Re: Scaling noise

[ebiederm@xmission.com (Eric W. Biederman)]

Larry McVoy <lm@bitmover.com> writes:

> On Sun, Sep 07, 2003 at 09:47:58PM -0700, Stephen Satchell wrote:
> > At 05:57 PM 9/7/2003 -0700, Larry McVoy wrote:
> > >That's not "a machine" that's ~1150 machines on a network.  This business
> > >of describing a bunch of boxes on a network as "a machine" is nonsense.
> > 
> > Then you haven't been keeping up with Open-source projects, or the 
> > literature.  
> 
> Err, I'm in that literature, dig a little, you'll find me.  I'm quite
> familiar with clustering technology.  While it is great that people are
> wiring up lots of machines and running MPI or whatever on them, they've
> been doing that for decades.  It's only a recent thing that they started
> calling that "a machine".  That's marketing, and it's fine marketing,
> but a bunch of machines, a network, and a library does not a machine make.

Oh so you need cache coherency to make it a machine.  That being the only
difference between that and a NUMA box.

Although I will state that there is a lot more that goes into such
a system than a network, and a library.  At least there is a lot more
that goes into the manageable version of one.

> Not to me it doesn't.  I want to be able to exec a proces and have it land
> anywhere on the "machine", any CPU, I want controlling tty semantics,
> if I have 2300 processes in one process group then when I hit ^Z they
> had all better stop.  Etc.

Oh wait none of that comes with cache coherency.  So the difference
cannot be cache coherency.

> A collection of machines that work together is called a network of 
> machines, it's not one machine, it's a bunch of them.  There's nothing
> wrong with getting a lot of use out of a pile of networked machines,
> it's a great thing.  But it's no more a machine than the internet is
> a machine.

Cool so the SGI Ultrix is not a machine.  Nor is the SMP box over in
my lab.  They are separate machines wired together with a network, and
so I better start calling them a network of machines.

As far as I can tell which pile of hardware to call a machine
is a difference that makes no difference.  Marketing as you put it.

The only practical difference would seem to be what kind of problems
you think are worth solving for a collection of hardware.  By calling
it a single machine I am saying I think it is worth solving the single
system image problem.  By refusing to call it a machine you seem to
think it is a class of hardware which is not worth paying attention to.

I do think it is a class of hardware that is worth solving the hard
problems for.  And I will continue to call that pile of hardware a
machine until I give up on that. 

I admit the hard problems have not yet been solved but the solutions
are coming.

Eric