Files
BGfilter/bgfilter/service.py
T
lhk229 c748fc22a4 Pipeline concurrent requests over a shared GPU with a narrowed lock
The single asyncio lock serialized the whole request (chroma -> seg ->
trimap -> ViTMatte -> cross-check -> foreground -> despill), so the GPU
sat idle ~70-80% of each request while the CPU stages ran. Replace it
with a thread pool that runs several requests concurrently, and move the
mutex down to just the GPU forwards: when one request steps off the GPU
to do CPU work, another steps on, keeping the device fed.

Two opt-in env knobs, both defaulting to the old strictly-serial
behaviour:
  * BGFILTER_CPU_WORKERS (pool size) attacks the CPU-bound regime -- with
    cross-check off, throughput went 0.91 -> 1.67 req/s (1.84x) at pool=8
    on a 4080S, vs a mere +6% from a second worker process, at half the
    VRAM (one model copy).
  * BGFILTER_GPU_CONCURRENCY caps how many forwards may co-schedule on the
    SMs. batch-1 underfills the GPU, so =2 recovers the SM overlap a lock
    forgoes: cross-check on went 0.83 -> 1.01 req/s, beating two worker
    processes (0.92) with one model copy (~19 GB vs 24 GB).

The CLI/single-thread path passes no lock and uses a nullcontext, so it
stays allocation- and contention-free. Concurrent output verified
identical (10x same-frame -> one hash). A per-worker admission semaphore
bounds in-flight decoded images to the pool size.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-07-14 12:47:50 +00:00

196 lines
8.2 KiB
Python

from __future__ import annotations
import logging
import os
import threading
from dataclasses import replace
import numpy as np
from .config import _SEG_MODELS, override_settings
from .memtune import release_freed_memory
from .pipeline import MattingPipeline, MattingResult
from .segmentation import BiRefNetSegmenter, make_segmenter
from .settings import PipelineSettings, SegmentationSettings
from .vitmatte_infer import ViTMatteRunner
logger = logging.getLogger("bgfilter.service")
# HTTP-facing seg_model values, in preference order (first = default).
SEG_MODELS: tuple[str, ...] = tuple(_SEG_MODELS)
class PipelineManager:
"""Long-lived holder of the matting models.
ViTMatte is the matting model shared by both segmentation backends, so it is
loaded once and reused. Each segmentation backend is lazily loaded once on
first use and cached by name. Per-request parameters (``screen_color``,
``seg_model``, ``cross_check``, ``chroma``) never trigger a model reload --
they only re-parametrise the pipeline over already-cached (or first-time-
loaded, then cached) models. ``chroma=False`` selects non-flat/complex
background mode (no colour key); ``screen_color`` is then unused.
"""
def __init__(self, base_settings: PipelineSettings, preload: bool = True):
self._base = base_settings
self._runner: ViTMatteRunner | None = None
self._segmenters: dict[str, object] = {}
self._cross_checker: BiRefNetSegmenter | None = None
self._load_lock = threading.Lock()
# Caps how many concurrent requests may be inside a GPU forward at once
# (the app may run several process() calls on a thread pool). Shared by every
# pipeline this manager builds. =1 (default) makes the device strictly
# single-stream; >1 lets that many forwards overlap so batch-1 kernels that
# underfill the SMs can co-schedule (higher GPU-bound throughput, but the
# concurrent activations multiply GPU memory). Uncontended when CPU_WORKERS=1.
gpu_conc = max(1, int(os.environ.get("BGFILTER_GPU_CONCURRENCY", "1")))
self._gpu_lock = threading.Lock() if gpu_conc == 1 else threading.BoundedSemaphore(gpu_conc)
if preload:
if base_settings.model.matting_method == "vitmatte":
self._get_runner()
# Cross-check is default behaviour, so its HR-matting model is part of
# the warm set. With reuse-as-seg on the birefnet backend that same
# forward also serves as the seg mask, so the primary segmenter is
# never used on the default path -- only preload it when reuse won't
# cover segmentation (reuse off, or a non-birefnet default backend).
if base_settings.cross_check.enabled:
self._get_cross_checker()
reuse_covers_seg = (
base_settings.cross_check.enabled
and base_settings.cross_check.reuse_as_seg
and base_settings.segmentation.backend == "birefnet"
)
if base_settings.segmentation.enabled and not reuse_covers_seg:
self._get_segmenter(base_settings.segmentation.backend)
@property
def default_seg_model(self) -> str:
return self._base.segmentation.backend
@property
def device(self) -> str:
return self._base.model.device
@property
def cross_check_enabled(self) -> bool:
return self._base.cross_check.enabled
def effective_cross_check(self, requested: bool | None) -> bool:
"""Resolve the cross-check state for a request, honoring the lane lock.
When ``cross_check.lock`` is set (e.g. the cpu-fast lane) the base default
is authoritative and a per-request override is ignored -- so a locked
off-lane never loads the HR-matting model or risks an OOM, and never errors
on a ``cross_check=on`` request. Otherwise the request value wins when
given, else the base default applies.
"""
base = self._base.cross_check
if base.lock:
return base.enabled
return requested if requested is not None else base.enabled
def _get_runner(self) -> ViTMatteRunner:
if self._runner is None:
with self._load_lock:
if self._runner is None:
logger.info(
"loading ViTMatte: model=%s device=%s",
self._base.model.model_name,
self._base.model.device,
)
self._runner = ViTMatteRunner(self._base.model)
return self._runner
def _get_segmenter(self, backend: str):
seg = self._segmenters.get(backend)
if seg is None:
with self._load_lock:
seg = self._segmenters.get(backend)
if seg is None:
seg_settings = replace(
self._base.segmentation,
backend=backend,
model_name=_SEG_MODELS[backend],
)
logger.info(
"loading segmenter: backend=%s model=%s device=%s",
backend,
seg_settings.model_name,
seg_settings.device,
)
seg = make_segmenter(seg_settings)
self._segmenters[backend] = seg
return seg
def _get_cross_checker(self) -> BiRefNetSegmenter:
# The cross-check model depends only on base settings (never on per-request
# params), so one shared instance serves all requests.
if self._cross_checker is None:
with self._load_lock:
if self._cross_checker is None:
check = self._base.cross_check
logger.info(
"loading cross-check model: model=%s device=%s",
check.model_name,
self._base.segmentation.device,
)
self._cross_checker = BiRefNetSegmenter(
SegmentationSettings(
model_name=check.model_name,
device=self._base.segmentation.device,
input_size=check.input_size,
precision=check.precision,
)
)
return self._cross_checker
def process(
self,
rgb: np.ndarray,
*,
screen_color: str | None,
seg_model: str,
cross_check: bool | None = None,
chroma: bool | None = None,
) -> MattingResult:
if seg_model not in _SEG_MODELS:
raise ValueError(f"invalid seg_model '{seg_model}'")
settings = override_settings(
self._base,
screen_color=screen_color,
seg_backend=seg_model,
# None leaves the base default; False selects non-flat/complex mode.
chroma=chroma,
# Honor the lane lock: a locked lane ignores the per-request override
# (a cpu-fast box never runs cross-check, even on cross_check=on).
cross_check=self.effective_cross_check(cross_check),
)
runner = (
self._get_runner()
if settings.model.matting_method == "vitmatte"
else None
)
segmenter = (
self._get_segmenter(seg_model) if settings.segmentation.enabled else None
)
cross_checker = (
self._get_cross_checker() if settings.cross_check.enabled else None
)
pipeline = MattingPipeline(
settings,
runner=runner,
segmenter=segmenter,
cross_checker=cross_checker,
gpu_lock=self._gpu_lock,
)
try:
return pipeline.run_rgb(rgb)
finally:
# Return this request's large freed activations to the OS so RSS does
# not ratchet up across requests in the long-lived service process.
# Hold the GPU lock: empty_cache must not race a concurrent request's
# in-flight allocations on the same device.
with self._gpu_lock:
release_freed_memory()