Q: Scheduler and need_resched

Q: Scheduler and need_resched

[Anders Fugmann]

Hi.

I got a small question of what happens codevice when the quantum of a 
task is expired (counter == 0 -> need_resched == 1). Of cource schedule 
is invoked somehow, but from where? How is the "flow". I see from where 
do_timer is called, and that it schedules a BH, but then I'm stuck.

I have a feeling that some function is called (at least) each timer 
tick, which tests if schedules sould be called (a test on need_resched 
amongst others). I just cannot seem to find this function.

Any pointer appriciated.
Anders Fugmann

Re: Q: Scheduler and need_resched

[Anders Fugmann]

Anders Fugmann wrote:
> Hi.
> 
> I got a small question of what happens codevice when the quantum of a 
> task is expired (counter == 0 -> need_resched == 1). Of cource schedule 
> is invoked somehow, but from where? How is the "flow". I see from where 
> do_timer is called, and that it schedules a BH, but then I'm stuck.
> 
> Any pointer appriciated.
> Anders Fugmann

Solved.
By the help of the kernel newbies pages, I was pointed to the page 
http://kernelnewbies.org/wiki/moin.cgi/Karthick, which pointed at
the label '_ret_with_reschedule' in entry.S.

This piece of assembler is called after each interrupt, and tests the 
need_resched flag to see is scheduling is nessesary.

Anyway, thanks for your time.
Anders Fugmann