tensor) -> bool:
+        key = self._get_suffixed_key(key)
         tensor_path = os.path.join(self.file_path, f"{key}.bin")
         if self.exists(key):
             logger.debug(f"Key {key} already exists. Skipped.")
@@ -130,10 +144,12 @@ class HiCacheFile(HiCacheStorage):
         return True
 
     def exists(self, key: str) -> bool:
+        key = self._get_suffixed_key(key)
         tensor_path = os.path.join(self.file_path, f"{key}.bin")
         return os.path.exists(tensor_path)
 
     def delete(self, key: str) -> None:
+        key = self._get_suffixed_key(key)
         tensor_path = os.path.join(self.file_path, f"{key}.bin")
         try:
             os.remove(tensor_path)

python/sglang/srt/mem_cache/hiradix_cache.py

@@ -50,6 +50,7 @@ class HiRadixCache(RadixCache):
             raise ValueError(f"HiRadixCache only supports MHA and MLA yet")
 
         self.tp_group = tp_cache_group
+        self.tp_world_size = torch.distributed.get_world_size(group=self.tp_group)
         self.enable_storage = hicache_storage_backend is not None
         # todo: customizable storage prefetch threshold
         self.prefetch_threshold = 256
@@ -59,6 +60,7 @@ class HiRadixCache(RadixCache):
             token_to_kv_pool_allocator,
             self.token_to_kv_pool_host,
             page_size,
+            self.tp_group,
             load_cache_event=self.load_cache_event,
             write_policy=hicache_write_policy,
             io_backend=hicache_io_backend,
@@ -153,7 +155,7 @@ class HiRadixCache(RadixCache):
         queue_size = torch.tensor(
             self.cache_controller.ack_write_queue.qsize(), dtype=torch.int
         )
-        if torch.distributed.get_world_size(group=self.tp_group) > 1:
+        if self.tp_world_size > 1:
             # synchrnoize TP workers to make the same update to radix cache
             torch.distributed.all_reduce(
                 queue_size,
@@ -353,7 +355,7 @@ class HiRadixCache(RadixCache):
         queue_size = torch.tensor(
             self.cache_controller.prefetch_revoke_queue.qsize(), dtype=torch.int
         )
-        if torch.distributed.get_world_size(group=self.tp_group) > 1:
+        if self.tp_world_size > 1:
             # synchrnoize TP workers to make the same update to hiradix cache
             torch.distributed.all_reduce(
                 queue_size,
@@ -372,7 +374,7 @@ class HiRadixCache(RadixCache):
         queue_size = torch.tensor(
             self.cache_controller.ack_backup_queue.qsize(), dtype=torch.int
         )
-        if torch.distributed.get_world_size(group=self.tp_group) > 1:
+        if self.tp_world_size > 1:
             # synchrnoize TP workers to make the same update to hiradix cache
             torch.distributed.all_reduce(
                 queue_size,
@@ -380,9 +382,15 @@ class HiRadixCache(RadixCache):
                 group=self.tp_group,
             )
         for _ in range(queue_size.item()):
-            ack_id, hash_value = self.cache_controller.ack_backup_queue.get()
-            self.ongoing_backup[ack_id].hash_value = hash_value
-            self.ongoing_backup[ack_id].release_host()
+            ack_id, hash_value, completed_tokens = (
+                self.cache_controller.ack_backup_queue.get()
+            )
+            host_node = self.ongoing_backup[ack_id]
+            if completed_tokens < len(host_node.key):
+                # backup is only partially successful, split the node
+                new_node = self._split_node(host_node.key, host_node, completed_tokens)
+                new_node.hash_value = hash_value
+            host_node.release_host()
             del self.ongoing_backup[ack_id]
 
     def check_prefetch_progress(self, req_id: str):
@@ -400,15 +408,18 @@ class HiRadixCache(RadixCache):
         )
         logger.debug(f"Prefetch {req_id} completed with {completed_tokens} tokens")
 
-        min_completed_tokens = torch.tensor(completed_tokens, dtype=torch.int)
-        if torch.distributed.get_world_size(group=self.tp_group) > 1:
+        min_completed_tokens = completed_tokens
+        if self.tp_world_size > 1:
             # synchrnoize TP workers to make the same update to hiradix cache
+            completed_tokens_tensor = torch.tensor(
+                min_completed_tokens, dtype=torch.int
+            )
             torch.distributed.all_reduce(
-                min_completed_tokens,
+                completed_tokens_tensor,
                 op=torch.distributed.ReduceOp.MIN,
                 group=self.tp_group,
             )
-        min_completed_tokens = min_completed_tokens.item()
+            min_completed_tokens = completed_tokens_tensor.item()
         fetched_token_ids = token_ids[:min_completed_tokens]
         written_indices = host_indices[:min_completed_tokens]
         matched_length = self._insert_helper_host(
@@ -465,16 +476,19 @@ class HiRadixCache(RadixCache):
         new_input_tokens: List[int],
         last_hash: Optional[str] = None,
     ):
-        if not self.enable_storage or len(new_input_tokens) < self.prefetch_threshold:
+        # align the number of fetching tokens to the page size
+        prefetch_length = len(new_input_tokens) - (
+            len(new_input_tokens) % self.page_size
+        )
+        new_input_tokens = new_input_tokens[:prefetch_length]
+        if not self.enable_storage or prefetch_length < self.prefetch_threshold:
             return
 
         last_host_node.protect_host()
-        host_indices = self.cache_controller.mem_pool_host.alloc(len(new_input_tokens))
+        host_indices = self.cache_controller.mem_pool_host.alloc(prefetch_length)
         if host_indices is None:
-            self.evict_host(len(new_input_tokens))
-            host_indices = self.cache_controller.mem_pool_host.alloc(
-                len(new_input_tokens)
-            )
+            self.evict_host(prefetch_length)
+            host_indices = self.cache_controller.mem_pool_host.alloc(prefetch_length)
         if host_indices is None:
             last_host_node.release_host()
             # no sufficient host memory to prefetch

python/sglang/srt/mem_cache/memory_pool_host.py

@@ -126,6 +126,9 @@ class HostKVCache(abc.ABC):
 
     @synchronized()
     def alloc(self, need_size: int) -> torch.Tensor:
+        assert (
+            need_size % self.page_size == 0
+        ), "The requested size should be a multiple of the page size."
         if need_size > self.available_size():
             return None