Or Ozeri 7ac67ea525
[KV offload][3/N] Add worker-side CPU support (#21448)
Signed-off-by: Or Ozeri <oro@il.ibm.com>
2025-09-19 09:53:45 -07:00

172 lines
6.7 KiB
Python

# SPDX-License-Identifier: Apache-2.0
# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
import numpy as np
import torch
from vllm import _custom_ops as ops
from vllm.attention import AttentionBackend
from vllm.logger import init_logger
from vllm.utils import is_pin_memory_available
from vllm.v1.kv_offload.mediums import CPULoadStoreSpec, GPULoadStoreSpec
from vllm.v1.kv_offload.worker.worker import (OffloadingHandler,
TransferResult, TransferSpec)
logger = init_logger(__name__)
def expand_block_ids(block_ids: np.ndarray,
block_size_factor: int,
output: np.ndarray,
skip_count: int = 0):
"""
Convert a list of block IDs to a list of matching block ids,
assuming each block is composed of actual block_size_factor blocks.
Outputs to output tensor.
The first skip_count blocks will be skipped.
Note that skip_count must be less than block_size_factor.
For example, if block_ids = [0, 1, 3] and block_size_factor = 4,
then it yields [0, 1, 2, 3, 4, 5, 6, 7, 12, 13, 14, 15]
since 0 maps to [0, 1, 2, 3]
1 maps to [4, 5, 6, 7]
and 3 maps to [12, 13, 14, 15]
"""
assert skip_count < block_size_factor
first_range = np.arange(skip_count, block_size_factor)
full_range = np.arange(0, block_size_factor)
output_idx = 0
for i, block_id in enumerate(block_ids):
base_block_id = block_id * block_size_factor
indices = first_range if i == 0 else full_range
output_end_idx = output_idx + len(indices)
output[output_idx:output_end_idx] = base_block_id + indices
output_idx = output_end_idx
class CpuGpuOffloadingHandler(OffloadingHandler):
def __init__(self, gpu_block_size: int, cpu_block_size: int,
num_cpu_blocks: int, gpu_caches: dict[str, torch.Tensor],
attn_backends: dict[str, type[AttentionBackend]]):
assert cpu_block_size % gpu_block_size == 0
self.block_size_factor = cpu_block_size // gpu_block_size
# cuda streams for gpu->cpu and cpu->gpu
self.d2h_stream = torch.cuda.Stream()
self.h2d_stream = torch.cuda.Stream()
# job_id -> transfer cuda event
self.transfer_events: dict[int, torch.cuda.Event] = {}
# list of cuda events available for re-use
self.events_pool: list[torch.cuda.Event] = []
pin_memory = is_pin_memory_available()
# allocate cpu tensors
logger.info("Allocating %d CPU tensors...", len(gpu_caches))
self.gpu_tensors: list[torch.Tensor] = []
self.cpu_tensors: list[torch.Tensor] = []
self.kv_dim_before_num_blocks: list[bool] = []
for layer_name, gpu_tensor in gpu_caches.items():
self.gpu_tensors.append(gpu_tensor)
gpu_shape = gpu_tensor.shape
test_shape = attn_backends[layer_name].get_kv_cache_shape(
num_blocks=1234, block_size=16, num_kv_heads=8, head_size=256)
if test_shape[0] == 1234:
# shape is (num_blocks, ...)
num_blocks_idx = 0
self.kv_dim_before_num_blocks.append(False)
else:
# shape should be (2, num_blocks, ...)
assert test_shape[0] == 2
assert test_shape[1] == 1234
assert gpu_shape[0] == 2
num_blocks_idx = 1
self.kv_dim_before_num_blocks.append(True)
cpu_shape = list(gpu_shape)
cpu_shape[num_blocks_idx] = num_cpu_blocks * self.block_size_factor
logger.debug("Allocating CPU tensor of shape %r", cpu_shape)
self.cpu_tensors.append(
torch.zeros(cpu_shape,
dtype=gpu_tensor.dtype,
device="cpu",
pin_memory=pin_memory))
def transfer_async(self, job_id: int, spec: TransferSpec) -> bool:
src_spec, dst_spec = spec
if isinstance(src_spec, CPULoadStoreSpec):
assert isinstance(dst_spec, GPULoadStoreSpec)
stream = self.h2d_stream
src_tensors = self.cpu_tensors
dst_tensors = self.gpu_tensors
src_block_size_factor = self.block_size_factor
dst_block_size_factor = 1
else:
assert isinstance(src_spec, GPULoadStoreSpec)
assert isinstance(dst_spec, CPULoadStoreSpec)
stream = self.d2h_stream
src_tensors = self.gpu_tensors
dst_tensors = self.cpu_tensors
src_block_size_factor = 1
dst_block_size_factor = self.block_size_factor
src_blocks = src_spec.block_ids
dst_blocks = dst_spec.block_ids
assert src_blocks.ndim == 1
assert dst_blocks.ndim == 1
dst_sub_blocks_to_skip = (-src_blocks.size % dst_block_size_factor)
src_sub_block_count = src_blocks.size * src_block_size_factor
assert (
src_sub_block_count == dst_blocks.size * dst_block_size_factor -
dst_sub_blocks_to_skip)
src_to_dst = np.empty((src_sub_block_count, 2), dtype=np.int64)
expand_block_ids(src_blocks, src_block_size_factor, src_to_dst[:, 0])
expand_block_ids(dst_blocks,
dst_block_size_factor,
src_to_dst[:, 1],
skip_count=dst_sub_blocks_to_skip)
src_to_dst_tensor = torch.from_numpy(src_to_dst)
event = self.events_pool.pop() if self.events_pool \
else torch.cuda.Event()
with torch.cuda.stream(stream):
for src_tensor, dst_tensor, kv_dim in zip(
src_tensors, dst_tensors, self.kv_dim_before_num_blocks):
if kv_dim:
src_key_cache = src_tensor[0]
dst_key_cache = dst_tensor[0]
ops.swap_blocks(src_key_cache, dst_key_cache,
src_to_dst_tensor)
src_value_cache = src_tensor[1]
dst_value_cache = dst_tensor[1]
ops.swap_blocks(src_value_cache, dst_value_cache,
src_to_dst_tensor)
else:
ops.swap_blocks(src_tensor, dst_tensor, src_to_dst_tensor)
event.record(stream)
self.transfer_events[job_id] = event
# success
return True
def get_finished(self) -> list[TransferResult]:
results: list[TransferResult] = []
for job_id, event in self.transfer_events.items():
if event.query():
results.append((job_id, True))
self.events_pool.append(event)
for job_id, _ in results:
del self.transfer_events[job_id]
return results