kern_threads.c.. upcall question..

[Julian Elischer]

On Tue, 6 May 2003, David Xu wrote:

> 
> ----- 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. :-)

this is what I was thinking..
get_mcontext_user(td, addr)
[...]


> 
> 
> > > + 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.


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..

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