kernel idle fucntion......

[Murali N]

Hi,
I have one basic doubt on kernel idle function. Who called the kernel
cpu_idle function?
I know a theory that it gets called when there is no activity in the
system? Here i have the following question.

1. How cpu knows that there is nothing to be left out to run?
scheduler get to know this by looking the RUN queue?

Also in 'kernel/arch/arm/process.c' file i saw a variable called
'hlt_counter', what exactly is this variable?

Can somebody share your thoughts on this

-- 
Regards,
Murali N