Asynchronous Inference with OpenVINO™¶
This tutorial is also available as a Jupyter notebook that can be cloned directly from GitHub. See the installation guide for instructions to run this tutorial locally on Windows, Linux or macOS. To run without installing anything, click the launch binder button.
This notebook demonstrates how to use the Async API for asynchronous execution with OpenVINO.
OpenVINO Runtime supports inference in either synchronous or asynchronous mode. The key advantage of the Async API is that when a device is busy with inference, the application can perform other tasks in parallel (e.g. populating inputs or scheduling other requests) rather than wait for the current inference to complete first.
Imports¶
import sys
import cv2
import time
import numpy as np
from openvino.runtime import Core
import openvino.runtime as ov
from IPython import display
import matplotlib.pyplot as plt
sys.path.append("../utils")
import notebook_utils as utils
Prepare model and data processing¶
Download test model¶
We use a pre-trianed model from OpenVINO’s Open Model Zoo to start our test. In this case, the model will be excuted to detect the person in each frame of the video.
# directory where model will be downloaded
base_model_dir = "model"
# model name as named in Open Model Zoo
model_name = "person-detection-0202"
precision = "FP16"
model_path = (
f"model/intel/{model_name}/{precision}/{model_name}.xml"
)
download_command = f"omz_downloader " \
f"--name {model_name} " \
f"--precision {precision} " \
f"--output_dir {base_model_dir} " \
f"--cache_dir {base_model_dir}"
! $download_command
################|| Downloading person-detection-0202 ||################
========== Downloading model/intel/person-detection-0202/FP16/person-detection-0202.xml
========== Downloading model/intel/person-detection-0202/FP16/person-detection-0202.bin
Load the model¶
# initialize OpenVINO runtime
ie = Core()
# read the network and corresponding weights from file
model = ie.read_model(model=model_path)
# compile the model for the CPU (you can choose manually CPU, GPU, MYRIAD etc.)
# or let the engine choose the best available device (AUTO)
compiled_model = ie.compile_model(model=model, device_name="CPU")
# get input node
input_layer_ir = model.input(0)
N, C, H, W = input_layer_ir.shape
shape = (H, W)
Create functions for data processing¶
def preprocess(image):
"""
Define the preprocess function for input data
:param: image: the orignal input frame
:returns:
resized_image: the image processed
"""
resized_image = cv2.resize(image, shape)
resized_image = cv2.cvtColor(np.array(resized_image), cv2.COLOR_BGR2RGB)
resized_image = resized_image.transpose((2, 0, 1))
resized_image = np.expand_dims(resized_image, axis=0).astype(np.float32)
return resized_image
def postprocess(result, image, fps):
"""
Define the postprocess function for output data
:param: result: the inference results
image: the orignal input frame
fps: average throughput calculated for each frame
:returns:
image: the image with bounding box and fps message
"""
detections = result.reshape(-1, 7)
for i, detection in enumerate(detections):
_, image_id, confidence, xmin, ymin, xmax, ymax = detection
if confidence > 0.5:
xmin = int(max((xmin * image.shape[1]), 10))
ymin = int(max((ymin * image.shape[0]), 10))
xmax = int(min((xmax * image.shape[1]), image.shape[1] - 10))
ymax = int(min((ymax * image.shape[0]), image.shape[0] - 10))
cv2.rectangle(image, (xmin, ymin), (xmax, ymax), (0, 255, 0), 2)
cv2.putText(image, str(round(fps, 2)) + " fps", (5, 20), cv2.FONT_HERSHEY_SIMPLEX, 0.7, (0, 255, 0), 3)
return image
Get the test video¶
video_path = "../202-vision-superresolution/data/CEO Pat Gelsinger on Leading Intel.mp4"
How to improve the throughput of video processing¶
Below we compare the performance of the synchronous and async-based approaches:
Sync Mode (default)¶
Let’s see how video processing works with the default approach. Using the synchronous approach, the frame is captured with OpenCV and then immediately processed:
while(true) { * // capture frame // populate CURRENT InferRequest // Infer CURRENT InferRequest //this call is synchronous // display CURRENT result* }
def sync_api(source, flip, fps, use_popup, skip_first_frames):
"""
Define the main function for video processing in sync mode
:param: source: the video path or the ID of your webcam
:returns:
sync_fps: the inference throughput in sync mode
"""
frame_number = 0
infer_request = compiled_model.create_infer_request()
player = None
try:
# Create a video player
player = utils.VideoPlayer(source, flip=flip, fps=fps, skip_first_frames=skip_first_frames)
# Start capturing
start_time = time.time()
player.start()
if use_popup:
title = "Press ESC to Exit"
cv2.namedWindow(title, cv2.WINDOW_GUI_NORMAL | cv2.WINDOW_AUTOSIZE)
while True:
frame = player.next()
if frame is None:
print("Source ended")
break
resized_frame = preprocess(frame)
infer_request.set_tensor(input_layer_ir, ov.Tensor(resized_frame))
# Start the inference request in synchronous mode
infer_request.infer()
res = infer_request.get_output_tensor(0).data
stop_time = time.time()
total_time = stop_time - start_time
frame_number = frame_number + 1
sync_fps = frame_number / total_time
frame = postprocess(res, frame, sync_fps)
# Display the results
if use_popup:
cv2.imshow(title, frame)
key = cv2.waitKey(1)
# escape = 27
if key == 27:
break
else:
# Encode numpy array to jpg
_, encoded_img = cv2.imencode(".jpg", frame, params=[cv2.IMWRITE_JPEG_QUALITY, 90])
# Create IPython image
i = display.Image(data=encoded_img)
# Display the image in this notebook
display.clear_output(wait=True)
display.display(i)
# ctrl-c
except KeyboardInterrupt:
print("Interrupted")
# Any different error
except RuntimeError as e:
print(e)
finally:
if use_popup:
cv2.destroyAllWindows()
if player is not None:
# stop capturing
player.stop()
return sync_fps
Test performance in Sync Mode¶
sync_fps = sync_api(source=video_path, flip=False, fps=30, use_popup=False, skip_first_frames=800)
print(f"average throuput in sync mode: {sync_fps:.2f} fps")
Source ended
average throuput in sync mode: 42.37 fps
Async Mode¶
Let’s see how the OpenVINO Async API can improve the overall frame rate of an application. The key advantage of the Async approach is as follows: while a device is busy with the inference, the application can do other things in parallel (e.g. populating inputs or scheduling other requests) rather than wait for the current inference to complete first.
In the example below, inference is applied to the results of the video decoding. So it is possible to keep multiple infer requests, and while the current request is processed, the input frame for the next is being captured. This essentially hides the latency of capturing, so that the overall frame rate is rather determined only by the slowest part of the pipeline (decoding vs inference) and not by the sum of the stages.
while(true) { * // capture frame // populate NEXT InferRequest // start NEXT InferRequest //this call is async and returns immediately // wait for the CURRENT InferRequest // display CURRENT result // swap CURRENT and NEXT InferRequests* }
def async_api(source, flip, fps, use_popup, skip_first_frames):
"""
Define the main function for video processing in async mode
:param: source: the video path or the ID of your webcam
:returns:
async_fps: the inference throughput in async mode
"""
frame_number = 0
# Create 2 infer requests
curr_request = compiled_model.create_infer_request()
next_request = compiled_model.create_infer_request()
player = None
try:
# Create a video player
player = utils.VideoPlayer(source, flip=flip, fps=fps, skip_first_frames=skip_first_frames)
# Start capturing
start_time = time.time()
player.start()
if use_popup:
title = "Press ESC to Exit"
cv2.namedWindow(title, cv2.WINDOW_GUI_NORMAL | cv2.WINDOW_AUTOSIZE)
# Capture CURRENT frame
frame = player.next()
resized_frame = preprocess(frame)
curr_request.set_tensor(input_layer_ir, ov.Tensor(resized_frame))
# Start the CURRENT inference request
curr_request.start_async()
while True:
# Capture NEXT frame
next_frame = player.next()
if next_frame is None:
print("Source ended")
break
resized_frame = preprocess(next_frame)
next_request.set_tensor(input_layer_ir, ov.Tensor(resized_frame))
# Start the NEXT inference request
next_request.start_async()
# Waiting for CURRENT inference result
if curr_request.wait_for(-1) == 1:
res = curr_request.get_output_tensor(0).data
stop_time = time.time()
total_time = stop_time - start_time
frame_number = frame_number + 1
async_fps = frame_number / total_time
frame = postprocess(res, frame, async_fps)
# Display the results
if use_popup:
cv2.imshow(title, frame)
key = cv2.waitKey(1)
# escape = 27
if key == 27:
break
else:
# Encode numpy array to jpg
_, encoded_img = cv2.imencode(".jpg", frame, params=[cv2.IMWRITE_JPEG_QUALITY, 90])
# Create IPython image
i = display.Image(data=encoded_img)
# Display the image in this notebook
display.clear_output(wait=True)
display.display(i)
# Swap CURRENT and NEXT frames
frame = next_frame
# Swap CURRENT and NEXT infer requests
curr_request, next_request = next_request, curr_request
# ctrl-c
except KeyboardInterrupt:
print("Interrupted")
# Any different error
except RuntimeError as e:
print(e)
finally:
if use_popup:
cv2.destroyAllWindows()
if player is not None:
# stop capturing
player.stop()
return async_fps
Test the perfromance in Async Mode¶
async_fps = async_api(source=video_path, flip=False, fps=30, use_popup=False, skip_first_frames=800)
print(f"average throuput in async mode: {async_fps:.2f} fps")
Source ended
average throuput in async mode: 92.96 fps
Compare the performance¶
width = 0.4
fontsize = 14
plt.rc('font', size=fontsize)
fig, ax = plt.subplots(1, 1, figsize=(10, 8))
rects1 = ax.bar([0], sync_fps, width, color='#557f2d')
rects2 = ax.bar([width], async_fps, width)
ax.set_ylabel("frames per second")
ax.set_xticks([0, width])
ax.set_xticklabels(["Sync mode", "Async mode"])
ax.set_xlabel("Higher is better")
fig.suptitle('Sync mode VS Async mode')
fig.tight_layout()
plt.show()
