-----Original Message-----
From: kernelnewbies-boun...@kernelnewbies.org
[mailto:kernelnewbies-boun...@kernelnewbies.org] On Behalf Of Vincenzo Scotti
Sent: Friday, March 20, 2015 4:20 PM
To: kernelnewbies@kernelnewbies.org
Subject: Kernel thread scheduling
Hello,
I am actually studying kernel threads, and I have some doubts about them.
Let's take for example this snippet of code
static int thread_function(void *data)
{
while (!kthread_should_stop()) {
schedule();
}
pr_err("Stopped");
return 0;
}
This way it works just fine, and waits until I call kthread_stop on it.
But if I comment out that schedule() call, it just hangs my system when I load
it (it is part of a module). I see that the loop-schedule-wakeup pattern is
used among all the others kernel threads. But I don't get why I need to call
the scheduler explicitly.
I know that the kernel is fully preemptible, and in my interpretation I thought
that it could stop every running thread, even in kernel space, using a
timer-based interrupt handler, to give cpu to other threads. Doesn't this
pattern resemble a voluntary preemption model?
Where am I wrong?
Are you sure your kernel is configured with kernel preemption on? It is a
configurable option. Grep for PREEMPT in your .config file.
Jeff
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