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352 lines
14 KiB
Python
352 lines
14 KiB
Python
# SPDX-License-Identifier: Apache-2.0
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from collections import defaultdict
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from dataclasses import dataclass
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from typing import Optional
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from vllm.distributed.kv_events import KVCacheEvent
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from vllm.logger import init_logger
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from vllm.utils import sha256
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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.core.specialized_manager import get_manager_for_kv_cache_spec
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from vllm.v1.kv_cache_interface import KVCacheConfig
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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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@dataclass
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class KVCacheBlocks:
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blocks: list[KVCacheBlock]
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def __add__(self, other: "KVCacheBlocks") -> "KVCacheBlocks":
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"""Adds two KVCacheBlocks instances."""
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return KVCacheBlocks(self.blocks + other.blocks)
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@classmethod
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def create_empty(cls) -> "KVCacheBlocks":
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"""Creates a new KVCacheBlocks instance with no blocks."""
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return cls([])
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def get_block_ids(self) -> list[int]:
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"""Converts the KVCacheBlocks instance to a list of block IDs."""
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return [block.block_id for block in self.blocks]
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class KVCacheManager:
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def __init__(
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self,
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kv_cache_config: KVCacheConfig,
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max_model_len: int,
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enable_caching: bool = True,
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caching_hash_algo: str = "builtin",
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use_eagle: bool = False,
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log_stats: bool = False,
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enable_kv_cache_events: bool = False,
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) -> None:
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assert len(kv_cache_config.kv_cache_groups) == 1, (
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"KVCacheManager does not support hybrid models with more than 1 "
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"kv cache group")
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kv_cache_spec = kv_cache_config.kv_cache_groups[0].kv_cache_spec
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self.block_size = kv_cache_spec.block_size
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self.num_gpu_blocks = kv_cache_config.num_blocks
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self.max_model_len = max_model_len
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self.enable_caching = enable_caching
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self.caching_hash_fn = sha256 if caching_hash_algo == "sha256" else hash
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self.use_eagle = use_eagle
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self.log_stats = log_stats
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# FIXME: make prefix cache stats conditional on log_stats
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self.prefix_cache_stats = PrefixCacheStats() if log_stats else None
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self.block_pool = BlockPool(self.num_gpu_blocks, enable_caching,
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enable_kv_cache_events)
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self.single_type_manager = get_manager_for_kv_cache_spec(
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kv_cache_spec=kv_cache_spec,
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block_pool=self.block_pool,
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use_eagle=self.use_eagle,
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num_kv_cache_groups=1,
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caching_hash_fn=self.caching_hash_fn,
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)
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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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@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) -> Optional[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, or None if logging is disabled.
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"""
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if not self.log_stats:
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return None
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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(self,
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request: Request) -> tuple[KVCacheBlocks, 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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# Prefix caching is disabled or
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# When the request requires prompt logprobs, we skip prefix caching.
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if (not self.enable_caching
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or request.sampling_params.prompt_logprobs is not None):
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return KVCacheBlocks.create_empty(), 0
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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.caching_hash_fn,
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self.block_size, request)
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self.req_to_block_hashes[request.request_id] = block_hashes
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if self.log_stats:
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assert self.prefix_cache_stats is not None
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self.prefix_cache_stats.requests += 1
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if len(block_hashes) * self.block_size == request.num_tokens:
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# When prompt length is divisible by the block size and all
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# blocks are cached, we need to recompute the last token. This
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# have to be achieved by re-computing an entire block because
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# allocate_slots() assumes num_computed_tokens is always a
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# multiple of the block size. To achieve this, remove the last
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# block hash from the block_hashes for find_longest_cache_hit
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# This limitation can potentially be removed in the future to
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# slightly improve the performance.
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last_block_hash = block_hashes.pop()
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else:
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last_block_hash = None
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computed_blocks = (
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self.single_type_manager.find_longest_cache_hit(block_hashes))
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if self.log_stats:
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assert self.prefix_cache_stats is not None
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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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if last_block_hash is not None:
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# Add back the last block hash if it was removed.
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# NOTE: Because block_hashes is cached in req_to_block_hashes,
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# we shouldn't modify it directly.
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block_hashes.append(last_block_hash)
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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 KVCacheBlocks(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_new_tokens: int,
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new_computed_blocks: Optional[KVCacheBlocks] = None,
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num_lookahead_tokens: int = 0,
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) -> Optional[KVCacheBlocks]:
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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_new_tokens: The number of tokens to allocate, including external
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tokens. Note that this does not include tokens that have
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already been computed locally (i.e. new_computed_blocks).
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new_computed_blocks: The new computed blocks just hitting the
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prefix caching.
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num_lookahead_tokens: The number of speculative tokens to allocate.
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This is used by spec decode proposers with kv-cache such
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as eagle.
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Blocks layout:
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```
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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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```
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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_new_tokens == 0:
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raise ValueError("num_new_tokens must be greater than 0")
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if new_computed_blocks is not None:
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new_computed_block_list = new_computed_blocks.blocks
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else:
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new_computed_block_list = []
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# Free the blocks that are skipped during the attention computation
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# (e.g., tokens outside the sliding window).
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# We can do this even if we cannot schedule this request due to
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# insufficient free blocks.
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# Should call this function before allocating new blocks to reduce
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# the number of evicted blocks.
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self.single_type_manager.remove_skipped_blocks(
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request.request_id, request.num_computed_tokens)
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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_block_list) * self.block_size)
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num_tokens_need_slot = min(
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num_computed_tokens + num_new_tokens + num_lookahead_tokens,
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self.max_model_len)
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num_blocks_to_allocate = (
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self.single_type_manager.get_num_blocks_to_allocate(
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request_id=request.request_id,
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num_tokens=num_tokens_need_slot,
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new_computed_blocks=new_computed_block_list,
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))
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if num_blocks_to_allocate > self.block_pool.get_num_free_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_block_list)
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else:
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assert not new_computed_block_list, (
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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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self.single_type_manager.save_new_computed_blocks(
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request.request_id, new_computed_block_list)
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new_blocks = self.single_type_manager.allocate_new_blocks(
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request.request_id, num_tokens_need_slot)
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if not self.enable_caching:
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return KVCacheBlocks(new_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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self.single_type_manager.cache_blocks(
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request, self.req_to_block_hashes[request.request_id],
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num_computed_tokens + num_new_tokens - len(request.spec_token_ids))
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return KVCacheBlocks(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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We free the blocks in reverse order so that he tail blocks are evicted
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first when caching is enabled.
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Args:
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request: The request to free the blocks.
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"""
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self.single_type_manager.free(request.request_id)
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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 invalidate 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 not self.block_pool.reset_prefix_cache():
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return False
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if self.log_stats:
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assert self.prefix_cache_stats is not None
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self.prefix_cache_stats.reset = True
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return True
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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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return self.single_type_manager.get_num_common_prefix_blocks(
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request.request_id, num_running_requests)
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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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def take_events(self) -> list[KVCacheEvent]:
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"""Take the KV cache events from the block pool.
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Returns:
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A list of KV cache events.
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"""
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return self.block_pool.take_events()
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