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enginex-ascend-910-vllm/vllm_ascend/kv_offload/cpu_npu.py

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from collections import deque
from dataclasses import dataclass
import numpy as np
import torch
from vllm.logger import logger
from vllm.utils.platform_utils import is_pin_memory_available
from vllm.v1.attention.backend import AttentionBackend # type: ignore
from vllm.v1.kv_offload.mediums import CPULoadStoreSpec, GPULoadStoreSpec
from vllm.v1.kv_offload.worker.worker import OffloadingHandler, TransferResult, TransferSpec
@dataclass
class Transfer:
job_id: int
stream: torch.npu.Stream
start_event: torch.npu.Event
end_event: torch.npu.Event
num_bytes: int
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
# Vectorized: compute all sub-block IDs at once
bases = block_ids * block_size_factor
offsets = np.arange(block_size_factor)
# shape: (num_blocks, block_size_factor) -> ravel to 1D
all_ids = (bases[:, None] + offsets[None, :]).ravel()
# Skip the first skip_count elements (only affects first block)
if skip_count > 0:
all_ids = all_ids[skip_count:]
output[: len(all_ids)] = all_ids
class CpuNpuOffloadingHandler(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
# npu streams for npu->cpu and cpu->npu
self.d2h_stream = torch.npu.Stream()
self.h2d_stream = torch.npu.Stream()
# Ordered queue of in-flight transfers per direction
self._d2h_transfers: deque[Transfer] = deque()
self._h2d_transfers: deque[Transfer] = deque()
# Reusable event pool to avoid allocation overhead
self._event_pool: list[torch.npu.Event] = []
pin_memory = is_pin_memory_available()
# allocate cpu tensors
logger.info("Allocating %d CPU tensors...", len(gpu_caches))
self.npu_tensors: list[torch.Tensor] = []
self.cpu_tensors: list[torch.Tensor] = []
for layer_name, gpu_tensor in gpu_caches.items():
self.npu_tensors.append(gpu_tensor)
gpu_shape = gpu_tensor[0].shape
num_blocks_idx = 0
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[0].dtype,
device="cpu",
pin_memory=pin_memory,
),
torch.zeros(
cpu_shape,
dtype=gpu_tensor[0].dtype,
device="cpu",
pin_memory=pin_memory,
),
)
)
# Pre-compute base pointers and block sizes for batch copies.
# In vllm-ascend, each layer's KV cache is stored as a tuple
# (key_cache, value_cache), so we flatten them into individual
# sub-tensors for batching: [layer0_key, layer0_value,
# layer1_key, layer1_value, ...].
npu_base_ptrs = []
cpu_base_ptrs = []
block_sizes_in_bytes = []
for npu_tensor, cpu_tensor in zip(self.npu_tensors, self.cpu_tensors):
for kv_idx in range(2): # 0=key, 1=value
npu_t = npu_tensor[kv_idx]
cpu_t = cpu_tensor[kv_idx]
npu_base_ptrs.append(npu_t.data_ptr())
cpu_base_ptrs.append(cpu_t.data_ptr())
# block size in bytes = stride of dim 0 (elements) * element size
block_sizes_in_bytes.append(npu_t.stride(0) * npu_t.element_size())
self._npu_base_ptrs = np.array(npu_base_ptrs, dtype=np.int64)
self._cpu_base_ptrs = np.array(cpu_base_ptrs, dtype=np.int64)
self._block_size_in_bytes_arr = np.array(block_sizes_in_bytes, dtype=np.int64)
# Total bytes per block across all sub-tensors (for transfer stats)
self._total_bytes_per_block = int(self._block_size_in_bytes_arr.sum())
def _get_event(self) -> torch.npu.Event:
if self._event_pool:
return self._event_pool.pop()
return torch.npu.Event(enable_timing=True)
def _recycle_event(self, event: torch.npu.Event) -> None:
self._event_pool.append(event)
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_base_ptrs = self._cpu_base_ptrs
dst_base_ptrs = self._npu_base_ptrs
src_block_size_factor = self.block_size_factor
dst_block_size_factor = 1
is_d2h = False
transfers = self._h2d_transfers
else:
assert isinstance(src_spec, GPULoadStoreSpec)
assert isinstance(dst_spec, CPULoadStoreSpec)
stream = self.d2h_stream
src_base_ptrs = self._npu_base_ptrs
dst_base_ptrs = self._cpu_base_ptrs
src_block_size_factor = 1
dst_block_size_factor = self.block_size_factor
is_d2h = True
transfers = self._d2h_transfers
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
# Expand block IDs into sub-block IDs
src_block_ids = np.empty(src_sub_block_count, dtype=np.int64)
dst_block_ids = np.empty(src_sub_block_count, dtype=np.int64)
expand_block_ids(src_blocks, src_block_size_factor, src_block_ids)
expand_block_ids(
dst_blocks,
dst_block_size_factor,
dst_block_ids,
skip_count=dst_sub_blocks_to_skip,
)
# Build flat pointer arrays for all sub-tensors × all block pairs.
# sub-tensors = [layer0_key, layer0_value, layer1_key, layer1_value, ...]
# Fully vectorized via numpy broadcasting (no Python loop).
num_pairs = src_sub_block_count
num_sub_tensors = len(self._block_size_in_bytes_arr)
total = num_pairs * num_sub_tensors
# (num_sub_tensors, 1) + (1, num_pairs) * (num_sub_tensors, 1) -> (num_sub_tensors, num_pairs)
bsz_col = self._block_size_in_bytes_arr[:, None] # (T, 1)
all_src = (src_base_ptrs[:, None] + src_block_ids[None, :] * bsz_col).ravel()
all_dst = (dst_base_ptrs[:, None] + dst_block_ids[None, :] * bsz_col).ravel()
all_sizes = np.broadcast_to(bsz_col, (num_sub_tensors, num_pairs)).ravel().copy()
batch_src = torch.from_numpy(all_src)
batch_dst = torch.from_numpy(all_dst)
batch_sizes = torch.from_numpy(all_sizes)
start_event = self._get_event()
end_event = self._get_event()
if is_d2h:
# Wait for model computation to finish before reading NPU data
stream.wait_stream(torch.npu.current_stream())
if transfers:
# Ensure this transfer starts only after the previous one completes
last_transfer = transfers[-1]
stream.wait_event(last_transfer.end_event)
with torch.npu.stream(stream):
start_event.record(stream)
if total > 0:
direction = 0 if not is_d2h else 1
torch.ops._C_ascend.swap_blocks_batch(batch_src, batch_dst, batch_sizes, direction)
end_event.record(stream)
transfers.append(
Transfer(
job_id=job_id,
stream=stream,
start_event=start_event,
end_event=end_event,
num_bytes=src_sub_block_count * self._total_bytes_per_block,
)
)
return True
def get_finished(self) -> list[TransferResult]:
results: list[TransferResult] = []
for transfers, transfer_type in [
(self._d2h_transfers, ("NPU", "CPU")),
(self._h2d_transfers, ("CPU", "NPU")),
]:
while transfers and transfers[0].end_event.query():
transfer = transfers.popleft()
transfer_time = transfer.start_event.elapsed_time(transfer.end_event) * 1e-3
results.append(
TransferResult(
job_id=transfer.job_id,
success=True,
transfer_size=transfer.num_bytes,
transfer_time=transfer_time,
transfer_type=transfer_type,
)
)
self._recycle_event(transfer.start_event)
self._recycle_event(transfer.end_event)
return results
def wait(self, job_ids: set[int]) -> None:
"""
Wait (block) until all specified transfer jobs are completed.
"""
for transfers in (self._d2h_transfers, self._h2d_transfers):
for transfer in transfers:
if transfer.job_id in job_ids:
transfer.end_event.synchronize()