How to limit system processes cpu usage? Some system processes like systemsoundservd, logd, diagnosticd, etc. recently use a lots of cpu on my macbook pro. How can I limit them to some degree because most of them are not too relevant to me?

Note: I have already checked out Can I manually limit the %CPU used by a process? but it does not seem to work as expected.

viet@Mozg  ~  pgrep -l systemsoundserv  
506 systemsoundserv  
viet@Mozg  ~  sudo cputhrottle 506 10  
libc++abi.dylib: terminating
with uncaught exception of type Process::ManipulatorException: Error
on task_for_pid of pid 506, res = 5 [1]    7594 abort      sudo
cputhrottle 506 10
Thos system processes respond to other apps that run, so your first step would be to isolate and identify what programs you have that cause high background system load. 

It’s like racing a high performance car and seeing the tires are hot and fuel is being consumed rapidly - those all are the design intent when you press the accelerator to the floor. 

It might make more sense to start with your actual workload than try and hobble or disable logging and sound output. Sorry for a side answer, but those processes sit at idle for the vast majority of installations and likely would on your system if you restart and some troubleshooting should show exactly which of your apps trigger this usage pattern.