Shutting down cores. CPU hotplug

Core 0 can not be shutted down as some architectures may have some special dependency on a certain CPU.

echo 0 | sudo tee /sys/devices/system/cpu/cpu4/online

Possible states

cat /sys/devices/system/cpu/hotplug/states

Change a target

echo 140 > /sys/devices/system/cpu/cpu4/hotplug/target

CPU governor

List governors

sudo cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_governors

Set governor

echo performance | sudo tee /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor

cat /proc/interrupts

cat /proc/stat
---
cpu  863551 3429 857793 8085941 31541 33767 19313 0 33353 0

Meaning:

user: normal processes executing in user mode
nice: niced processes executing in user mode
system: processes executing in kernel mode
idle: twiddling thumbs
iowait: In a word, iowait stands for waiting for I/O to complete. But there are several problems:
Cpu will not wait for I/O to complete, iowait is the time that a task is waiting for I/O to complete. When cpu goes into idle state for outstanding task io, another task will be scheduled on this CPU.
In a multi-core CPU, the task waiting for I/O to complete is not running on any CPU, so the iowait of each CPU is difficult to calculate.
The value of iowait field in /proc/stat will decrease in certain conditions. So, the iowait is not reliable by reading from /proc/stat.
irq: servicing interrupts
softirq: servicing softirqs
steal: involuntary wait
guest: running a normal guest
guest_nice: running a niced guest
https://www.kernel.org/doc/Documentation/filesystems/proc.txt