Intel® DL Streamer Optimize Media-AI pipeline on Intel® Data Center Flex dGPU by Docker

Introduction

In this blog, we will show how to deploy an end-to-end super-resolution pipeline by leveraging OpenVINO^TM Model Server with Demultiplexing in DAG and Custom Node features.

OpenVINO^TM Model Server (OVMS) is a high-performance system for serving models that uses the same architecture and API as TensorFlow Serving and KServe while applying OpenVINO^TM for inference execution. It is implemented in C++ for scalability and optimized for deployment on intel architectures.

Directed Acyclic Graph (DAG) is an OVMS feature that controls the execution of an entire graph of interconnected models defined within the OVMS configuration. The DAG scheduler makes it possible to create a pipeline of models for execution in the server with a single client request.

During the pipeline execution, it is possible to split a request with multiple batches into a set of branches with a single batch. Internally, OVMS demultiplexer will divide the data, process them in parallel and combine the results.

The custom node in OVMS simplifies linking deep learning models into complete pipeline. Custom node can be used to implement all operations on the data which cannot be handled by the neural network model. It is represented by a C++ dynamic library implementing OVMS API defined in custom_node_interface.h.

Super-Resolution Pipeline Workflow

Figure1 shows the super-resolution pipeline in a flowchart, where we use "demultiply_counter=3" without loss of generality. The whole pipeline starts with input data from the Request node via gRPC calls. Batched input data with 5D shape(3,1,3,270,480) is split into a single batch by the DAG demultiplexer. Each single batch of data is fed into a custom node for image preprocessing. The two outputs of the custom node serve as inputs for model A inference. In the end, all inference results are gathered as output C, which will be sent by the Response node to the client via gRPC calls.

Here is an example configuration for the super-resolution pipeline deployed with OVMS.

{
    "model_config_list": [
        {
            "config": {
                "name": "single-image-super-resolution",
                "base_path": "/models/super_resolution_model_preprocessed/",
                "nireq": 1,
                "plugin_config": {
                    "NUM_STREAMS": "1",
                    "INFERENCE_PRECISION_HINT": "bf16",
                    "AFFINITY": "CORE"
                }
            }
        }
    ],
    "custom_node_library_config_list": [
        {
            "name": "sr_preprocess",
            "base_path": "/models/libcustom_node_super_resolution_nhwc.so"
        }
    ],
    "pipeline_config_list": [
        {
            "name": "super_resolution",
            "inputs": [
                "data"
            ],
            "demultiply_count": -1,
            "nodes": [
                {
                    "name": "sr_preprocess_node",
                    "library_name": "sr_preprocess",
                    "type": "custom",
                    "params": {
                        "image_preprocess_method": "SimpleResize",
                        "debug": "false",
                    },
                    "inputs": [
                        {
                            "image": {
                                "node_name": "request",
                                "data_item": "data"
                            }
                        }
                    ],
                    "outputs": [
                        {
                            "data_item": "out1",
                            "alias": "output1"
                        },
                        {
                            "data_item": "out2",
                            "alias": "output2"
                        }
                    ]
                },
                {
                    "name": "super_resolution_node",
                    "model_name": "single-image-super-resolution",
                    "type": "DL model",
                    "inputs": [
                        {
                            "0": {
                                "node_name": "sr_preprocess_node",
                                "data_item": "output1"
                            }
                        },
                        {
                            "1": {
                                "node_name": "sr_preprocess_node",
                                "data_item": "output2"
                            }
                        }
                    ],
                    "outputs": [
                        {
                            "data_item": "129",
                            "alias": "super_resolution_output"
                        }
                    ]
                }
            ],
            "outputs": [
                {
                    "129": {
                        "node_name": "super_resolution_node",
                        "data_item": "super_resolution_output"
                    }
                }
            ]
        }
    ]
}

“pipeline_config_list” contains super-resolution pipeline information, data enter from the “request” node, flow to “sr_preprocess_node” for image preprocessing, generated two outputs will serve as inputs in “super_resolution_node” for inference, gathered inference results will be returned by “response” node.

• "demultiply_count": acceptable input data batch size when Demultiplexing in DAG feature enabled, “demultiply_count” with value -1 means OVMS can accept dynamic batch input data.

“model_config_list”: contains the basic configuration for super-resolution deep learning model and OpenVINO^TM CPU plugin configuration.

• "nireq": set number of infer requests used in OVMS server for deep learning model
• "NUM_STREAMS": set number of streams used in the CPU plugin
• "INFERENCE_PRECISION_HINT": option to select preferred inference precision in CPU plugin. We can set "INFERENCE_PRECISION_HINT":bf16 on the Xeon platform that supports BF16 precision, such as the 4th Gen Intel® Xeon® Scalable processor (formerly codenamed Sapphire Rapids). Otherwise, we should set "INFERENCE_PRECISION_HINT":f32 as the default value.

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“custom_node_library_config_list”: contains the name and path of the custom node dynamic library

Image Preprocessing with libvips in Custom Node

In this blog, we use a single-image-super-resolution model from Open Model Zoo for the super-resolution pipeline. The model requires two inputs according to the model specification. The first input is the original image (shape [1,3,270,480]). The second input is a 4x resized image with bicubic interpolation (shape [1,3,1080,1920]). Both input images expected color space is BGR. Therefore, image preprocessing for input image is required.

Figure2 shows the custom node designed for image preprocessing in the super-resolution pipeline. The custom node takes the original input image as input data. At first, input data is assigned to output 1 without modification. Besides, the input data is resized 4x with bicubic interpolation and assigned as output 2. The two outputs are passed to the model node for inference. For image processing in the custom node, we utilize libvips – an open-source image processing library that is designed to be fast and efficient with low memory usage. Please see the detailed custom node implementation in super_resolution_nhwc.cpp.

Although libvips is very sufficient for image processing operations with less memory, libvips does not provide functionality for layout (NCHW->NHWC) and color space (RGB->BGR) conversion, which is required by the super-resolution model as inputs. Instead, we can integrate layout and color space conversion into models using OpenVINO^TM Preprocessing API.

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Integrate Preprocessing with OpenVINO^TM Preprocessing API

OpenVINO^TM Preprocessing API allows adding custom preprocessing steps into the execution graph of OpenVINO^TM models.

Here is a sample code to integrate layout (NCHW-> NHWC) and color space (BRG->RGB) conversion into the super-resolution model with OpenVINO^TM Preprocessing API.

from openvino.runtime import Core, Layout, Type, serialize
from openvino.preprocess import ColorFormat, PrePostProcessor

core = Core()
input_tensor_name_1 = "0"

model_path = "./super_resolution/1/single-image-super-resolution-1032.xml"
model = core.read_model(model_path)
ppp = PrePostProcessor(model)
# Input 1
ppp.input(input_tensor_name_1).tensor().set_element_type(Type.u8)
ppp.input(input_tensor_name_1).tensor().set_color_format(ColorFormat.RGB)
ppp.input(input_tensor_name_1).tensor().set_layout(Layout('NHWC'))
...
model = ppp.build()
serialize(model, 
          './super_resolution_model_preprocessed/1/single-image-super-resolution-1032.xml',
          './super_resolution_model_preprocessed/1/single-image-super-resolution-1032.bin')

In the code snippet above, we first load the original model and initialize the PrePostProcessor object with the original model. Then we modify the model's 1^st input element type to “uint8”, change the color format from the default “BGR” to “RGB”, and set the layout from “NCHW” to “NHWC”. In the end, we build a new model and serialize it on the disk. The whole model preprocessing can be done offline, please find details in model_preprocess.py.

Build Model Server Docker Image for Super-Resolution Pipeline

Build OVMS docker image with custom node

git clone https://github.com/sammysun0711/model_server.git -b super_resolution_demo
cd model_server
IMAGE_TAG_SUFFIX=-sr make docker_build

Copy compiled custom nodes library to the “models” directory

cp src/custom_nodes/lib/ubuntu/libcustom_node_super_resolution_nhwc.so  models/

Setup client environment

cd models
pip install -r requirement.txt
sudo apt-get install libvips libjpeg-turbo8-dev

Integrate preprocessing with OpenVINO^TM Preprocessing API

python model_preprocess.py

The resulting model will be saved in the “super_resolution_model_preprocessed/1” directory.

Super-Resolution Pipeline Demo

Start the OpenVINO^TM Model Server with docker binding with 8 cores

docker run --cpuset-cpus 0-7 --rm -v ${PWD}:/models -p 9001:9001 \
openvino/model_server:latest-sr \
--config_path /models/image_super_resolution_config_nhwc.json \
--port 9001

Run client with command line

python ovms_client_nhwc.py --grpc_port 9001  --input_images_dir images \
--model_name super_resolution --height 270 --width 480 \
--batch_size 1 -niter 100

Figure 3 shows the original input image (shape 270x480).

Figure 4 shows the resized image (shape 1080x1920) after image preprocessing in the custom node.

Figure 5 shows the inference result of the super-resolution model (shape1080x1920).  

Conclusion

In this blog, we demonstrate an end-to-end super-resolution pipeline deployment with OpenVINO^TM Model Server. The whole pipeline takes dynamic batched images (RGB, NHWC) as input, demultiplexing into single batch data, preprocess with a custom node, runs an inference with a super-resolution model, send gathered inference results to the client in the end.

This blog provides following examples that utilize OpenVINO^TM Model Server and OpenVINO^TM features: 

• Enable OVMS DAG demultiplexing feature
• Provide custom node for image preprocessing using libvips
• Provide sample code for integrating preprocessing into the model with OpenVINO^TM Preprocessing API.
• Support super-resolution end-to-end pipeline with image preprocessing and model inference with OVMS DAG scheduler

Authors: Mingyu Kim, Vladimir Paramuzov, Nico Galoppo

Intel’s newest GPUs, such as Intel® Data Center GPU Flex Series, and Intel® Arc™ GPU, introduce a range of new hardware features that benefit AI workloads. Starting with the 2022.3 release, OpenVINO™ can take advantage of two newly introduced hardware features: XMX (Xe Matrix Extension) and parallel stream execution. This article explains what those features are and how you can check whether they are enabled in your environment. We also show how to benefit from them with OpenVINO, and the performance impact of doing so.

What is XMX (Xe Matrix Extension)?

XMX is a hardware acceleration for matrix multiplication on the newest Intel™ GPUs. Given the same number of Xe Cores, XMX technology provides 4-8x more multiplication capacity at the same precision [1]. OpenVINO, powered by OneDNN, can take advantage of XMX hardware by accelerating int8 and fp16 inference. It brings performance gains in compute-intensive deep learning primitives such as convolution and matrix multiplication.

Under the hood, XMX is a well-known hardware architecture called a systolic array. Systolic arrays increase computational capacity without increasing memory (or register) access. The magic happens by pipelining multiple computations with a single data access, as opposed to the traditional fetch-compute-store pipeline. It is implemented by connecting multiple computation nodes in series. Data is fed into the front, goes through several steps of multiplication-add, and finally is stored back to memory.

How to check whether you have XMX?

You can check whether your GPU hardware (and software stack) supports XMX with OpenVINO™’s hello_query_device sample. When you run the sample application, it lists all detected inference devices along with its properties. You can check for XMX support by looking at the OPTIMIZATION_CAPABILITIES property and checking for the GPU_HW_MATMUL value.

In the listing below you can see that our system has two GPU devices for inference, and only GPU.1 has XMX support.

$ ./hello_query_device
[ INFO ] GPU.0
[ INFO ]        SUPPORTED_PROPERTIES: 
[ INFO ]                Immutable: OPTIMIZATION_CAPABILITIES : FP32 BIN FP16 INT8      
# XMX is not supported
[ INFO ] GPU.1
[ INFO ]        SUPPORTED_PROPERTIES: 
[ INFO ]                Immutable: OPTIMIZATION_CAPABILITIES : FP32 BIN FP16 INT8 GPU_HW_MATMUL    
# XMX is supported

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As mentioned, XMX provides a way to get significantly more compute capacity on a GPU. The next feature doesn’t provide more capacity, but it allows ways to use that capacity more efficiently.

What is parallel execution of multiple streams?

Another improvement of Intel®’s discrete GPUs is to process multiple compute streams in parallel. Certain deep learning inference workloads are too small to fill all hardware compute resources of a given GPU. In such a case it is beneficial to run multiple compute streams (or inference requests) in parallel, such that the GPU hardware has more work to process at any given point in time. With parallel execution of multiple streams, Intel GPUs can increase hardware efficiency.

How to check for parallel execution support?

As of the OpenVINO 2022.3 release, there is only an indirect way to query how many streams your GPU can process in parallel. In the next release it will be possible to query the range of streams using the ov::range_for_streams property query and the hello_query_device_sample. Meanwhile, one can use the benchmark_app to report the default number of streams (NUM_STREAMS). If the GPU does not support parallel stream execution, NUM_STREAMS will be 2. If the GPU does support it, NUM_STREAMS will be larger than 2. The benchmark_app log below shows that GPU.1 supports 4-stream parallel execution.

$ ./benchmark_app -d GPU.0 -m resnet-50.xml -t 1 --hint none
[ INFO ]   NUM_STREAMS: 2      # Single-stream execution is supported
…
$ ./benchmark_app -d GPU.1 -m resnet-50.xml -t 1 --hint none
[ INFO ]   NUM_STREAMS: 4      # 4-stream execution is supported
…

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However, it depends on application usage

Parallel stream execution can bring significant performance benefit, but only when used appropriately by the application. It will bring good performance gain if the application can run multiple independent inference requests in parallel, whether from single process or multiple processes. On the other hand, if there is no opportunity for parallel execution of multiple inference requests, then there is no gain to be had from multi-stream hardware execution.

Demonstration of performance tuning through benchmark_app

DISCLAIMER: The performance may vary depending on the system and usage.

OpenVINO benchmark_app is a very handy tool to analyze performance in various conditions. Here we’ll show the performance trend for an Intel® discrete GPU with XMX and four parallel hardware execution streams.

The performance was measured on a pre-production version of the Intel® Arc™ A770 Limited Edition GPU with 16 GiB of memory. The host system is a 12th Gen Intel(R) Core(TM) i9-12900K with 64GiB of RAM (4 DDR4-2667 modules) running Ubuntu OS 20.04.5 LTS with Linux kernel 5.15.47.

Performance comparison with high-level performance hints

Even though all supported devices in OpenVINO™ offer low-level performance settings, utilizing them is not recommended outside of very few cases. The preferred way to configure performance in OpenVINO Runtime is using performance hints. This is a future-proof solution fully compatible with the automatic device selection inference mode and designed with portability in mind.

OpenVINO benchmark_app exposes the high-level performance hints with the performance hint option for easy configuration of best latency and throughput. In short, latency mode picks the optimal configuration for low latency with the cost of low throughput, and throughput mode picks the optimal configuration for high throughput with the cost of high latency.

The table below shows throughput for various combinations of execution configuration for resnet-50.

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Throughput mode is achieving much higher FPS compared to latency mode because inference happens with higher batch size and parallel stream execution.  You can also see that, in throughput mode, the throughput with fp16 is 5.4x higher than with fp32 due to the use of XMX.

In the experiments below we manually explore different configurations of the performance parameters for demonstration purposes; It is generally not recommended to tune manually. Once the optimal parameters are known, they can be applied in production.

Performance gain from XMX

Performance gain from XMX can be observed by comparing int8/fp16 against fp32 performance because OpenVINO does not provide an option to turn XMX off. Since fp32 computations are not executed by the XMX hardware pipe, but rather by the less efficient fetch-compute-store pipe, you can see that the performance gap between fp32 and fp16 is much larger than the expected factor of two.

We choose a batch size of 64 to demonstrate the best case performance gain. When the batch size is small, the performance difference is not always as prominent since the workload could become too small for the GPU.

$ ./benchmark_app -d GPU.1 -m resnet-50-fp.xml -t 10 --hint none --nstreams 4 -b 64 --infer_precision f32 | grep Throughput
[ INFO ] Throughput:          1076.22 FPS 
$ ./benchmark_app -d GPU.1 -m resnet-50-fp.xml -t 10 --hint none --nstreams 4 -b 64 --infer_precision f16 | grep Throughput
[ INFO ] Throughput:          5915.62 FPS
$ ./benchmark_app -d GPU.1 -m resnet-50-int8.xml -t 10 --hint none --nstreams 4 -b 64 | grep Throughput
[ INFO ] Throughput:          12270.12 FPS

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As you can see from the execution log, fp16 runs ~5.49x faster than fp32. Int8 throughput is ~2.07x higher than fp16. The difference between fp16 and fp32 is due to fp16 acceleration from XMX while fp32 is not using XMX. The performance gain of int8 over fp16 is 2.07x because both are accelerated with XMX.

Performance gain from parallel stream execution

You can see from the log below that performance goes up as we have more streams up to 4. It is because the GPU can handle 4 streams in parallel.

$./benchmark_app -d GPU.1 -m resnet-50-int8.xml -t 10 --hint none --nstreams 1 -b 64 | grep Throughput
[ INFO ] Throughput:          8593.92 FPS
$./benchmark_app -d GPU.1 -m resnet-50-int8.xml -t 10 --hint none --nstreams 2 -b 64 | grep Throughput
[ INFO ] Throughput:          10610.98 FPS
$./benchmark_app -d GPU.1 -m resnet-50-int8.xml -t 10 --hint none --nstreams 4 -b 64 | grep Throughput
[ INFO ] Throughput:          12246.29 FPS
$./benchmark_app -d GPU.1 -m resnet-50-int8.xml -t 10 --hint none --nstreams 8 -b 64 | grep Throughput
[ INFO ] Throughput:          12150.30 FPS

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Note that if the inference workload is large enough, more streams might not bring much or any performance gain. For example, when increasing the batch size, throughput may saturate earlier than at 4 streams.

How to take advantage the improvements in your application

For XMX, all you need to do is run your int8 or fp16 model with the OpenVINO™ Runtime version 2022.3 or above. If the model is fp32(single precision), it will not be accelerated by XMX. To quantize a model and create an OpenVINO int8 IR, please refer to Quantizing Models Post-training. To create an OpenVINO fp16 IR from a fp32 floating-point model, please refer to Compressing a Model to FP16 page.

For parallel stream execution, you can set throughput hint as described in Optimizing for Throughput. It will automatically set the number of parallel streams with best number.

Conclusion

In this article, we introduced two key features of Intel®’s discrete GPUs: XMX and parallel stream execution. Most int8/fp16 deep learning networks can benefit from the XMX engine with no additional configuration. When properly configured by the application, parallel stream execution can bring significant performance gains too!

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[1] In the Xe-HPG architecture, the XMX delivers 256 INT8 ops per clock (DPAS), while the (non-systolic) Xe Core vector engine delivers 64 INT8 ops per clock – a 4x throughput increase [reference]. In the Xe-HPC architecture, the XMX systolic array depth has been increased to 8 and delivers 4096 FP16 ops per clock, while the (non-systolic) Xe Core vector engine delivers 512 FP16 ops per clock – a 8x throughput increase [reference].

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Notices & Disclaimers

​Performance varies by use, configuration and other factors. Learn more at www.Intel.com/PerformanceIndex​​.

Performance results are based on testing as of dates shown in configurations and may not reflect all publicly available ​updates.  See backup for configuration details.  No product or component can be absolutely secure.​​

​​​​See backup for configuration details.  For more complete information about performance and benchmark results, visit www.intel.com/benchmarks

© Intel Corporation.  Intel, the Intel logo, and other Intel marks are trademarks of Intel Corporation or its subsidiaries.  Other names and brands may be claimed as the property of others​.​​

This AI pipeline implements zero-copy between SYCL and OpenVINO through the Remote Tensor API of the GPU Plugin.

1. Introduction

The development of SYCL simplifies the use of OpenCL, which can fully exploit the computing power of GPU in the pipeline. Meanwhile, SYCL has more flexibility to do customized pre- and post-processing of OpenVINO. To further optimize the pipeline, developers can use GPU Plugin to avoid the memory copy overhead between SYCL and OpenVINO. The GPU plugin provides the ov::RemoteContext and ov::RemoteTensor interfaces for video memory sharing and interoperability with existing native APIs, such as OpenCL, Microsoft DirectX, or VAAPI. For details, please refer to the online documentation of OpenVINO.

Based on the pseudocode of the online documentation, here we provide a simple pipeline sample with Remote Tensor API. Because in the rapid iteration of oneAPI, sometimes customers need quick verification so that this sample can be used for testing. OneAPI also provides a real-world, end-to-end example, which optimizes PointPillars for lidar object detection.

2. Components

SYCL preprocessing is based on the Sepia Filter sample, which demonstrates how to convert a color image to a Sepia tone image, a monochromatic image with a distinctive Brown Gray color. The sample program works by offloading the compute-intensive conversion of each pixel to Sepia tone using SYCL*-compliant code for CPU and GPU.

OpenVINO inferencing is based on the OpenVINO classification sample, the input from SYCL filtered image in the device will be sent into OpenVINO as a remote tensor without a memory copy.

Remote Tensor API: Create RemoteContext from SYCL pre-processing’s native handle. After model compiling, do memory sharing between the application and GPU plugin with from cl::Buffer to remote tensor.

auto cl_queue = get_native<backend::opencl>(sycl_queue);
auto remote_context = ov::intel_gpu::ocl::ClContext(core, cl_queue);
ov::CompiledModel compiled_model = core.compile_model(model, remote_context);
auto cl_buffers = get_native<backend::opencl>(image_buf_out);
auto remote_tensor = remote_context.create_tensor(ov::element::u8, {batch, input_height, input_width, 3}, cl_buffers);
infer_request.set_tensor(input_tensor_name, remote_tensor);

3. Build Sample on Linux

Download the source code from the link. Prepare the model and images.

To run the sample, you need to specify a model and image:

Use pre-trained models from the Open Model Zoo. The models can be downloaded using the Model Downloader. Use images from the media files collection.

 source setupvars.sh
mkdir build
cd build
cmake ..
make 

Run on Intel NUC Core 11 iGPU with OpenVINO 2022.2 and oneAPI 2022.3.

./intel64/hello_nv12_input_classification_oneAPI../model/FP32/alexnet.xml ../image/dog512.bmp GPU 2

Sample Output:

  Loaded image with a width of 512, a height of 512 and 3 channels
[ INFO ] OpenVINO Runtime version ......... 2022.2.0
[ INFO ] Build ........... 2022.2.0-7713-af16ea1d79a-releases/2022/2
[ INFO ] 
[ INFO ] Loading model files: ../model/FP32/alexnet.xml
Running on Intel(R) Iris(R) Xe Graphics [0x9a49]
---Load model - 1126ms
---Create an infer request - 0.515ms
Use remote tensor API and set_tensor
No 1. do inf: 
---sycl buffer  - 0.005ms
---sycl filter total time - 93.342ms
---kernel time: 0.051822 milliseconds
---Set tensor - 0.138ms
---Run infer req - 4.725ms
---get tensor - 0.062ms

Top 3 results:

Image ../image/dog512.bmp

classid probability label
------- ----------- -----
176     0.4579958   "Saluki, gazelle hound"
212     0.2727944   "English setter"
169     0.0513433   "borzoi, Russian wolfhound"

---sum of inference - 98.268ms
No 2. do inf: 
---sycl buffer  - 0.001ms
---sycl filter total time - 0.582ms
---kernel time: 0.05177 milliseconds
---Set tensor - 0.086ms
---Run infer req - 4.162ms
---get tensor - 0.049ms

Top 3 results:

Image ../image/dog512.bmp

classid probability label
------- ----------- -----
176     0.4579958   "Saluki, gazelle hound"
212     0.2727944   "English setter"
169     0.0513433   "borzoi, Russian wolfhound"

---sum of inference - 4.881ms 

Warning: With the updating of OpenVINO and oneAPI, different versions may cause problems with the tools in the common directory or the new SYCL header name. Please use the same version or debug following the corresponding release instructions.