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Date:      Mon, 16 Dec 1996 12:28:26 +0900 (JST)
From:      Michael Hancock <michaelh@cet.co.jp>
To:        Chuck Robey <chuckr@Glue.umd.edu>
Cc:        smp@freebsd.org
Subject:   Re: General SMP Design
Message-ID:  <Pine.SV4.3.95.961216120734.24818B-100000@parkplace.cet.co.jp>
In-Reply-To: <Pine.OSF.3.95.961215220312.13518A-100000@gilligan.eng.umd.edu>

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On Sun, 15 Dec 1996, Chuck Robey wrote:

> On Mon, 16 Dec 1996, Michael Hancock wrote:
> 
> > http://www-dsg.stanford.edu/papers/non-blocking-osdi/index.html
> > 
> > We have many examples of type-stable memory management in our code.  i.e.
> > a vnode is always an instance of a vnode, it can be a on a free list.  It
> > doesn't change it's type.  The zone allocator is a good thing.
> 
> I read that, but I don't clearly see why TSM was required.  Not talking
> about the benefits, but why it's required by NBS.  Are you clearer, and
> could you explain it without too much verbage (I don't want to make
> everyone read a thesis here 8-> ).

I'm still reading it myself, but I think it is because you don't want a
data structure to change "underneath" you while other higher priority
processes take over your lock and you retry later on.  Type-stable memory
simplifies implementation. 

SMP is complex, which why I think people should read good background
material.  Good infrastructure design can reduce complexity and improve
performance at the same time.

"UNIX Systems for modern architectures" by Schimmel and "UNIX Internals:
the new frontiers" by Vahalia have the traditional approaches.  When
reading that stuff, you can't help wondering if there's a better way to do
solve priority inversion, deadlocks, and all those other SMP problems.

I don't know if NBS is a real silver bullet, but it's cool that find
someone out there thinking about alternatives to what we know today.

Regards,


Mike Hancock




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