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Date: Mon, 3 Dec 2001 18:23:35 -0800 (PST)
From: Davide Libenzi <davidel@xmailserver.org>
X-X-Sender: davide@blue1.dev.mcafeelabs.com
To: Donald Becker <becker@scyld.com>
cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: Linux/Pro  -- clusters
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On Mon, 3 Dec 2001, Donald Becker wrote:

> On Mon, 3 Dec 2001, Davide Libenzi wrote:
>
> > On Mon, 3 Dec 2001, Donald Becker wrote:
> > > of the change.  We won't know for years if redesigning the kernel for
> > > large scale SMP system is useful
> > >   - does it actually work,
> > >   - will big SMP machines be common, or even exist?
> > >   - will big SMP machines have the characteristics we predict
> > > let alone worth the costs such as
> > >   - UP performance hit
> > >   - complexity increase slows other improvements
> > >   - difficult performance tuning
> ...
> > No, I do not believe in 128 single CPU SMP machines but, if I've to watch
> > inside my pretty dirty crystal ball, I see multi-core CPUs as a technology
> > response to SMP request.
> > Yes, because after the 1st theorem of "work" there's the 1st lemma of
> > technology that states that "technology will always follow the
> > market request".
>
> You haven't addressed the points above.
> We haven't established that the market will request substantial numbers
> of 128-way SMPs.  Even if they do request single-address-space
> multiprocessors, it's very likely that the result will be some form of cc-numa
> where the structure will strongly influence the OS to treat the machine
> as something besides a SMP.
>
> To bring this branch back on point: we should distinguish between
> design for an arbitrary and unpredictable goal (e.g. 128 way SMP)
> vs. putting some design into things that we are supposed to already
> understand
>    a SCSI device layer that isn't three half-finished clean-ups
>    a VFS layer that doesn't require the kernel to know a priori all of
>      the filesystem types that might be loaded

Donald, I'm not even thinking about planning a 128 CPU scalability for
Linux.
The whole point of this discussion ( if any ) is that we've to design on
what we've or on what we expect to have in a very near future.
We cannot play with technology on long term plans because, no matter how
good we plan, it'll screw us up.




- Davide


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