kern_threads.c.. upcall question..

[David Xu]

----- Original Message ----- 
From: "Julian Elischer" <julian at elischer.org>
To: "David Xu" <davidxu at freebsd.org>
Cc: "Daniel Eischen" <eischen at pcnet1.pcnet.com>; <threads at freebsd.org>
Sent: Tuesday, May 06, 2003 3:10 PM
Subject: Re: kern_threads.c.. upcall question..


> 
> 
> On Tue, 6 May 2003, David Xu wrote:
> 
> > I think the following patch is enough:
> 
> I agree that this seems enough from what I was reading.
> (I like patches that have most lines starting with '-' :-)
> 
> 
> > 
> > Index: kern_thread.c
> > ===================================================================
> > RCS file: /home/ncvs/src/sys/kern/kern_thread.c,v
> > retrieving revision 1.129
> > diff -u -r1.129 kern_thread.c
> > --- kern_thread.c 1 May 2003 12:16:06 -0000 1.129
> > +++ kern_thread.c 6 May 2003 06:32:10 -0000
> > @@ -721,41 +721,6 @@
> [...]
> >  void
> > @@ -962,27 +927,25 @@
> >   uintptr_t mbx;
> >   void *addr;
> >   int error,temp;
> > - ucontext_t uc;
> > + mcontext_t mc;
> >  
> >   p = td->td_proc;
> >   kg = td->td_ksegrp;
> >  
> >   /* Export the user/machine context. */
> > - addr = (void *)(&td->td_mailbox->tm_context);
> > - error = copyin(addr, &uc, sizeof(ucontext_t));
> > - if (error) 
> > -  goto bad;
> > -
> > - thread_getcontext(td, &uc);
> > - error = copyout(&uc, addr, sizeof(ucontext_t));
> > - if (error) 
> > + get_mcontext(td, &mc, 0);
> 
> I think this could be optimised even more.
> (why copy the FP regs if they are not valid) (etc).
> but it is an improvement..
> 

Why need we an intermediate mcontext_t, why not
direct copy the context in trap frame to userland space?
This should be fastest. :-)


> > + addr = (void *)(&td->td_mailbox->tm_context.uc_mcontext);
> > + error = copyout(&mc, addr, sizeof(mcontext_t));
> > + if (error)
> >    goto bad;
> >  
> >   /* Exports clock ticks in kernel mode */
> >   addr = (caddr_t)(&td->td_mailbox->tm_sticks);
> >   temp = fuword(addr) + td->td_usticks;
> > - if (suword(addr, temp))
> > + if (suword(addr, temp)) {
> > +  error = EFAULT;
> >    goto bad;
> > + }
> >  
> >   /* Get address in latest mbox of list pointer */
> >   addr = (void *)(&td->td_mailbox->tm_next);
> > 
> > 
> > And should we disable single threading testing or do
> > double checking in thread_user_enter()? I think per-syscall
> > PROC_LOCK is too expensive for us.
> 
> I am not sure which one you refer too.. Which single_threading
> test?
> 
Single threading testing in thread_user_enter(), someone put 
a PROC_LOCK, quoted here:
        /*              
         * First check that we shouldn't just abort.
         * But check if we are the single thread first!
         */
        PROC_LOCK(p);
        if ((p->p_flag & P_SINGLE_EXIT) && (p->p_singlethread != td)) {
                mtx_lock_spin(&sched_lock);
                thread_stopped(p);
                thread_exit();
                /* NOTREACHED */
        }
        PROC_UNLOCK(p);

> BTW, I am a little unsure about the calling of thread_user_enter()
> from thread_userret().
> 

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.

> 
> 
> > 
> > David Xu
> > 
> > 
> > 
> 
>