Files
sglang/python/sglang/srt/layers/attention/flashinfer_backend.py
2024-10-22 23:20:43 -07:00

667 lines
23 KiB
Python

from __future__ import annotations
"""
Support different attention backends.
Now there are two backends: FlashInfer and Triton.
FlashInfer is faster and Triton is easier to customize.
Each backend supports two operators: extend (i.e. prefill with cached prefix) and decode.
"""
from enum import Enum, auto
from typing import TYPE_CHECKING
import torch
import triton
import triton.language as tl
from sglang.global_config import global_config
from sglang.srt.layers.attention import AttentionBackend
from sglang.srt.model_executor.forward_batch_info import ForwardBatch
from sglang.srt.utils import is_flashinfer_available
if TYPE_CHECKING:
from sglang.srt.layers.radix_attention import RadixAttention
from sglang.srt.model_executor.model_runner import ModelRunner
if is_flashinfer_available():
from flashinfer import (
BatchDecodeWithPagedKVCacheWrapper,
BatchPrefillWithPagedKVCacheWrapper,
BatchPrefillWithRaggedKVCacheWrapper,
)
from flashinfer.cascade import merge_state
from flashinfer.decode import _grouped_size_compiled_for_decode_kernels
class WrapperDispatch(Enum):
SLIDING_WINDOW = auto()
CROSS_ATTENTION = auto()
class FlashInferAttnBackend(AttentionBackend):
"""Flashinfer attention kernels."""
def __init__(self, model_runner: ModelRunner):
super().__init__()
# Parse constants
if not _grouped_size_compiled_for_decode_kernels(
model_runner.model_config.num_attention_heads // model_runner.tp_size,
model_runner.model_config.get_num_kv_heads(model_runner.tp_size),
):
self.decode_use_tensor_cores = True
else:
self.decode_use_tensor_cores = False
self.max_context_len = model_runner.model_config.context_len
assert not (
model_runner.sliding_window_size is not None
and model_runner.model_config.is_encoder_decoder
), "Sliding window and cross attention are not supported together"
if model_runner.sliding_window_size is not None:
self.num_wrappers = 2
self.dispatch_reason = WrapperDispatch.SLIDING_WINDOW
elif model_runner.model_config.is_encoder_decoder:
self.num_wrappers = 2
self.dispatch_reason = WrapperDispatch.CROSS_ATTENTION
else:
self.num_wrappers = 1
self.dispatch_reason = None
# Allocate buffers
self.workspace_buffer = torch.empty(
global_config.flashinfer_workspace_size,
dtype=torch.uint8,
device=model_runner.device,
)
max_bs = model_runner.req_to_token_pool.size
self.kv_indptr = [
torch.zeros((max_bs + 1,), dtype=torch.int32, device=model_runner.device)
for _ in range(self.num_wrappers)
]
self.kv_last_page_len = torch.ones(
(max_bs,), dtype=torch.int32, device=model_runner.device
)
self.qo_indptr = [
torch.zeros((max_bs + 1,), dtype=torch.int32, device=model_runner.device)
for _ in range(self.num_wrappers)
]
# Create wrappers
# NOTE: we do not use ragged attention when there are multiple wrappers
self.prefill_wrapper_ragged = (
BatchPrefillWithRaggedKVCacheWrapper(self.workspace_buffer, "NHD")
if self.num_wrappers == 1
else None
)
# Two wrappers: one for sliding window attention and one for full attention.
# Using two wrappers is unnecessary in the current PR, but are prepared for future PRs
self.prefill_wrappers_paged = []
self.decode_wrappers = []
for _ in range(self.num_wrappers):
self.prefill_wrappers_paged.append(
BatchPrefillWithPagedKVCacheWrapper(self.workspace_buffer, "NHD")
)
self.decode_wrappers.append(
BatchDecodeWithPagedKVCacheWrapper(
self.workspace_buffer,
"NHD",
use_tensor_cores=self.decode_use_tensor_cores,
)
)
# Create indices updater
self.indices_updater_decode = FlashInferIndicesUpdaterDecode(model_runner, self)
self.indices_updater_prefill = FlashInferIndicesUpdaterPrefill(
model_runner, self
)
# Other metadata
self.forward_metadata = None
self.cuda_graph_metadata = {}
def init_forward_metadata(self, forward_batch: ForwardBatch):
if forward_batch.forward_mode.is_decode():
self.indices_updater_decode.update(
forward_batch.req_pool_indices,
forward_batch.seq_lens,
forward_batch.seq_lens_sum,
decode_wrappers=None,
encoder_lens=forward_batch.encoder_lens,
)
self.forward_metadata = (self.decode_wrappers,)
else:
prefix_lens = forward_batch.extend_prefix_lens
# Some heuristics to check whether to use ragged forward
use_ragged = False
if forward_batch.extend_num_tokens >= 4096 and self.num_wrappers == 1:
use_ragged = True
extend_no_prefix = not torch.any(forward_batch.extend_prefix_lens).item()
self.indices_updater_prefill.update(
forward_batch.req_pool_indices,
forward_batch.seq_lens,
prefix_lens,
use_ragged=use_ragged,
encoder_lens=forward_batch.encoder_lens,
)
self.forward_metadata = (use_ragged, extend_no_prefix)
def init_cuda_graph_state(self, max_bs: int):
cuda_graph_kv_indices = torch.zeros(
(max_bs * self.max_context_len,),
dtype=torch.int32,
device="cuda",
)
self.cuda_graph_kv_indices = [cuda_graph_kv_indices] + [
cuda_graph_kv_indices.clone() for _ in range(self.num_wrappers - 1)
]
def init_forward_metadata_capture_cuda_graph(
self,
bs: int,
req_pool_indices: torch.Tensor,
seq_lens: torch.Tensor,
encoder_lens: torch.Tensor = None,
):
decode_wrappers = []
for i in range(self.num_wrappers):
decode_wrappers.append(
BatchDecodeWithPagedKVCacheWrapper(
self.workspace_buffer,
"NHD",
use_cuda_graph=True,
use_tensor_cores=self.decode_use_tensor_cores,
paged_kv_indptr_buffer=self.kv_indptr[i][: bs + 1],
paged_kv_indices_buffer=self.cuda_graph_kv_indices[i],
paged_kv_last_page_len_buffer=self.kv_last_page_len[:bs],
)
)
seq_lens_sum = seq_lens.sum().item()
self.indices_updater_decode.update(
req_pool_indices,
seq_lens,
seq_lens_sum,
decode_wrappers=decode_wrappers,
encoder_lens=encoder_lens,
)
self.cuda_graph_metadata[bs] = decode_wrappers
self.forward_metadata = (decode_wrappers,)
def init_forward_metadata_replay_cuda_graph(
self,
bs: int,
req_pool_indices: torch.Tensor,
seq_lens: torch.Tensor,
seq_lens_sum: int,
encoder_lens: torch.Tensor = None,
):
self.indices_updater_decode.update(
req_pool_indices[:bs],
seq_lens[:bs],
seq_lens_sum,
decode_wrappers=self.cuda_graph_metadata[bs],
encoder_lens=encoder_lens[:bs] if encoder_lens is not None else None,
)
def get_cuda_graph_seq_len_fill_value(self):
return 0
def forward_extend(
self, q, k, v, layer: RadixAttention, forward_batch: ForwardBatch
):
prefill_wrapper_paged = self.prefill_wrappers_paged[
self._get_wrapper_idx(layer)
]
use_ragged, extend_no_prefix = self.forward_metadata
cache_loc = (
forward_batch.out_cache_loc
if not layer.is_cross_attention
else forward_batch.encoder_out_cache_loc
)
if not use_ragged:
if k is not None:
assert v is not None
forward_batch.token_to_kv_pool.set_kv_buffer(layer, cache_loc, k, v)
o = prefill_wrapper_paged.forward(
q.contiguous().view(-1, layer.tp_q_head_num, layer.head_dim),
forward_batch.token_to_kv_pool.get_kv_buffer(layer.layer_id),
causal=not layer.is_cross_attention,
sm_scale=layer.scaling,
window_left=layer.sliding_window_size,
logits_soft_cap=layer.logit_cap,
)
else:
o1, s1 = self.prefill_wrapper_ragged.forward_return_lse(
q.contiguous().view(-1, layer.tp_q_head_num, layer.head_dim),
k.contiguous().view(-1, layer.tp_k_head_num, layer.head_dim),
v.contiguous().view(-1, layer.tp_v_head_num, layer.head_dim),
causal=True,
sm_scale=layer.scaling,
logits_soft_cap=layer.logit_cap,
)
if extend_no_prefix:
o = o1
else:
o2, s2 = prefill_wrapper_paged.forward_return_lse(
q.contiguous().view(-1, layer.tp_q_head_num, layer.head_dim),
forward_batch.token_to_kv_pool.get_kv_buffer(layer.layer_id),
causal=False,
sm_scale=layer.scaling,
logits_soft_cap=layer.logit_cap,
)
o, _ = merge_state(o1, s1, o2, s2)
forward_batch.token_to_kv_pool.set_kv_buffer(layer, cache_loc, k, v)
return o.view(-1, layer.tp_q_head_num * layer.head_dim)
def forward_decode(
self, q, k, v, layer: RadixAttention, forward_batch: ForwardBatch
):
decode_wrapper = self.forward_metadata[0][self._get_wrapper_idx(layer)]
cache_loc = (
forward_batch.out_cache_loc
if not layer.is_cross_attention
else forward_batch.encoder_out_cache_loc
)
if k is not None:
assert v is not None
forward_batch.token_to_kv_pool.set_kv_buffer(layer, cache_loc, k, v)
o = decode_wrapper.forward(
q.contiguous().view(-1, layer.tp_q_head_num, layer.head_dim),
forward_batch.token_to_kv_pool.get_kv_buffer(layer.layer_id),
sm_scale=layer.scaling,
logits_soft_cap=layer.logit_cap,
)
return o.view(-1, layer.tp_q_head_num * layer.head_dim)
def _get_wrapper_idx(self, layer: RadixAttention):
if self.num_wrappers == 1:
return 0
if self.dispatch_reason == WrapperDispatch.SLIDING_WINDOW:
return layer.sliding_window_size == -1
if self.dispatch_reason == WrapperDispatch.CROSS_ATTENTION:
return layer.is_cross_attention
raise ValueError(f"Unknown dispatch reason: {self.dispatch_reason}")
class FlashInferIndicesUpdaterDecode:
def __init__(self, model_runner: ModelRunner, attn_backend: AttentionBackend):
# Constants
self.num_qo_heads = (
model_runner.model_config.num_attention_heads // model_runner.tp_size
)
self.num_kv_heads = model_runner.model_config.get_num_kv_heads(
model_runner.tp_size
)
self.head_dim = model_runner.model_config.head_dim
self.data_type = model_runner.kv_cache_dtype
self.q_data_type = model_runner.dtype
self.max_context_len = model_runner.req_to_token_pool.req_to_token.size(1)
self.sliding_window_size = model_runner.sliding_window_size
self.attn_backend = attn_backend
# Buffers and wrappers
self.kv_indptr = attn_backend.kv_indptr
self.kv_last_page_len = attn_backend.kv_last_page_len
self.req_to_token = model_runner.req_to_token_pool.req_to_token
self.decode_wrappers = attn_backend.decode_wrappers
# Dispatch
if self.attn_backend.dispatch_reason == WrapperDispatch.SLIDING_WINDOW:
self.update = self.update_sliding_window
elif self.attn_backend.dispatch_reason == WrapperDispatch.CROSS_ATTENTION:
self.update = self.update_cross_attention
else:
assert self.attn_backend.num_wrappers == 1
self.update = self.update_single_wrapper
def update(
self, req_pool_indices, seq_lens, seq_lens_sum, decode_wrappers, encoder_lens
):
# Keep the signature for type checking. It will be assigned during runtime.
raise NotImplementedError()
def update_single_wrapper(
self,
req_pool_indices: torch.Tensor,
seq_lens: torch.Tensor,
seq_lens_sum: int,
decode_wrappers=None,
encoder_lens=None,
):
decode_wrappers = decode_wrappers or self.decode_wrappers
self.call_begin_forward(
decode_wrappers[0],
req_pool_indices,
seq_lens,
seq_lens_sum,
self.kv_indptr[0],
None,
)
def update_sliding_window(
self,
req_pool_indices: torch.Tensor,
seq_lens: torch.Tensor,
seq_lens_sum: int,
decode_wrappers=None,
encoder_lens=None,
):
decode_wrappers = decode_wrappers or self.decode_wrappers
for wrapper_id in range(2):
if wrapper_id == 0:
# Sliding window attention
paged_kernel_lens_tmp = torch.minimum( # TODO: replace this with clamp
seq_lens,
torch.tensor(self.sliding_window_size + 1),
)
paged_kernel_lens_sum_tmp = paged_kernel_lens_tmp.sum().item()
kv_start_idx_tmp = seq_lens - paged_kernel_lens_tmp
else:
# Full attention
paged_kernel_lens_tmp = seq_lens
paged_kernel_lens_sum_tmp = seq_lens_sum
kv_start_idx_tmp = None
self.call_begin_forward(
decode_wrappers[wrapper_id],
req_pool_indices,
paged_kernel_lens_tmp,
paged_kernel_lens_sum_tmp,
self.kv_indptr[wrapper_id],
kv_start_idx_tmp,
)
def update_cross_attention(
self,
req_pool_indices,
seq_lens,
seq_lens_sum,
decode_wrappers=None,
encoder_lens=None,
):
decode_wrappers = decode_wrappers or self.decode_wrappers
for wrapper_id in range(2):
if wrapper_id == 0:
# Normal attention
paged_kernel_lens = seq_lens
kv_start_idx = encoder_lens
else:
# Cross attention
paged_kernel_lens = encoder_lens
kv_start_idx = torch.zeros_like(encoder_lens)
seq_lens_sum = encoder_lens.sum().item()
self.call_begin_forward(
decode_wrappers[wrapper_id],
req_pool_indices,
paged_kernel_lens,
seq_lens_sum,
self.kv_indptr[wrapper_id],
kv_start_idx,
)
def call_begin_forward(
self,
wrapper,
req_pool_indices,
paged_kernel_lens,
paged_kernel_lens_sum,
kv_indptr,
kv_start_idx,
):
bs = len(req_pool_indices)
kv_indptr[1 : bs + 1] = torch.cumsum(paged_kernel_lens, dim=0)
kv_indptr = kv_indptr[: bs + 1]
kv_indices = torch.empty(
paged_kernel_lens_sum, dtype=torch.int32, device="cuda"
)
create_flashinfer_kv_indices_triton[(bs,)](
self.req_to_token,
req_pool_indices,
paged_kernel_lens,
kv_indptr,
kv_start_idx,
kv_indices,
self.max_context_len,
)
wrapper.end_forward()
wrapper.begin_forward(
kv_indptr,
kv_indices,
self.kv_last_page_len[:bs],
self.num_qo_heads,
self.num_kv_heads,
self.head_dim,
1,
data_type=self.data_type,
q_data_type=self.q_data_type,
)
class FlashInferIndicesUpdaterPrefill:
def __init__(self, model_runner: ModelRunner, attn_backend: AttentionBackend):
# Constants
self.num_qo_heads = (
model_runner.model_config.num_attention_heads // model_runner.tp_size
)
self.num_kv_heads = model_runner.model_config.get_num_kv_heads(
model_runner.tp_size
)
self.head_dim = model_runner.model_config.head_dim
self.data_type = model_runner.kv_cache_dtype
self.q_data_type = model_runner.dtype
self.max_context_len = model_runner.req_to_token_pool.req_to_token.size(1)
self.sliding_window_size = model_runner.sliding_window_size
self.attn_backend = attn_backend
# Buffers and wrappers
self.kv_indptr = attn_backend.kv_indptr
self.kv_last_page_len = attn_backend.kv_last_page_len
self.qo_indptr = attn_backend.qo_indptr
self.req_to_token = model_runner.req_to_token_pool.req_to_token
self.wrapper_ragged = attn_backend.prefill_wrapper_ragged
self.wrappers_paged = attn_backend.prefill_wrappers_paged
# Dispatch
if self.attn_backend.dispatch_reason == WrapperDispatch.SLIDING_WINDOW:
self.update = self.update_sliding_window
elif self.attn_backend.dispatch_reason == WrapperDispatch.CROSS_ATTENTION:
self.update = self.update_cross_attention
else:
assert self.attn_backend.num_wrappers == 1
self.update = self.update_single_wrapper
def update(self, req_pool_indices, seq_lens, prefix_lens, use_ragged, encoder_lens):
# Keep the signature for type checking. It will be assigned during runtime.
raise NotImplementedError()
def update_single_wrapper(
self, req_pool_indices, seq_lens, prefix_lens, use_ragged, encoder_lens
):
if use_ragged:
paged_kernel_lens = prefix_lens
else:
paged_kernel_lens = seq_lens
self.call_begin_forward(
self.wrapper_ragged,
self.wrappers_paged[0],
req_pool_indices,
paged_kernel_lens,
seq_lens,
prefix_lens,
None,
self.kv_indptr[0],
self.qo_indptr[0],
use_ragged,
)
def update_sliding_window(
self, req_pool_indices, seq_lens, prefix_lens, use_ragged, encoder_lens
):
for wrapper_id in range(2):
if wrapper_id == 0:
# window attention use paged only
paged_kernel_lens = torch.minimum(
seq_lens,
torch.tensor(self.sliding_window_size) + seq_lens - prefix_lens,
)
else:
# full attention
paged_kernel_lens = seq_lens
kv_start_idx = seq_lens - paged_kernel_lens
self.call_begin_forward(
self.wrapper_ragged,
self.wrappers_paged[wrapper_id],
req_pool_indices,
paged_kernel_lens,
seq_lens,
prefix_lens,
kv_start_idx,
self.kv_indptr[wrapper_id],
self.qo_indptr[wrapper_id],
use_ragged,
)
def update_cross_attention(
self, req_pool_indices, seq_lens, prefix_lens, use_ragged, encoder_lens
):
for wrapper_id in range(2):
if wrapper_id == 0:
# normal attention
paged_kernel_lens = seq_lens
kv_start_idx = encoder_lens
else:
# cross attention
paged_kernel_lens = encoder_lens
kv_start_idx = torch.zeros_like(encoder_lens)
self.call_begin_forward(
self.wrapper_ragged,
self.wrappers_paged[wrapper_id],
req_pool_indices,
paged_kernel_lens,
seq_lens,
prefix_lens,
kv_start_idx,
self.kv_indptr[wrapper_id],
self.qo_indptr[wrapper_id],
use_ragged,
)
def call_begin_forward(
self,
wrapper_ragged,
wrapper_paged,
req_pool_indices,
paged_kernel_lens,
seq_lens,
prefix_lens,
kv_start_idx,
kv_indptr,
qo_indptr,
use_ragged,
):
bs = len(req_pool_indices)
kv_indptr[1 : bs + 1] = torch.cumsum(paged_kernel_lens, dim=0)
kv_indptr = kv_indptr[: bs + 1]
kv_indices = torch.empty(kv_indptr[-1], dtype=torch.int32, device="cuda")
create_flashinfer_kv_indices_triton[(bs,)](
self.req_to_token,
req_pool_indices,
paged_kernel_lens,
kv_indptr,
kv_start_idx,
kv_indices,
self.max_context_len,
)
qo_indptr[1 : bs + 1] = torch.cumsum(seq_lens - prefix_lens, dim=0)
qo_indptr = qo_indptr[: bs + 1]
# extend part
if use_ragged:
wrapper_ragged.end_forward()
wrapper_ragged.begin_forward(
qo_indptr,
qo_indptr,
self.num_qo_heads,
self.num_kv_heads,
self.head_dim,
)
# cached part
wrapper_paged.end_forward()
wrapper_paged.begin_forward(
qo_indptr,
kv_indptr,
kv_indices,
self.kv_last_page_len[:bs],
self.num_qo_heads,
self.num_kv_heads,
self.head_dim,
1,
)
@triton.jit
def create_flashinfer_kv_indices_triton(
req_to_token_ptr, # [max_batch, max_context_len]
req_pool_indices_ptr,
page_kernel_lens_ptr,
kv_indptr,
kv_start_idx,
kv_indices_ptr,
max_context_len: tl.constexpr,
):
BLOCK_SIZE: tl.constexpr = 512
pid = tl.program_id(axis=0)
req_pool_index = tl.load(req_pool_indices_ptr + pid)
kv_indices_offset = tl.load(kv_indptr + pid)
kv_start = 0
kv_end = 0
if kv_start_idx:
kv_start = tl.load(kv_start_idx + pid).to(tl.int32)
kv_end = kv_start
kv_end += tl.load(page_kernel_lens_ptr + pid).to(tl.int32)
req_to_token_ptr += req_pool_index * max_context_len
kv_indices_ptr += kv_indices_offset
ld_offset = kv_start + tl.arange(0, BLOCK_SIZE)
st_offset = tl.arange(0, BLOCK_SIZE)
num_loop = tl.cdiv(kv_end - kv_start, BLOCK_SIZE)
for _ in range(num_loop):
mask = ld_offset < kv_end
data = tl.load(req_to_token_ptr + ld_offset, mask=mask)
tl.store(kv_indices_ptr + st_offset, data, mask=mask)
ld_offset += BLOCK_SIZE
st_offset += BLOCK_SIZE