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.
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.
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
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.
For even more detailed logging, flag "-g" can be specified to enable the daemon to log the computations made during the core of the PID loop.
The log output is in CSV format, in the same directory as specified with the "-l" option. Default is the system temporary directory, typically /tmp.
Two files will be created, for each PID loop configured. The pidcoeffs.* file will show the PID coefficients that are in use for the PID loop. The pidcore.* file will show the computations that take place, to transform the input into the output. The configured name of the PID loop is used as the suffix, for both of these files.
The pidcoeffs.* file will grow slowly, updated only when new coefficients are set using D-Bus without restarting the program. The pidcore.* file, on the other hand, will grow rapidly, as it will be updated during each PID loop pass in which there were changes. To prevent needless log file growth, identical logging lines are throttled, unless it has been at least 60 seconds since the last line.
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.
/usr/share/swampd/config.json used for PID control/etc/thermal.d/setpoint, run swampd manually with swampd -l ${LOG_PATH}&, and kill the process after desired duration.fan_rpm_loop_test.sh to configure fan setpoint in steps and collect logs${LOG_PATH}/zone_*.log and analyze response data/usr/share/swampd/config.json as needed