kern_threads.c.. upcall question..

[Julian Elischer]

On Tue, 6 May 2003, David Xu wrote:

> > > 
> > > This is quantum preemptive for userland, it is used when statclock
> > > interrupt hit in userland, if thread quantum is exhausted,
> > > it must unbind upcall from current thread, and schedule an upcall,
> > > you can think it is an implicit syscall triggered by CPU automatically
> > > which just means to swap out current thread.
> > 
> > 
> > ah..
> > I was thinking that we could delay most of thread_user_enter()
> > until we need it..
> > i.e why read the mailbox until we need it..
> > 
> 
> I think fuword is very fast, at least in i386, there is
> few instructions in fuword, please read its code in
> /sys/i386/i386/support.s, optimizing it may be not worth to do.
> Beside this, you can not fetch mailbox pointer on damand, 
> thread_schedule_upcall is protected under sched lock, it 
> can not handle page fault at that time, and kse_thr_interrupt
> need a mailbox pointer to indentify thread in kernel, delaying
> it will cause problem.

Currently we cannot identify threads that are getting pagefaults
or other reasons to enter the kernel except for syscall.

I think there are probably ways that this can be optimised, but it is
not important to do it now.


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