Move breakable CUDA graph back into model_executor/runner_backend_utils (#30586)

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>
This commit is contained in:
Yuwei An
2026-07-09 14:19:16 +08:00
committed by GitHub
co-authored by Claude Fable 5
parent 1c9eb6bb0b
commit 0562ccb1a8
11 changed files with 491 additions and 584 deletions
@@ -0,0 +1,31 @@
"""Replay-token tracking for diffusion BCG replays.
The SRT BCG core does not stamp replays; the diffusion runner sets a fresh
token around each graph replay so replay-local caches (e.g. varlen attention
mask metadata in ``DynamicVarlenMaskMeta``) can be rebuilt once per replay
while still being reused across the break points of that same replay.
``get_current_replay_token`` returns ``None`` outside a replay (including
during capture).
"""
import itertools
from contextlib import contextmanager
from contextvars import ContextVar
_current_replay_token_var: ContextVar[int | None] = ContextVar(
"mm_bcg_replay_token", default=None
)
_replay_token_counter = itertools.count(1)
def get_current_replay_token() -> int | None:
return _current_replay_token_var.get()
@contextmanager
def replay_token_scope():
token = _current_replay_token_var.set(next(_replay_token_counter))
try:
yield
finally:
_current_replay_token_var.reset(token)
@@ -36,6 +36,9 @@ from typing import Any
import torch
import torch.nn as nn
from sglang.multimodal_gen.runtime.breakable_cuda_graph.replay_token import (
replay_token_scope,
)
from sglang.srt.model_executor.runner_backend_utils.breakable_cuda_graph.breakable_cuda_graph import (
BreakableCUDAGraph,
BreakableCUDAGraphCapture,
@@ -317,7 +320,8 @@ class BaseBreakableCudaGraphRunner:
return self.transformer(**kwargs)
for buf, live in zip(entry.static_leaves, live_leaves):
buf.copy_(live, non_blocking=True)
entry.graph.replay()
with replay_token_scope():
entry.graph.replay()
# Clone so the caller can hold the result across the next replay / the
# other CFG branch (which shares this static output buffer when shapes
# match). The clone is one cheap DtoD copy relative to the full DiT.
@@ -17,6 +17,9 @@ from sglang.jit_kernel.diffusion.triton.varlen_pack_pad import (
fused_scatter_to_padded,
)
from sglang.jit_kernel.flash_attention import flash_attn_varlen_func
from sglang.multimodal_gen.runtime.breakable_cuda_graph.replay_token import (
get_current_replay_token,
)
from sglang.multimodal_gen.runtime.distributed.communication_op import (
sequence_model_parallel_all_gather,
sequence_model_parallel_all_to_all_4D,
@@ -53,9 +56,8 @@ from sglang.multimodal_gen.runtime.managers.forward_context import (
)
from sglang.multimodal_gen.runtime.platforms import AttentionBackendEnum
from sglang.multimodal_gen.utils import get_compute_dtype
from sglang.srt.breakable_cuda_graph import (
from sglang.srt.model_executor.runner_backend_utils.breakable_cuda_graph import (
eager_on_graph,
get_current_replay_token,
is_in_breakable_cuda_graph,
)
@@ -1177,6 +1179,24 @@ class USPAttention(nn.Module):
return torch.cat([out_shard, out_rep], dim=1)
class _BCGBoxedTupleOutput:
"""Box a tuple-returning break-point output as tensor attributes.
``_copy_output`` copies tensors and objects-with-tensor-attributes in
place across replays but ignores tuples, so tuple-returning attention
forwards (``UlyssesAttention``) are boxed for the break point and
unboxed after.
"""
def __init__(self, values: tuple) -> None:
self.num_values = len(values)
for i, value in enumerate(values):
setattr(self, f"value_{i}", value)
def astuple(self) -> tuple:
return tuple(getattr(self, f"value_{i}") for i in range(self.num_values))
def _make_breakable_attention_forward(forward_method):
"""Wrap a DiT attention module's ``forward`` so it becomes a breakable
CUDA graph (BCG) break point.
@@ -1187,12 +1207,18 @@ def _make_breakable_attention_forward(forward_method):
cannot (or should not) be captured into a static CUDA graph. When BCG is
disabled this is a transparent pass-through to the original method.
"""
bcg_forward = eager_on_graph(True)(forward_method)
def _forward_boxing_tuples(*args, **kwargs):
out = forward_method(*args, **kwargs)
return _BCGBoxedTupleOutput(out) if isinstance(out, tuple) else out
bcg_forward = eager_on_graph(True)(_forward_boxing_tuples)
@functools.wraps(forward_method)
def forward(self, *args, **kwargs):
if is_in_breakable_cuda_graph():
return bcg_forward(self, *args, **kwargs)
out = bcg_forward(self, *args, **kwargs)
return out.astuple() if isinstance(out, _BCGBoxedTupleOutput) else out
return forward_method(self, *args, **kwargs)
return forward
@@ -1,44 +0,0 @@
# Copyright 2023-2026 SGLang Team
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
# ==============================================================================
"""Model-agnostic breakable CUDA graph (BCG) primitives.
Shared by the LLM runtime (``sglang.srt.model_executor``) and the diffusion
runtime (``sglang.multimodal_gen``). Capture a forward region as a sequence of
``torch.cuda.CUDAGraph`` segments separated by eager break points inserted via
:func:`eager_on_graph`-decorated callables.
"""
from sglang.srt.breakable_cuda_graph.breakable_cuda_graph import (
BreakableCUDAGraph,
BreakableCUDAGraphCapture,
break_graph,
eager_on_graph,
get_current_replay_token,
)
from sglang.srt.breakable_cuda_graph.context import (
BCG_FAILURE_HINT,
enable_breakable_cuda_graph,
is_in_breakable_cuda_graph,
)
__all__ = [
"BreakableCUDAGraph",
"BreakableCUDAGraphCapture",
"break_graph",
"eager_on_graph",
"get_current_replay_token",
"BCG_FAILURE_HINT",
"enable_breakable_cuda_graph",
"is_in_breakable_cuda_graph",
]
@@ -1,389 +0,0 @@
# Copyright 2023-2026 SGLang Team
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
# ==============================================================================
"""Breakable CUDA Graph: capture a region as a sequence of
``torch.cuda.CUDAGraph`` segments separated by eager break points.
Each segment is a real ``torch.cuda.CUDAGraph``. Its destructor calls
``releasePool`` on the shared mempool, so the pool's ``use_count`` tracks how
many segments are alive; the pool stays pinned as long as any segment graph
is alive. This lets ``weak_ref_tensor`` views of intermediate pool-allocated
tensors remain valid across replays — we don't need Python-managed bridge
buffers to keep break-point tensors at stable addresses.
This module is model-agnostic. The LLM runtime (``sglang.srt``) breaks at
radix-attention / mamba; the diffusion runtime (``sglang.multimodal_gen``)
breaks at the DiT attention modules, where sequence-parallel all-to-all and
dynamic/varlen/sparse attention kernels must run eagerly between captured
segments. Break-point callables may return a single tensor, a tuple/list of
tensors, or an object/dict of tensors — see :func:`_copy_output`.
"""
import itertools
import logging
import threading
from contextvars import ContextVar
from typing import Any, Callable
import torch
try:
from cuda.bindings import runtime as rt
except ImportError:
rt = None
from sglang.srt.breakable_cuda_graph.cuda_utils import checkCudaErrors
from sglang.srt.utils import is_hip
logger = logging.getLogger(__name__)
__all__ = [
"eager_on_graph",
"BreakableCUDAGraph",
"BreakableCUDAGraphCapture",
"break_graph",
"get_current_replay_token",
]
def _check_cuda_bindings():
if rt is None:
raise ImportError(
"Breakable CUDA graph requires the 'cuda-python' package. "
"Install it with: pip install cuda-python"
)
# Active BreakableCUDAGraphCapture context for the currently-capturing thread.
# eager_on_graph's wrapper uses this to split the current torch.cuda.CUDAGraph
# at break points.
_current_capture_var: ContextVar["BreakableCUDAGraphCapture | None"] = ContextVar(
"current_capture", default=None
)
_current_stream_var: ContextVar[torch.cuda.Stream | None] = ContextVar(
"current_stream", default=None
)
_current_replay_token_var: ContextVar[int | None] = ContextVar(
"current_replay_token", default=None
)
_forked_streams_var: ContextVar[set[torch.cuda.Stream] | None] = ContextVar(
"forked_streams", default=None
)
_replay_token_counter = itertools.count(1)
def get_current_stream(device: torch.device | None = None) -> torch.cuda.Stream:
stream = _current_stream_var.get()
if stream is None:
return torch.cuda.current_stream(device)
return stream
def get_current_replay_token() -> int | None:
"""Return a unique token for the current BCG replay, or ``None``.
Eager break-point code can use this to cache metadata within a single replay
while still rebuilding it for the next replay when static buffers change.
This was added for diffusion model adaptation, where Qwen Image rebuilds
replay-local varlen attention metadata from the current prompt mask.
"""
return _current_replay_token_var.get()
def _capture_status(stream_ptr: int) -> "rt.cudaStreamCaptureStatus":
_check_cuda_bindings()
status, *_ = checkCudaErrors(rt.cudaStreamGetCaptureInfo(stream_ptr))
return status
def _is_stream_capturing(stream: torch.cuda.Stream) -> bool:
# On ROCm/HIP, cuda-python is unavailable, so use the portable torch API
# (which maps to the HIP runtime). On NVIDIA, keep querying the CUDA runtime
# directly via cuda-python: torch.cuda.is_current_stream_capturing() has
# proven unreliable there, so we preserve the original behavior.
if is_hip():
with torch.cuda.stream(stream):
return torch.cuda.is_current_stream_capturing()
return (
_capture_status(stream.cuda_stream)
== rt.cudaStreamCaptureStatus.cudaStreamCaptureStatusActive
)
# Hook torch.cuda.Stream.wait_stream to track side-stream forks/joins that happen
# during breakable capture. We need this because capture_end() on a torch
# CUDAGraph fails if there are still side streams participating in the capture
# — so before ending each segment we auto-join any forked-but-not-rejoined streams.
_original_wait_stream: Callable | None = None
_hook_lock = threading.Lock()
_hook_refcount = 0
def _hooked_wait_stream(self: torch.cuda.Stream, other: torch.cuda.Stream):
assert _original_wait_stream is not None
forked = _forked_streams_var.get()
if forked is None:
_original_wait_stream(self, other)
return
capturing = _current_stream_var.get()
if capturing is None:
_original_wait_stream(self, other)
return
cap_ptr = capturing.cuda_stream
is_self_cap = self is capturing or self.cuda_stream == cap_ptr
is_other_cap = other is capturing or other.cuda_stream == cap_ptr
if is_self_cap and not is_other_cap:
if not _is_stream_capturing(other):
return
_original_wait_stream(self, other)
forked.discard(other)
elif is_other_cap and not is_self_cap:
_original_wait_stream(self, other)
forked.add(self)
else:
_original_wait_stream(self, other)
def _install_wait_stream_hook():
global _original_wait_stream, _hook_refcount
with _hook_lock:
if _hook_refcount == 0:
_original_wait_stream = torch.cuda.Stream.wait_stream
torch.cuda.Stream.wait_stream = _hooked_wait_stream # type: ignore[assignment]
_hook_refcount += 1
def _uninstall_wait_stream_hook():
global _original_wait_stream, _hook_refcount
with _hook_lock:
_hook_refcount -= 1
if _hook_refcount == 0:
assert _original_wait_stream is not None, "wait_stream hook not installed"
torch.cuda.Stream.wait_stream = _original_wait_stream # type: ignore[assignment]
_original_wait_stream = None
def _weak_ref_if_tensor(x):
"""Return a weak-ref tensor view (shared storage, no refcount) for tensors;
recurse into tuples/lists; pass-through for everything else. Weak-ref'ing
captured args/outputs lets the shared mempool reclaim per-layer
intermediates between segments — storage stays alive for each segment
CUDAGraph's lifetime via its pool use_count.
``weak_ref_tensors`` is imported lazily: the module hard-raises on
non-CUDA/NPU platforms, and we only reach this code during an active
BCG capture (which can't happen on CPU-only runners anyway)."""
if torch.is_tensor(x):
from sglang.srt.compilation.weak_ref_tensor import weak_ref_tensors
return weak_ref_tensors(x)
if isinstance(x, tuple):
return tuple(_weak_ref_if_tensor(e) for e in x)
if isinstance(x, list):
return [_weak_ref_if_tensor(e) for e in x]
return x
def _copy_output(dst: Any, src: Any) -> Any:
"""Copy src output into dst in-place where possible.
Handles plain tensors, tuples/lists of tensors, dataclass/object with
tensor attributes, and dicts of tensors. Returns dst if in-place copy
succeeded, otherwise returns src.
The in-place copy is what keeps a break point's output at a stable address
across replays: ``dst`` is the weak-ref'd capture-time output (pinned by the
segment mempool), and the downstream captured segment reads from that
address, so each replay must write fresh data back into ``dst`` rather than
return a freshly-allocated tensor.
"""
if torch.is_tensor(dst) and torch.is_tensor(src):
dst.copy_(src)
return dst
if (
isinstance(dst, (tuple, list))
and isinstance(src, (tuple, list))
and len(dst) == len(src)
):
copied = [_copy_output(d, s) for d, s in zip(dst, src)]
return tuple(copied) if isinstance(dst, tuple) else copied
if hasattr(dst, "__dict__") and hasattr(src, "__dict__"):
for key, src_val in src.__dict__.items():
dst_val = getattr(dst, key, None)
if torch.is_tensor(dst_val) and torch.is_tensor(src_val):
dst_val.copy_(src_val)
else:
setattr(dst, key, src_val)
return dst
if isinstance(dst, dict) and isinstance(src, dict):
for key, src_val in src.items():
dst_val = dst.get(key)
if torch.is_tensor(dst_val) and torch.is_tensor(src_val):
dst_val.copy_(src_val)
else:
dst[key] = src_val
return dst
return src
def eager_on_graph(enable: bool):
def decorator(inner: Callable):
if not enable:
return inner
def wrapper(*args, **kwargs):
capture = _current_capture_var.get()
if capture is None:
return inner(*args, **kwargs)
logger.debug("Break graph due to function: %s", inner.__name__)
# End the segment that captured up to this break point.
capture._end_current_segment()
# Run the eager function once so it allocates its outputs and
# writes real data into them.
output = inner(*args, **kwargs)
# Weak-ref the closure state. Storage lives with the segment
# CUDAGraphs' mempool pin; Python refs don't need to prevent
# pool reuse across layers.
captured_inner = inner
captured_args = tuple(_weak_ref_if_tensor(a) for a in args)
captured_kwargs = {k: _weak_ref_if_tensor(v) for k, v in kwargs.items()}
captured_output = _weak_ref_if_tensor(output)
def replay_fn():
new_out = captured_inner(*captured_args, **captured_kwargs)
return _copy_output(captured_output, new_out)
capture.cuda_graph._break_fns.append(replay_fn)
# Start a fresh CUDAGraph segment for the remainder of the forward.
capture._begin_new_segment()
return output
return wrapper
return decorator
class BreakableCUDAGraph:
"""Container holding one ``torch.cuda.CUDAGraph`` per segment plus an
eager break function between consecutive segments."""
def __init__(self) -> None:
self._segments: list[torch.cuda.CUDAGraph] = []
self._break_fns: list[Callable[[], Any]] = []
def replay(self) -> None:
stream = torch.cuda.current_stream()
stream_token = _current_stream_var.set(stream)
replay_token = _current_replay_token_var.set(next(_replay_token_counter))
try:
for i, seg in enumerate(self._segments):
seg.replay()
if i < len(self._break_fns):
self._break_fns[i]()
finally:
_current_replay_token_var.reset(replay_token)
_current_stream_var.reset(stream_token)
class BreakableCUDAGraphCapture:
"""Context manager that captures the enclosed code as one or more
``torch.cuda.CUDAGraph`` segments separated by eager break points.
Each segment shares the supplied ``pool`` (``MempoolId_t`` tuple) so
pool-allocated intermediates can be reused across segments. While any
segment is alive, its ``beginAllocateToPool`` call keeps the mempool's
``use_count`` > 0, which makes ``weak_ref_tensor`` of segment-allocated
tensors safe across subsequent replays.
"""
def __init__(
self,
cuda_graph: BreakableCUDAGraph,
pool=None,
stream: torch.cuda.Stream | None = None,
capture_error_mode: str = "global",
):
assert isinstance(
cuda_graph, BreakableCUDAGraph
), "cuda_graph must be a BreakableCUDAGraph"
self.cuda_graph = cuda_graph
self._pool = pool if pool is not None else (0, 0)
self._stream = stream
self._capture_error_mode = capture_error_mode
self._stream_ctx = None
self._capture_token = None
self._stream_token = None
self._forked_token = None
def __enter__(self):
_install_wait_stream_hook()
if self._stream is not None:
self._stream_ctx = torch.cuda.stream(self._stream)
self._stream_ctx.__enter__()
self._capture_token = _current_capture_var.set(self)
self._stream_token = _current_stream_var.set(
self._stream or torch.cuda.current_stream()
)
self._forked_token = _forked_streams_var.set(set())
self._begin_new_segment()
return self
def __exit__(self, *args: object):
try:
self._end_current_segment()
finally:
_forked_streams_var.reset(self._forked_token)
_current_stream_var.reset(self._stream_token)
_current_capture_var.reset(self._capture_token)
if self._stream_ctx is not None:
self._stream_ctx.__exit__(*args)
self._stream_ctx = None
_uninstall_wait_stream_hook()
return False
def _begin_new_segment(self) -> None:
graph = torch.cuda.CUDAGraph()
graph.capture_begin(
pool=self._pool, capture_error_mode=self._capture_error_mode
)
self.cuda_graph._segments.append(graph)
def _end_current_segment(self) -> None:
# Auto-join any side streams forked during this segment but not joined.
main_stream = get_current_stream()
forked = _forked_streams_var.get()
if forked:
assert _original_wait_stream is not None
for side in list(forked):
if _is_stream_capturing(side):
_original_wait_stream(main_stream, side)
forked.clear()
self.cuda_graph._segments[-1].capture_end()
@eager_on_graph(True)
def break_graph() -> None:
"""Insert a graph break. The @eager_on_graph decorator does the actual
segment split; this function body intentionally does nothing."""
pass
@@ -1,50 +0,0 @@
# Copyright 2023-2026 SGLang Team
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
# ==============================================================================
"""Runtime state for the breakable CUDA graph (BCG) runner.
Kept intentionally separate from ``compilation/piecewise_context_manager.py``:
BCG no longer inherits from the torch.compile-based PCG path, so its
capture/replay lifecycle is managed on its own.
This module is model-agnostic: it is shared by the LLM runtime
(``sglang.srt``) and the diffusion runtime (``sglang.multimodal_gen``).
"""
from __future__ import annotations
from contextlib import contextmanager
_in_breakable_cuda_graph = False
BCG_FAILURE_HINT = (
"1. change to tc_piecewise by --cuda-graph-backend-prefill=tc_piecewise\n"
"2. disable the prefill CUDA graph by --cuda-graph-backend-prefill=disabled\n"
"3. if it is an OOM problem, set --mem-fraction-static to a smaller value "
"(e.g., 0.8 or 0.7) or set --cuda-graph-max-bs-prefill to a smaller value "
"(e.g., 2048)\n"
)
def is_in_breakable_cuda_graph() -> bool:
return _in_breakable_cuda_graph
@contextmanager
def enable_breakable_cuda_graph():
global _in_breakable_cuda_graph
_in_breakable_cuda_graph = True
try:
yield
finally:
_in_breakable_cuda_graph = False
@@ -1,48 +0,0 @@
# Copyright 2023-2026 SGLang Team
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
# ==============================================================================
"""CUDA runtime binding utilities."""
try:
from cuda.bindings import runtime as rt
except ImportError:
rt = None
def _cudaGetErrorString(error):
if rt is None:
return "<cuda.bindings not available>"
err, msg = rt.cudaGetErrorString(error)
if err != rt.cudaError_t.cudaSuccess:
return "<unknown>"
if isinstance(msg, bytes):
return msg.decode("utf-8", "replace")
return str(msg)
def checkCudaErrors(result):
if rt is None:
raise RuntimeError(
"cuda.bindings is not available. "
"Install it with: pip install cuda-python"
)
if result[0] != rt.cudaError_t.cudaSuccess:
raise RuntimeError(
f"CUDA error {int(result[0])}({_cudaGetErrorString(result[0])})"
)
if len(result) == 1:
return None
elif len(result) == 2:
return result[1]
else:
return result[1:]
@@ -14,21 +14,8 @@ from sglang.srt.model_executor.runner_backend_utils.breakable_cuda_graph.breakab
BreakableCUDAGraphCapture,
break_graph,
eager_on_graph,
get_current_replay_token,
)
from sglang.srt.model_executor.runner_backend_utils.breakable_cuda_graph.context import ( # noqa: F401
BCG_FAILURE_HINT,
enable_breakable_cuda_graph,
is_in_breakable_cuda_graph,
)
__all__ = [
"BreakableCUDAGraph",
"BreakableCUDAGraphCapture",
"break_graph",
"eager_on_graph",
"get_current_replay_token",
"BCG_FAILURE_HINT",
"enable_breakable_cuda_graph",
"is_in_breakable_cuda_graph",
]
@@ -11,30 +11,364 @@
# See the License for the specific language governing permissions and
# limitations under the License.
# ==============================================================================
"""Backward-compatible re-export shim.
"""Breakable CUDA Graph: capture a region as a sequence of
torch.cuda.CUDAGraph segments separated by eager break points.
The breakable CUDA graph primitives moved to the model-agnostic package
:mod:`sglang.srt.breakable_cuda_graph` so the diffusion runtime
(``sglang.multimodal_gen``) can share them with the LLM runtime. This module
preserves the historical import path.
Each segment is a real torch.cuda.CUDAGraph. Its destructor calls
releasePool on the shared mempool, so the pool's use_count tracks how
many segments are alive; the pool stays pinned as long as any segment graph
is alive. This lets weak_ref_tensor views of intermediate pool-allocated
tensors remain valid across replays — we don't need Python-managed bridge
buffers to keep break-point tensors at stable addresses.
"""
from sglang.srt.breakable_cuda_graph.breakable_cuda_graph import ( # noqa: F401
BreakableCUDAGraph,
BreakableCUDAGraphCapture,
_copy_output,
break_graph,
eager_on_graph,
get_current_replay_token,
get_current_stream,
import logging
import threading
from contextvars import ContextVar
from typing import Any, Callable
import torch
try:
from cuda.bindings import runtime as rt
except ImportError:
rt = None
from sglang.srt.model_executor.runner_backend_utils.breakable_cuda_graph.cuda_utils import (
checkCudaErrors,
)
from sglang.srt.utils import is_hip
logger = logging.getLogger(__name__)
__all__ = [
"eager_on_graph",
"BreakableCUDAGraph",
"BreakableCUDAGraphCapture",
"_copy_output",
"break_graph",
"get_current_stream",
"get_current_replay_token",
]
def _check_cuda_bindings():
if rt is None:
raise ImportError(
"Breakable CUDA graph on NVIDIA requires the 'cuda-python' package. "
"Install it with: pip install cuda-python"
)
# Active BreakableCUDAGraphCapture context for the currently-capturing thread.
# eager_on_graph's wrapper uses this to split the current torch.cuda.CUDAGraph
# at break points.
_current_capture_var: ContextVar["BreakableCUDAGraphCapture | None"] = ContextVar(
"current_capture", default=None
)
_current_stream_var: ContextVar[torch.cuda.Stream | None] = ContextVar(
"current_stream", default=None
)
_forked_streams_var: ContextVar[set[torch.cuda.Stream] | None] = ContextVar(
"forked_streams", default=None
)
def get_current_stream(device: torch.device | None = None) -> torch.cuda.Stream:
stream = _current_stream_var.get()
if stream is None:
return torch.cuda.current_stream(device)
return stream
def _capture_status(stream_ptr: int) -> "rt.cudaStreamCaptureStatus":
_check_cuda_bindings()
status, *_ = checkCudaErrors(rt.cudaStreamGetCaptureInfo(stream_ptr))
return status
def _is_stream_capturing(stream: torch.cuda.Stream) -> bool:
# On ROCm/HIP, cuda-python is unavailable, so use the portable torch API
# (which maps to the HIP runtime). On NVIDIA, keep querying the CUDA runtime
# directly via cuda-python: torch.cuda.is_current_stream_capturing() has
# proven unreliable there, so we preserve the original behavior.
if is_hip():
with torch.cuda.stream(stream):
return torch.cuda.is_current_stream_capturing()
return (
_capture_status(stream.cuda_stream)
== rt.cudaStreamCaptureStatus.cudaStreamCaptureStatusActive
)
# Hook torch.cuda.Stream.wait_stream to track side-stream forks/joins that happen
# during breakable capture. We need this because capture_end() on a torch
# CUDAGraph fails if there are still side streams participating in the capture
# — so before ending each segment we auto-join any forked-but-not-rejoined streams.
_original_wait_stream: Callable | None = None
_hook_lock = threading.Lock()
_hook_refcount = 0
def _hooked_wait_stream(self: torch.cuda.Stream, other: torch.cuda.Stream):
assert _original_wait_stream is not None
forked = _forked_streams_var.get()
if forked is None:
_original_wait_stream(self, other)
return
capturing = _current_stream_var.get()
if capturing is None:
_original_wait_stream(self, other)
return
cap_ptr = capturing.cuda_stream
is_self_cap = self is capturing or self.cuda_stream == cap_ptr
is_other_cap = other is capturing or other.cuda_stream == cap_ptr
if is_self_cap and not is_other_cap:
if not _is_stream_capturing(other):
return
_original_wait_stream(self, other)
forked.discard(other)
elif is_other_cap and not is_self_cap:
_original_wait_stream(self, other)
forked.add(self)
else:
_original_wait_stream(self, other)
def _install_wait_stream_hook():
global _original_wait_stream, _hook_refcount
with _hook_lock:
if _hook_refcount == 0:
_original_wait_stream = torch.cuda.Stream.wait_stream
torch.cuda.Stream.wait_stream = _hooked_wait_stream # type: ignore[assignment]
_hook_refcount += 1
def _uninstall_wait_stream_hook():
global _original_wait_stream, _hook_refcount
with _hook_lock:
_hook_refcount -= 1
if _hook_refcount == 0:
assert _original_wait_stream is not None, "wait_stream hook not installed"
torch.cuda.Stream.wait_stream = _original_wait_stream # type: ignore[assignment]
_original_wait_stream = None
def _weak_ref_if_tensor(x):
"""Return a weak-ref tensor view (shared storage, no refcount) for tensors;
pass-through for non-tensors. Weak-ref'ing captured args lets the shared
mempool reclaim per-layer intermediates between segments — storage stays
alive for each segment CUDAGraph's lifetime via its pool use_count.
weak_ref_tensors is imported lazily because it hard-raises on
platforms without a CUDA/HIP/NPU backend; we only reach this code during
an active Breakable capture, which runs only on those backends."""
if torch.is_tensor(x):
from sglang.srt.compilation.weak_ref_tensor import weak_ref_tensors
return weak_ref_tensors(x)
return x
def _copy_output(dst: Any, src: Any) -> Any:
"""Copy src output into dst in-place where possible.
Handles plain tensors, dataclass/object with tensor attributes,
and dicts of tensors. Returns dst if in-place copy succeeded,
otherwise returns src.
"""
if torch.is_tensor(dst) and torch.is_tensor(src):
dst.copy_(src)
return dst
if hasattr(dst, "__dict__") and hasattr(src, "__dict__"):
for key, src_val in src.__dict__.items():
dst_val = getattr(dst, key, None)
if torch.is_tensor(dst_val) and torch.is_tensor(src_val):
dst_val.copy_(src_val)
else:
setattr(dst, key, src_val)
return dst
if isinstance(dst, dict) and isinstance(src, dict):
for key, src_val in src.items():
dst_val = dst.get(key)
if torch.is_tensor(dst_val) and torch.is_tensor(src_val):
dst_val.copy_(src_val)
else:
dst[key] = src_val
return dst
return src
def eager_on_graph(enable: bool):
def decorator(inner: Callable):
if not enable:
return inner
def wrapper(*args, **kwargs):
capture = _current_capture_var.get()
if capture is None:
return inner(*args, **kwargs)
logger.debug("Break graph due to function: %s", inner.__name__)
# End the segment that captured up to this break point.
capture._end_current_segment()
# Run the eager function once so it allocates its outputs and
# writes real data into them.
output = inner(*args, **kwargs)
# Weak-ref the closure state. Storage lives with the segment
# CUDAGraphs' mempool pin; Python refs don't need to prevent
# pool reuse across layers.
captured_inner = inner
captured_args = tuple(_weak_ref_if_tensor(a) for a in args)
captured_kwargs = {k: _weak_ref_if_tensor(v) for k, v in kwargs.items()}
captured_output = _weak_ref_if_tensor(output)
def replay_fn():
new_out = captured_inner(*captured_args, **captured_kwargs)
return _copy_output(captured_output, new_out)
capture.cuda_graph._break_fns.append(replay_fn)
# Start a fresh CUDAGraph segment for the remainder of the forward.
capture._begin_new_segment()
return output
return wrapper
return decorator
class BreakableCUDAGraph:
"""Container holding one torch.cuda.CUDAGraph per segment plus an
eager break function between consecutive segments."""
def __init__(self, deduped_cuda_graph=None) -> None:
self._segments: list[Any] = []
self._break_fns: list[Callable[[], Any]] = []
self._deduped_cuda_graph = deduped_cuda_graph
def replay(self) -> None:
stream = torch.cuda.current_stream()
token = _current_stream_var.set(stream)
try:
for i, seg in enumerate(self._segments):
seg.replay()
if i < len(self._break_fns):
self._break_fns[i]()
finally:
_current_stream_var.reset(token)
def _append_segment(
self, graph: torch.cuda.CUDAGraph, needs_instantiate: bool
) -> None:
if self._deduped_cuda_graph is not None:
self._segments.append(self._deduped_cuda_graph.register(graph))
return
if needs_instantiate:
graph.instantiate()
self._segments.append(graph)
class BreakableCUDAGraphCapture:
"""Context manager that captures the enclosed code as one or more
torch.cuda.CUDAGraph segments separated by eager break points.
Each segment shares the supplied pool (MempoolId_t tuple) so
pool-allocated intermediates can be reused across segments. While any
segment is alive, its beginAllocateToPool call keeps the mempool's
use_count > 0, which makes weak_ref_tensor of segment-allocated
tensors safe across subsequent replays.
"""
def __init__(
self,
cuda_graph: BreakableCUDAGraph,
pool=None,
stream: torch.cuda.Stream | None = None,
capture_error_mode: str = "global",
):
assert isinstance(
cuda_graph, BreakableCUDAGraph
), "cuda_graph must be a BreakableCUDAGraph"
self.cuda_graph = cuda_graph
self._pool = pool if pool is not None else (0, 0)
self._stream = stream
self._capture_error_mode = capture_error_mode
self._stream_ctx = None
self._capture_token = None
self._stream_token = None
self._forked_token = None
self._current_graph: torch.cuda.CUDAGraph | None = None
self._current_graph_needs_instantiate = False
def __enter__(self):
_install_wait_stream_hook()
if self._stream is not None:
self._stream_ctx = torch.cuda.stream(self._stream)
self._stream_ctx.__enter__()
self._capture_token = _current_capture_var.set(self)
self._stream_token = _current_stream_var.set(
self._stream or torch.cuda.current_stream()
)
self._forked_token = _forked_streams_var.set(set())
self._begin_new_segment()
return self
def __exit__(self, *args: object):
try:
self._end_current_segment()
finally:
_forked_streams_var.reset(self._forked_token)
_current_stream_var.reset(self._stream_token)
_current_capture_var.reset(self._capture_token)
if self._stream_ctx is not None:
self._stream_ctx.__exit__(*args)
self._stream_ctx = None
_uninstall_wait_stream_hook()
return False
def _begin_new_segment(self) -> None:
# keep_graph retains the raw graph for dedup; skip it on the plain path.
if self.cuda_graph._deduped_cuda_graph is not None:
try:
graph = torch.cuda.CUDAGraph(keep_graph=True)
self._current_graph_needs_instantiate = True
except TypeError:
graph = torch.cuda.CUDAGraph()
self._current_graph_needs_instantiate = False
else:
graph = torch.cuda.CUDAGraph()
self._current_graph_needs_instantiate = False
graph.capture_begin(
pool=self._pool, capture_error_mode=self._capture_error_mode
)
self._current_graph = graph
def _end_current_segment(self) -> None:
# Auto-join any side streams forked during this segment but not joined.
main_stream = get_current_stream()
forked = _forked_streams_var.get()
if forked:
assert _original_wait_stream is not None
for side in list(forked):
if _is_stream_capturing(side):
_original_wait_stream(main_stream, side)
forked.clear()
graph = self._current_graph
assert graph is not None
graph.capture_end()
self.cuda_graph._append_segment(graph, self._current_graph_needs_instantiate)
self._current_graph = None
self._current_graph_needs_instantiate = False
@eager_on_graph(True)
def break_graph() -> None:
"""Insert a graph break. The @eager_on_graph decorator does the actual
segment split; this function body intentionally does nothing."""
pass
@@ -11,19 +11,50 @@
# See the License for the specific language governing permissions and
# limitations under the License.
# ==============================================================================
"""Backward-compatible re-export shim for the moved BCG context helpers.
"""Runtime state for the breakable CUDA graph runner."""
See :mod:`sglang.srt.breakable_cuda_graph.context`.
"""
from __future__ import annotations
from sglang.srt.breakable_cuda_graph.context import ( # noqa: F401
BCG_FAILURE_HINT,
enable_breakable_cuda_graph,
is_in_breakable_cuda_graph,
import logging
from contextlib import contextmanager
from sglang.srt.model_executor.cuda_graph_config import Backend
from sglang.srt.model_executor.runner_backend_utils import (
PREFILL_CUDA_GRAPH_CAPTURE_FAILED_MSG,
)
__all__ = [
"BCG_FAILURE_HINT",
"enable_breakable_cuda_graph",
"is_in_breakable_cuda_graph",
]
logger = logging.getLogger(__name__)
_in_breakable_cuda_graph = False
def is_in_breakable_cuda_graph() -> bool:
return _in_breakable_cuda_graph
@contextmanager
def enable_breakable_cuda_graph():
"""Mark the enclosed scope as inside a BCG capture/replay. Any exception
raised inside is logged with the BCG-specific failure hint, then re-raised
for the caller to handle."""
global _in_breakable_cuda_graph
_in_breakable_cuda_graph = True
try:
yield
except Exception as exc:
msg = PREFILL_CUDA_GRAPH_CAPTURE_FAILED_MSG.format(
backend=Backend.BREAKABLE, suggestions=BCG_FAILURE_HINT
)
logger.error(f"{type(exc).__name__}: {exc}\n{msg}")
raise
finally:
_in_breakable_cuda_graph = False
BCG_FAILURE_HINT = (
"1. change to tc_piecewise by --cuda-graph-backend-prefill=tc_piecewise\n"
"2. disable the prefill CUDA graph by --cuda-graph-backend-prefill=disabled\n"
"3. if it is an OOM problem, set --mem-fraction-static to a smaller value "
"(e.g., 0.8 or 0.7) or set --cuda-graph-max-bs-prefill to a smaller value "
"(e.g., 2048)\n"
)
@@ -11,13 +11,38 @@
# See the License for the specific language governing permissions and
# limitations under the License.
# ==============================================================================
"""Backward-compatible re-export shim for the moved CUDA runtime utilities.
"""CUDA runtime binding utilities."""
See :mod:`sglang.srt.breakable_cuda_graph.cuda_utils`.
"""
try:
from cuda.bindings import runtime as rt
except ImportError:
rt = None
from sglang.srt.breakable_cuda_graph.cuda_utils import ( # noqa: F401
checkCudaErrors,
)
__all__ = ["checkCudaErrors"]
def _cudaGetErrorString(error):
if rt is None:
return "<cuda.bindings not available>"
err, msg = rt.cudaGetErrorString(error)
if err != rt.cudaError_t.cudaSuccess:
return "<unknown>"
if isinstance(msg, bytes):
return msg.decode("utf-8", "replace")
return str(msg)
def checkCudaErrors(result):
if rt is None:
raise RuntimeError(
"cuda.bindings is not available. "
"Install it with: pip install cuda-python"
)
if result[0] != rt.cudaError_t.cudaSuccess:
raise RuntimeError(
f"CUDA error {int(result[0])}({_cudaGetErrorString(result[0])})"
)
if len(result) == 1:
return None
elif len(result) == 2:
return result[1]
else:
return result[1:]