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tuning.md

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PID Control Tuning & Logging

The openBMC PID control daemon, swampd (phosphor-pid-control) requires the user to specify the sensors and PID coefficients. Determining good coefficients is beyond the scope of this document.

NOTE The steps below may not be applicable if you are using D-Bus based configuration.

Tuning Fan PID Using a Fixed RPM Setpoint

Flag "-t" can be specified to enabled the daemon to read the fan RPM setpoint from a file /etc/thermal.d/setpoint instead from D-Bus.

The value in the setpoint file is expected to be a normal decimal integer, such as 4000 or 5000, and is in RPM.

Tuning Fan PID Control Parameters

phosphor-pid-control reads PID control values from /usr/share/swampd/config.json, one can modify the PID parameters in the config file and restart the daemon to make the new values effective.

systemctl restart phosphor-pid-control.service

Logging

Flag "-l \<path\>" can be specified to enable the daemon to log fan control data into path. The log output is in CSV format with the following header:

epoch_ms,setpt,fan1,fan2,...fanN,fleeting,failsafe

phosphor-pid-control will create a log for each PID control zone.

Fan RPM Tuning Helper script

https://github.com/openbmc/phosphor-pid-control/blob/master/tools/fan_rpm_loop_test.sh is an example script on how to sweep through available RPM setpoints and log the fan responses.

Thermal Tuning Example

  1. Create initial /usr/share/swampd/config.json used for PID control
  2. (Option 1) If using a fixed setpoint, write the value to /etc/thermal.d/setpoint, run swampd manually with swampd -l ${LOG_PATH}&, and kill the process after desired duration.
  3. (Option 2) If sweeping fan setpoint, using the tuning helper script fan_rpm_loop_test.sh to configure fan setpoint in steps and collect logs
  4. Parse logs from ${LOG_PATH}/zone_*.log and analyze response data
  5. Modify /usr/share/swampd/config.json as needed
  6. Repeat from step 2 or step 3