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To: Doug Rabson <dfr@render.com>
cc: Michael Hancock <michaelh@cet.co.jp>,
        Doug Rabson <dfr@freefall.freebsd.org>,
        freebsd-lite2@freefall.freebsd.org
Subject: Re: cvs commit: src/sys TODO 
In-reply-to: Your message of "Wed, 02 Oct 1996 13:00:33 +0100."
             <Pine.BSF.3.95.961002123950.10204L-100000@minnow.render.com> 
Date: Wed, 02 Oct 1996 20:42:36 +0800
From: Peter Wemm <peter@spinner.dialix.com>
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Doug Rabson wrote:
> On Wed, 2 Oct 1996, Michael Hancock wrote:
> 
> > On Mon, 30 Sep 1996, Doug Rabson wrote:
> > 
> > > dfr         96/09/30 07:20:31
> > > 
> > >   Branch:      sys       LITE2
> > >   Added:       sys       TODO
> > >   Log:
> > >   This is a list of stuff that I think needs to be done before the lite2
> > >   filesystem code is merged into -current.  Feel free to add/remove/chang
    e
> > >   tasks.
> > 
> > I noticed we're merging in simple_lock().
> 
> I think that it would be a good idea to keep the simple_lock stuff since
> it seems to have the promise of multithreading the FS code in a future SMP
> system.  It is almost certainly broken in the current tree since it is
> pretty tricky to test on a uniprocessor.  There is some DEBUG code in
> kern_lock.c which looks as if it might be useful.

A couple of points:
- Kirk McKusick is reportedly putting some serious time into doing the 
VFS's so that they are fully multithreaded, and he's apparently using the 
lite2 kern_lock framework.  We don't want to rule out the chance of using 
his code should it become available and work.  (I hear he's doing some 
contracting for BSDI, I wonder if the FS work is what he's doing for them? 
 If so, it may not be available to us).
- I'm scratching my head over the SMP code's locking and am trying out 
some experiments.  It's looking reasonably promising that we can use the 
kern_lock code to do internal kernel locking above the trap/exception/irq 
layer, thus breaking the global mutex up.  We can provide the raw boolean 
locking primatives etc as appropriate.  It's not really suitable code to 
use it on the raw edge of the kernel entry points, but it looks like it 
can be used above that.

In any case, it will certainly be interesting when the lite2 code meets 
the smp code. :-)

Cheers,
-Peter