Scheduling policy

Hello,

I'm trying to implement a simple scheduling policy in the Linux kernel, but I'm not sure if I correctly understand the sched_class interface. Specifically, I would like to know more about the following functions:

* put_prev_task(struct rq *rq, struct task_struct *prev)
Q: It means the prev was preempted and I have to reschedule another task? Or I have just to add prev to the running queue?

The code should look something like:

if (prev->se.on_rq)
{
enqueue_task(rq, prev);
}

or I'm wrong?

* task_tick(struct rq *rq, struct task_struct *p, int queued)
Q: Should I preempt the task p, by calling resched_task? What does "queued" means?

Thanks,

Lauren?iu Dasc?lu

There's some useful information about sched_class interface inside [1], check 'Scheduler Classes', page 89.

put_prev_task first announces to the scheduler class that the currently running task is going to be replaced by another one.

So I guess, that prev was preempted but it is still in the running queue. Now the scheduler has to dequeue it, and to schedule another task.

Why do you want to enqueue prev? Isn't rq supposed to hold the current running tasks?

thanks,
Daniel.

[1] Professional Linux Kernel Architecture, W. Mauerer