Hi Steve,
See my comments below.
On 12/12/05, Hsieh Steve <stevecfhsieh@xxxxxxxxx> wrote:
> In linux 2.4 the kernel is non-preemptive
> That is, at any time, a process running in kernel mode can not be preempted
> by another user process, right?
I think the confusion is between Kernel is non-preemptive and
kernel running on behalf of a user process ( s/m call ). I think when
a user process calls a system call, then the user job is done by
kernel.
> Consider a user process issue a syscall, trap into kernel and when it stay
> in kernel mode, the timer interrupt comes and
> the process find the its own time quantum is used up(task_struct->counter
> <=0)
> it should be schduled out after timer interrupt complete, right?
Yes. It should be pre-empted. But I think it is not that Kernel is
going to be pre-empted.
AFAIK, Non-Preemptive kernel applies to scheduler and other stuffs
that we have read in theory.
> then , if another user process scheduled to run issue a syscall, what happen?
> is it allowed to trap into kernel?
I saw the schedule() function. And it doesn't distinguish any
process for this state.
It saves the process context and loads a new process.
This is what I understood from the code. I could be wrong. I
welcome comments.
Thanks
-- vijayck
--
Kernelnewbies: Help each other learn about the Linux kernel.
Archive: http://mail.nl.linux.org/kernelnewbies/
FAQ: http://kernelnewbies.org/faq/
