detect idle and suspend the CPU

["Nguyen Xuan Hoang" <jerry.nguyen@serialsystem.com.sg>]

Hi,

I am writting a code to automatically suspend the CPU (MPC823) and system
after it goes idle a few minutes.

I try to modify the idled() function in /arch/ppc/kernel/idle.c to count if
the CPU running in this code more than 5 minutes without reschedule , so I
will consider it idle.

for(;;)
{
    if(work) start_idle = jiffies;
    if(jiffies - start_idle > HARD_IDLE_TIMEOUT) {
        detect_idle(); // suspend CPU here
    }
    work = current->need_resched;
    __sti();
    check_pgt_cache();
    ....
}

However just after every 20s, the current->need_resched turn on, as a result
I can not detect the system idle (I already kill all process, excepet
init,kupdate,bdflush,sh).

I found out the init will automatically wake up after 20s.

My question is:

1. How the Linux Kernel for PC do this? I can see PC will automatically
suspend after 15 minutes.

2. Where should be the best place to put the suspend code ? (in idled() ?)

3. Is there anyone have implemented this feature for MPC823, where can I get
the information?

Thank in advances
Jerry


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