[Enhance] Add setup multi-processing both in train and test.

mmcls/utils/__init__.py

@@ -1,5 +1,8 @@
 # Copyright (c) OpenMMLab. All rights reserved.
 from .collect_env import collect_env
 from .logger import get_root_logger, load_json_log
+from .setup_env import setup_multi_processes
 
-__all__ = ['collect_env', 'get_root_logger', 'load_json_log']
+__all__ = [
+    'collect_env', 'get_root_logger', 'load_json_log', 'setup_multi_processes'
+]

mmcls/utils/setup_env.py

@@ -0,0 +1,47 @@
+# Copyright (c) OpenMMLab. All rights reserved.
+import os
+import platform
+import warnings
+
+import cv2
+import torch.multiprocessing as mp
+
+
+def setup_multi_processes(cfg):
+    """Setup multi-processing environment variables."""
+    # set multi-process start method as `fork` to speed up the training
+    if platform.system() != 'Windows':
+        mp_start_method = cfg.get('mp_start_method', 'fork')
+        current_method = mp.get_start_method(allow_none=True)
+        if current_method is not None and current_method != mp_start_method:
+            warnings.warn(
+                f'Multi-processing start method `{mp_start_method}` is '
+                f'different from the previous setting `{current_method}`.'
+                f'It will be force set to `{mp_start_method}`. You can change '
+                f'this behavior by changing `mp_start_method` in your config.')
+        mp.set_start_method(mp_start_method, force=True)
+
+    # disable opencv multithreading to avoid system being overloaded
+    opencv_num_threads = cfg.get('opencv_num_threads', 0)
+    cv2.setNumThreads(opencv_num_threads)
+
+    # setup OMP threads
+    # This code is referred from https://github.com/pytorch/pytorch/blob/master/torch/distributed/run.py  # noqa
+    if 'OMP_NUM_THREADS' not in os.environ and cfg.data.workers_per_gpu > 1:
+        omp_num_threads = 1
+        warnings.warn(
+            f'Setting OMP_NUM_THREADS environment variable for each process '
+            f'to be {omp_num_threads} in default, to avoid your system being '
+            f'overloaded, please further tune the variable for optimal '
+            f'performance in your application as needed.')
+        os.environ['OMP_NUM_THREADS'] = str(omp_num_threads)
+
+    # setup MKL threads
+    if 'MKL_NUM_THREADS' not in os.environ and cfg.data.workers_per_gpu > 1:
+        mkl_num_threads = 1
+        warnings.warn(
+            f'Setting MKL_NUM_THREADS environment variable for each process '
+            f'to be {mkl_num_threads} in default, to avoid your system being '
+            f'overloaded, please further tune the variable for optimal '
+            f'performance in your application as needed.')
+        os.environ['MKL_NUM_THREADS'] = str(mkl_num_threads)

setup.cfg

@@ -14,7 +14,7 @@ line_length = 79
 multi_line_output = 0
 known_standard_library = pkg_resources,setuptools
 known_first_party = mmcls
-known_third_party = PIL,matplotlib,mmcv,mmdet,modelindex,numpy,onnxruntime,packaging,pytest,pytorch_sphinx_theme,requests,rich,sphinx,tensorflow,torch,torchvision,ts
+known_third_party = PIL,cv2,matplotlib,mmcv,mmdet,modelindex,numpy,onnxruntime,packaging,pytest,pytorch_sphinx_theme,requests,rich,sphinx,tensorflow,torch,torchvision,ts
 no_lines_before = STDLIB,LOCALFOLDER
 default_section = THIRDPARTY
 

tests/test_utils/test_setup_env.py

@@ -0,0 +1,68 @@
+# Copyright (c) OpenMMLab. All rights reserved.
+import multiprocessing as mp
+import os
+import platform
+
+import cv2
+from mmcv import Config
+
+from mmcls.utils import setup_multi_processes
+
+
+def test_setup_multi_processes():
+    # temp save system setting
+    sys_start_mehod = mp.get_start_method(allow_none=True)
+    sys_cv_threads = cv2.getNumThreads()
+    # pop and temp save system env vars
+    sys_omp_threads = os.environ.pop('OMP_NUM_THREADS', default=None)
+    sys_mkl_threads = os.environ.pop('MKL_NUM_THREADS', default=None)
+
+    # test config without setting env
+    config = dict(data=dict(workers_per_gpu=2))
+    cfg = Config(config)
+    setup_multi_processes(cfg)
+    assert os.getenv('OMP_NUM_THREADS') == '1'
+    assert os.getenv('MKL_NUM_THREADS') == '1'
+    # when set to 0, the num threads will be 1
+    assert cv2.getNumThreads() == 1
+    if platform.system() != 'Windows':
+        assert mp.get_start_method() == 'fork'
+
+    # test num workers <= 1
+    os.environ.pop('OMP_NUM_THREADS')
+    os.environ.pop('MKL_NUM_THREADS')
+    config = dict(data=dict(workers_per_gpu=0))
+    cfg = Config(config)
+    setup_multi_processes(cfg)
+    assert 'OMP_NUM_THREADS' not in os.environ
+    assert 'MKL_NUM_THREADS' not in os.environ
+
+    # test manually set env var
+    os.environ['OMP_NUM_THREADS'] = '4'
+    config = dict(data=dict(workers_per_gpu=2))
+    cfg = Config(config)
+    setup_multi_processes(cfg)
+    assert os.getenv('OMP_NUM_THREADS') == '4'
+
+    # test manually set opencv threads and mp start method
+    config = dict(
+        data=dict(workers_per_gpu=2),
+        opencv_num_threads=4,
+        mp_start_method='spawn')
+    cfg = Config(config)
+    setup_multi_processes(cfg)
+    assert cv2.getNumThreads() == 4
+    assert mp.get_start_method() == 'spawn'
+
+    # revert setting to avoid affecting other programs
+    if sys_start_mehod:
+        mp.set_start_method(sys_start_mehod, force=True)
+    cv2.setNumThreads(sys_cv_threads)
+    if sys_omp_threads:
+        os.environ['OMP_NUM_THREADS'] = sys_omp_threads
+    else:
+        os.environ.pop('OMP_NUM_THREADS')
+    if sys_mkl_threads:
+        os.environ['MKL_NUM_THREADS'] = sys_mkl_threads
+    else:
+        os.environ.pop('MKL_NUM_THREADS')

tools/test.py

@@ -14,6 +14,7 @@
 from mmcls.apis import multi_gpu_test, single_gpu_test
 from mmcls.datasets import build_dataloader, build_dataset
 from mmcls.models import build_classifier
+from mmcls.utils import setup_multi_processes
 
 # TODO import `wrap_fp16_model` from mmcv and delete them from mmcls
 try:
@@ -119,6 +120,10 @@ def main():
     cfg = mmcv.Config.fromfile(args.config)
     if args.cfg_options is not None:
         cfg.merge_from_dict(args.cfg_options)
+
+    # set multi-process settings
+    setup_multi_processes(cfg)
+
     # set cudnn_benchmark
     if cfg.get('cudnn_benchmark', False):
         torch.backends.cudnn.benchmark = True

tools/train.py

@@ -15,7 +15,7 @@
 from mmcls.apis import init_random_seed, set_random_seed, train_model
 from mmcls.datasets import build_dataset
 from mmcls.models import build_classifier
-from mmcls.utils import collect_env, get_root_logger
+from mmcls.utils import collect_env, get_root_logger, setup_multi_processes
 
 
 def parse_args():
@@ -90,6 +90,10 @@ def main():
     cfg = Config.fromfile(args.config)
     if args.cfg_options is not None:
         cfg.merge_from_dict(args.cfg_options)
+
+    # set multi-process settings
+    setup_multi_processes(cfg)
+
     # set cudnn_benchmark
     if cfg.get('cudnn_benchmark', False):
         torch.backends.cudnn.benchmark = True