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Ethernet/Fieldbus Performance

The following section describes how to optimize an existing Linux system which runs a CODESYS Runtime system while using Ethernet-based fieldbuses. These fieldbuses include, for example, EtherCAT, PROFINET, or EtherNet/IP.

The description here is given as an example for the EtherCAT Master and can also be used in the same way for PROFINET.

Requirements

  • Hardware

    • Desktop PC

    • Linux PC:

      At least one free Ethernet port per real-time sensitive fieldbus – for example EtherCAT Master / PROFINET – for exclusive use.

      Important

      The used port should not be connected by a switch or USB (not even internally).

  • Software

    • CODESYS IDE

    • IEC application with an EtherCAT Master

    • Linux operating system – for example Debian – with a real-time kernel

      For more information, see the following: Performance Optimization

    • CODESYS Runtime system – for example CODESYS Control​ for Linux SL

Configuration

The goal is essentially to make sure that all threads, which are involved in the operation of the CODESYS Runtime system as EtherCAT Masters, run on a predefined CPU with a defined priority. To do this, settings are possible both in the IEC application as well as on the Linux system.

Important

Do not use CPU 0 for this because it is typically used by the operating system for certain system services (housekeeping).

For optimization on the Linux system, it is recommended to use PLCShell commands. The required settings can also be configured via the runtime configuration or directly on the Linux system. For more information, see the following: Performance Optimization

  1. Establish a connection with CODESYS to the runtime system and open the PLCShell.

  2. Set scaling_governor to performance.

    rt-set scaling_governor all performance

  3. Set the CPU frequency. You need to configure these settings directly on the Linux system. For more information, see the following: Setting the CPU frequency on a Linux system.

    In runtime version SP23 and higher, there will be PLCShell commands for setting the CPU frequency.

    First determine the possible frequencies:

    rt-get cpu_frequency

    Example of an output

    _rtsl_img_ethernet_performance.png

  4. Set the frequency (min and max) to a fixed value:

    rt-set cpu_frequency all 3000000

  5. Disable hyperthreading:

    rt-set hyperthreading off

  6. Disable throttling:

    rt-set throttling off

  7. Enable NAPI threads for the used network adapter (here: ens5):

    rt-set napi ens5 on

  8. Determine the IRQ and NAPI threads of the network adapter:

    irq-list

    Example of an output

    _rtsl_img_ethernet_performance_1.png

  9. Use irq-set-prio and irq-set-affinity to increase the priority for network adapters – for example, on 55 – and bind the network adapters to the same CPU – for example, 0x2 for CPU 1.

    Important

    Set the preferences by name, not by number. Numbers can change when the system starts.

    _rtsl_img_ethernet_performance_2.png

  10. Set the respective NAPI threads to the same priority and CPU:

    _rtsl_img_ethernet_performance_3.png

  11. Set the priority of the EtherCAT_Task to 1. This corresponds to the Linux real-time priority 55.

    For more information, see the following: Mapping of Task Priorities on a Linux System

  12. Use a task group to bind the EtherCAT_Task to the same CPU (here: Core 1, corresponds to affinity 0x2):

    _rtsl_img_ethernet_performance_4.png

Case example: EtherCAT, PROFINET, EtherNet/IP

Scenario: 3 Ethernet-based fieldbuses (example EtherCAT, PROFINET, EtherNet/IP) on a Linux system with at least 4 CPUs

The following settings are recommended (CPU 0 is avoided):

Fieldbus

IEC Task Name

IEC Task Priority

IEC Task Core

IRQ Priority

IRQ Affinity

EtherCAT

EtherCAT_Task

1

1

55

0x2 (CPU 1)

PROFINET

Profinet_IOTask

1

2

55

0x4 (CPU 2)

EtherNet/IP

ENIPScannerIOTask

1

3

55

0x8 (CPU 3)

Setting the CPU frequency on a Linux system

Important

The following settings are lost when a Linux system starts and therefore must be reset after a restart.

  1. You can use the following Linux console commands to determine the minimum and maximum CPU frequencies (here: CPU0-3):

    cat /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_max_freq
cat /sys/devices/system/cpu/cpu1/cpufreq/cpuinfo_max_freq
cat /sys/devices/system/cpu/cpu2/cpufreq/cpuinfo_max_freq
cat /sys/devices/system/cpu/cpu3/cpufreq/cpuinfo_max_freq
cat /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_min_freq
cat /sys/devices/system/cpu/cpu1/cpufreq/cpuinfo_min_freq
cat /sys/devices/system/cpu/cpu2/cpufreq/cpuinfo_min_freq
cat /sys/devices/system/cpu/cpu3/cpufreq/cpuinfo_min_freq

    Example of an output

    3800000
3800000
3800000
3800000
1600000
1600000
1600000
1600000

  2. You can use the following commands to set the CPU frequencies:

    echo "3000000" | sudo tee /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq
echo "3000000" | sudo tee /sys/devices/system/cpu/cpu1/cpufreq/scaling_max_freq
echo "3000000" | sudo tee /sys/devices/system/cpu/cpu2/cpufreq/scaling_max_freq
echo "3000000" | sudo tee /sys/devices/system/cpu/cpu3/cpufreq/scaling_max_freq
echo "3000000" | sudo tee /sys/devices/system/cpu/cpu0/cpufreq/scaling_min_freq
echo "3000000" | sudo tee /sys/devices/system/cpu/cpu1/cpufreq/scaling_min_freq
echo "3000000" | sudo tee /sys/devices/system/cpu/cpu2/cpufreq/scaling_min_freq
echo "3000000" | sudo tee /sys/devices/system/cpu/cpu3/cpufreq/scaling_min_freq
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