The STKa8MPxL supports DVFS (dynamic voltage and frequency scaling). By default the governor ondemand is set.
Governors are power schemes for the CPU. Only one can be active at a time.
| Governor | Description |
|---|---|
| performance | Run the CPU at the maximum frequency. |
| powersave | Run the CPU at the minimum frequency. |
| userspace | Run the CPU at user-specified frequencies. |
| ondemand | Scales the frequency dynamically according to current load. Jumps to the highest frequency and then possibly back down as the idle time increases. |
| conservative | Scales the frequency dynamically according to current load. Scales the frequency more gradually than ondemand. |
| schedutil | Scheduler-driven CPU frequency selection |
You can change the current governor with the following command:
cpufreq-set -g <governor> (e.g. cpufreq-set -g performance)
At runtime it is possible to disable multiple CPU cores via the Linux sysfs. On a system that has four CPU cores, a maximum of three cores can be disabled.
To disable a CPU core, the value 0 must be written to the CPU core specific file /sys/devices/system/cpu/cpu<N>/online where <N> is the number of the Core (the counting starts at zero).
e.g. disable the forth CPU core:
echo 0 > /sys/devices/system/cpu/cpu3/online
To check which CPU core(s) are currently enabled the following command can be used:
grep "processor" /proc/cpuinfo
The CPU core can be enabled again by writing the value 1 to /sys/devices/system/cpu/cpu<N>/online.
e.g. enable the forth CPU core:
echo 1 > /sys/devices/system/cpu/cpu3/online
It is possible to limit the maximium amount of cores with the the maxcpus= parameter in the kernel command line. To add the new parameter a new U-boot variable addcpu has to be created.
setenv addcpu maxcpus=${cpu_num}
The amount of cores is set by the cpu_num variable, for example if cpu num is set to 2 only two cores will be started.
setenv cpu_num 2