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https://git.datalinker.icu/vllm-project/vllm.git
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339 lines
14 KiB
Python
339 lines
14 KiB
Python
# SPDX-License-Identifier: Apache-2.0
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from collections import defaultdict
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from collections.abc import Iterable
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from typing import Optional
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from vllm.logger import init_logger
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from vllm.utils import cdiv
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from vllm.v1.core.block_pool import BlockPool
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from vllm.v1.core.kv_cache_utils import (BlockHashType, KVCacheBlock,
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hash_request_tokens)
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from vllm.v1.metrics.stats import PrefixCacheStats
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from vllm.v1.request import Request, RequestStatus
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logger = init_logger(__name__)
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class KVCacheManager:
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def __init__(
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self,
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block_size: int,
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num_gpu_blocks: int,
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max_model_len: int,
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sliding_window: Optional[int] = None,
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enable_caching: bool = True,
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num_preallocate_tokens: int = 64,
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log_stats: bool = False,
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) -> None:
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self.block_size = block_size
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self.num_gpu_blocks = num_gpu_blocks
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self.max_model_len = max_model_len
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self.max_num_blocks_per_req = cdiv(max_model_len, block_size)
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self.sliding_window = sliding_window
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self.enable_caching = enable_caching
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# FIXME: make prefix cache stats conditional on log_stats
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self.log_stats = log_stats
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# NOTE(woosuk): To avoid frequent block allocation, we preallocate some
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# blocks for each request. For example, when a request reaches the end
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# of its block table, we preallocate N blocks in advance. This way, we
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# reduce the overhead of updating free_block_ids and ref_cnts for each
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# request every step (at the cost of some memory waste).
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# NOTE(woosuk): This is different from the "lookahead" slots since this
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# does not guarantee that the request always has N empty blocks. After
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# the request gets N empty blocks, it starts to use the blocks without
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# further allocation. When it uses up all the N empty blocks, it gets
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# N new empty blocks.
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self.num_preallocate_tokens = num_preallocate_tokens
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self.num_preallocate_blocks = cdiv(num_preallocate_tokens, block_size)
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self.block_pool = BlockPool(num_gpu_blocks, enable_caching)
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# Mapping from request ID to blocks to track the blocks allocated
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# for each request, so that we can free the blocks when the request
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# is finished.
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self.req_to_blocks: defaultdict[str,
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list[KVCacheBlock]] = defaultdict(list)
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# Mapping from request ID to kv block hashes.
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# This is to avoid recomputing the block hashes for each call of
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# `get_computed_blocks` or `allocate_slots`.
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self.req_to_block_hashes: defaultdict[
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str, list[BlockHashType]] = defaultdict(list)
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# {req_id: The number of cached blocks for this given request}
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# This is used to track the number of cached blocks for each request.
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# This is only used to track the RUNNING requests, we do not track the
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# data for reempted ones.
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self.num_cached_block: dict[str, int] = {}
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self.prefix_cache_stats = PrefixCacheStats()
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@property
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def usage(self) -> float:
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"""Get the KV cache usage.
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Returns:
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The KV cache usage (between 0.0 and 1.0).
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"""
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return self.block_pool.get_usage()
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def make_prefix_cache_stats(self) -> PrefixCacheStats:
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"""Get (and reset) the prefix cache stats.
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Returns:
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The current prefix caching stats.
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"""
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stats = self.prefix_cache_stats
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self.prefix_cache_stats = PrefixCacheStats()
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return stats
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def get_computed_blocks(
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self, request: Request) -> tuple[list[KVCacheBlock], int]:
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"""Get the computed (cached) blocks for the request.
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Note that the computed blocks must be full.
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Args:
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request: The request to get the computed blocks.
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Returns:
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A tuple containing:
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- A list of blocks that are computed for the request.
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- The number of computed tokens.
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"""
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if not self.enable_caching:
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# Prefix caching is disabled.
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return [], 0
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computed_blocks = []
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# The block hashes for the request may already be computed
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# if the scheduler has tried to schedule the request before.
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block_hashes = self.req_to_block_hashes[request.request_id]
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if not block_hashes:
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block_hashes = hash_request_tokens(self.block_size, request)
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self.req_to_block_hashes[request.request_id] = block_hashes
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for block_hash in block_hashes:
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# block_hashes is a chain of block hashes. If a block hash is not
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# in the cached_block_hash_to_id, the following block hashes are
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# not computed yet for sure.
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if cached_block := self.block_pool.get_cached_block(block_hash):
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computed_blocks.append(cached_block)
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else:
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break
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self.prefix_cache_stats.requests += 1
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self.prefix_cache_stats.queries += len(block_hashes)
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self.prefix_cache_stats.hits += len(computed_blocks)
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# NOTE(woosuk): Since incomplete blocks are not eligible for
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# sharing, `num_computed_tokens` is always a multiple of
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# `block_size`.
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num_computed_tokens = len(computed_blocks) * self.block_size
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return computed_blocks, num_computed_tokens
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def allocate_slots(
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self,
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request: Request,
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num_tokens: int,
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new_computed_blocks: Optional[list[KVCacheBlock]] = None
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) -> Optional[list[KVCacheBlock]]:
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"""Add slots for a request with new tokens to append.
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Args:
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request: The request to allocate slots.
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num_tokens: The number of tokens to allocate. Note that this does
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not include the tokens that have already been computed.
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new_computed_blocks: A list of new computed blocks just hitting the
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prefix caching.
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Blocks layout:
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-----------------------------------------------------------------------
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| < computed > | < new computed > | < new > | < pre-allocated > |
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-----------------------------------------------------------------------
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| < required > |
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--------------------------------------------------
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| < full > |
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------------------------------------------------
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| <new full> |
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--------------
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The following *_blocks are illustrated in this layout.
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Returns:
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A list of new allocated blocks.
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"""
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if num_tokens == 0:
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raise ValueError("num_tokens must be greater than 0")
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new_computed_blocks = new_computed_blocks or []
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# The number of computed tokens is the number of computed tokens plus
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# the new prefix caching hits
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num_computed_tokens = (request.num_computed_tokens +
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len(new_computed_blocks) * self.block_size)
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num_required_blocks = cdiv(num_computed_tokens + num_tokens,
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self.block_size)
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req_blocks = self.req_to_blocks[request.request_id]
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num_new_blocks = (num_required_blocks - len(req_blocks) -
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len(new_computed_blocks))
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# If a computed block of a request is an eviction candidate (in the
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# free queue and ref_cnt == 0), it cannot be counted as a free block
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# when allocating this request.
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num_evictable_computed_blocks = sum(1 for blk in new_computed_blocks
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if blk.ref_cnt == 0)
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if (num_new_blocks > self.block_pool.get_num_free_blocks() -
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num_evictable_computed_blocks):
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# Cannot allocate new blocks
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return None
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# Touch the computed blocks to make sure they won't be evicted.
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if self.enable_caching:
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self.block_pool.touch(new_computed_blocks)
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else:
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assert not new_computed_blocks, (
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"Computed blocks should be empty when "
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"prefix caching is disabled")
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# Append the new computed blocks to the request blocks until now to
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# avoid the case where the new blocks cannot be allocated.
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req_blocks.extend(new_computed_blocks)
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# Start to handle new blocks
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if num_new_blocks <= 0:
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# No new block is needed.
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new_blocks = []
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else:
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# Get new blocks from the free block pool considering
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# preallocated blocks.
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num_new_blocks = min(
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num_new_blocks + self.num_preallocate_blocks,
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self.block_pool.get_num_free_blocks(),
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# Should not exceed the maximum number of blocks per request.
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# This is especially because the block table has the shape
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# [..., max_num_blocks_per_req].
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self.max_num_blocks_per_req - len(req_blocks),
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)
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assert num_new_blocks > 0
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# Concatenate the computed block IDs and the new block IDs.
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new_blocks = self.block_pool.get_new_blocks(num_new_blocks)
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req_blocks.extend(new_blocks)
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if not self.enable_caching:
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return new_blocks
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# Use `new_computed_blocks` for a new request, and `num_cached_block`
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# for a running request.
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num_cached_blocks = self.num_cached_block.get(request.request_id,
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len(new_computed_blocks))
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# Speculated tokens might be rejected in the future, so we does
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# not cache any speculated tokens. We only cache blocks with
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# generated (accepted) tokens.
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num_full_blocks_after_append = (num_computed_tokens + num_tokens - len(
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request.spec_token_ids)) // self.block_size
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self.block_pool.cache_full_blocks(
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request=request,
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blocks=req_blocks,
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block_hashes=self.req_to_block_hashes[request.request_id],
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num_cached_blocks=num_cached_blocks,
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num_full_blocks=num_full_blocks_after_append,
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block_size=self.block_size,
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)
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self.num_cached_block[
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request.request_id] = num_full_blocks_after_append
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return new_blocks
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def free(self, request: Request) -> None:
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"""Free the blocks allocated for the request.
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When caching is enabled, we free the blocks in reverse order so that
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the tail blocks are evicted first.
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Args:
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request: The request to free the blocks.
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"""
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# Default to [] in case a request is freed (aborted) before alloc.
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blocks = self.req_to_blocks.pop(request.request_id, [])
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ordered_blocks: Iterable[KVCacheBlock] = blocks
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if self.enable_caching:
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# Free blocks in reverse order so that the tail blocks are
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# freed first.
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ordered_blocks = reversed(blocks)
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self.block_pool.free_blocks(ordered_blocks)
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self.num_cached_block.pop(request.request_id, None)
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def reset_prefix_cache(self) -> bool:
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"""Reset prefix cache. This function may be used in RLHF
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flows to invalid prefix caching after the weights are updated,
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or used for resetting prefix caching status for benchmarking.
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Returns:
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bool: True if the prefix cache is successfully reset,
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False otherwise.
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"""
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if self.block_pool.reset_prefix_cache():
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self.prefix_cache_stats.reset = True
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return True
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return False
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def get_num_common_prefix_blocks(
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self,
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request: Request,
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num_running_requests: int,
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) -> int:
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"""Calculate the number of common prefix blocks shared by all requests
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in the RUNNING state.
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The function determines this by selecting any request and iterating
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through its blocks. A block is considered a common prefix block if its
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`ref_cnt` equals the total number of requests in the RUNNING state.
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NOTE(woosuk): The number of requests in the RUNNING state is **greater
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than or equal to** the number of requests scheduled in the current step.
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This is because the RUNNING state only indicates that:
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1. The request has not yet finished, and
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2. The request holds its blocks unfreed.
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While all scheduled requests must be in the RUNNING state, the inverse
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is not necessarily true. There may be RUNNING requests that are not
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scheduled in the current step.
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This can result in an edge case where the number of common prefix blocks
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is 0, even though all scheduled requests share a common prefix. This
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occurs because there may be unscheduled RUNNING requests that do not
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share the common prefix. Currently, this case cannot be easily detected,
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so the function returns 0 in such cases.
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Args:
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request: Any request in the RUNNING state, used to identify the
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common prefix blocks.
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num_running_requests: The total number of requests in the RUNNING
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state. This can be different from the number of scheduled
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requests in the current step.
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Returns:
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int: The number of common prefix blocks.
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"""
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assert request.status == RequestStatus.RUNNING
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blocks = self.req_to_blocks[request.request_id]
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num_common_blocks = 0
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for block in blocks:
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if block.ref_cnt == num_running_requests:
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num_common_blocks += 1
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else:
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break
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return num_common_blocks
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def free_block_hashes(self, request: Request) -> None:
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"""Discard the block hashes for the request.
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NOTE: Unlike `free`, this method should be called only when the request
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is finished, not when it is preempted.
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"""
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self.req_to_block_hashes.pop(request.request_id, None)
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