Intel® VTune™ Profiler Performance Analysis Cookbook

Cookbook

  • 2021
  • 11/09/2021
  • Public Content
Contents

DPDK Event Device Profiling

Use
Intel® VTune™
Profiler
 to analyze the efficiency of DPDK Event Device pipeline utilization in your DPDK-based application and identify issues, such as inhomogeneous load distribution and worker core underutilization.
Content Experts:
 Eugeny Parshutin, Kurakin Ilia
The Data Plane Development Kit (DPDK) is a framework that consists of libraries that accelerate packet processing workloads running on a wide variety of CPU architectures. One of these libraries is the
eventdev
 library that enables you to improve system load balancing by using an event-based model in your application. An event-based approach suggests that the work that needs to be done by the system is presented as separate units called events. One common example of using the event-based programming model in DPDK is the network packet processing pipeline, where each packet plays the role of an event.
This figure gives an example of an
eventdev
 pipeline configuration:
Here, each block represents the following unit:
  • Event Device
     – device with event scheduling capability, implemented either in hardware or software.
  • Queue
     – logical stage of the processing pipeline that contains events of different flows associated with scheduling types (atomic, ordered, or parallel).
  • Ports
     – points of contact between cores and the
    eventdev
     library that are used to enqueue and dequeue events to and from
    eventdev
     queues.
  • Worker Cores
     – CPU cores that are available to the application to perform work.
  • Rx Core
     – CPU core that receives packets from the NIC.
  • Tx Core
     – CPU core that transmits packets to the NIC.
  • NIC
     – Network Interface Card.
This example demonstrates an Event Device that is configured to manage four atomic stages that are presented as four event queues:
  • queue_0
     is dedicated to keep newly arrived packets. Only the Rx core enqueues packets (events) to this queue.
  • queue_1
     and
    queue_2
     are dedicated to some type of event processing stage, such as setting destination address, cryptography processing, or compression. Worker cores perform these tasks and transfer packets between queues 0, 1, 2, and 3.
  • queue_3
     is dedicated to keep packets that are ready to be transmitted. Only the Tx core dequeues packets from this queue.
The dequeue operation is performed using the
rte_event_dequeue_burst()
 routine in an endless loop. Thus, worker cores continuously poll Event Device ports, looking for a batch of events to be processed. The batch size depends on overall load and performance of different stages. The maximum batch size is defined by the workload.
Per-worker dequeue statistics provided by
Intel® VTune™
Profiler
 reveal the load balancing details and enable you to analyze pipeline configuration efficiency and identify pipeline bottlenecks.
This recipe defines the following steps to analyze the efficiency of the pipeline processing model in DPDK-based applications:

Ingredients

This section lists the hardware and software tools used in this performance analysis scenario:
  • Application:
     the DPDK
    eventdev_pipeline
     application demonstrates the usage of the
    eventdev
     API and shows how an application can configure a pipeline and assign a set of worker cores to perform event processing. The application is compiled with DPDK with
    VTune
    Profiler
     support enabled.
  • Tools:
    • DPDK, compiled with
      VTune
      Profiler
       support enabled. To enable
      eventdev
       profiling on DPDK side, you need to apply a patch and recompile DPDK and the target DPDK application.
      Use the following patches:
    • Intel® VTune™
      Profiler
       2020: Input and Output analysis.
      • Starting with the 2020 release, Intel® VTune™ Amplifier has been renamed to
        Intel® VTune™
        Profiler
        .
      • Most recipes in the
        Intel® VTune™
        Profiler
         Performance Analysis Cookbook are flexible. You can apply them to different versions of
        Intel® VTune™
        Profiler
        . In some cases, minor adjustments may be required.
      • Get the latest version of
        Intel® VTune™
        Profiler
        :
  • System Setup:
    • Traffic generator:
       a system that generates traffic for the system being tested.
    • System under test:
       a system running the
      eventdev_pipeline
       application for packet (event) processing and
      VTune
      Profiler
       for performance data collection.
  • CPU:
     Intel® Xeon® Platinum 8168 processor (formerly code named Skylake).
  • Operating System:
     Linux* OS.

Run Input and Output Analysis

To collect DPDK
eventdev
 dequeue statistics, use the Input and Output analysis of
VTune
Profiler
.
To run the analysis from the GUI:
  1. Launch the
    VTune
    Profiler
     GUI and create a new project
  2. In the
    HOW
     pane, select the
    Input and Output
     analysis
  3. In
    Select IO API type to profile
    , select
    DPDK IO API
  4. Click the
    Start
     button.
To run Input and Output analysis with DPDK profiling from the command line, use the following command: 
vtune -collect io -knob kernel-stack=false -knob dpdk=true --target-process=eventdev_pipeline

Analyze Load per Stage

To get an overall characterization of DPDK
eventdev
 pipeline utilization, start your investigation with the
Summary
 tab and explore the
DPDK Events Dequeue Statistics
 histogram:
This histogram represents the statistics for the number of dequeued events for each
eventdev
 port, that is, for each worker thread that polls the event device. Explore the different areas of the histogram to identify inhomogeneous load distribution, oversubscribed, or underutilized workers.
If you identify any imbalance in worker thread load distribution, try to reconfigure your pipeline to avoid this an re-run the analysis.

Analyze CPU Utilization

To understand the CPU utilization for workers performing event dequeue operations, navigate to the
Platform
 tab and explore the
DPDK Event Dequeue Spin Time
 overtime metric attributed to worker threads.
The
DPDK Event Dequeue Spin Time
 per-thread metric shows the ratio of empty dequeue cycles, which is the ratio of
rte_event_dequeue_burst()
 calls that returned zero events with respect to the total number of dequeue calls. Explore this metric to estimate worker thread load and to decide whether the application underutilizes cores or needs more resources.

Product and Performance Information

1

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