[Beowulf] Begginers question # 1

Joshua mora acosta joshua_mora at usa.net
Tue Oct 5 00:27:17 EDT 2010


Hello Gabriel

Beginner's questions are usually the harder ones ;)

Without any personal interest, here you have an easy reading that should help
you break the ice
 
http://www.sun.com/x64/ebooks/hpc_for_dummies.pdf

In my opinion this (ie. HPC) is a very experimental field on both HW and SW so
your best way to learn is by getting on something very affordable, and trying
to use it as much as you can. For that it will be good to get familiarized
with profilers ( performance counter tools ) so you gain confidence in what
you do.
That will force you to learn what is capable the whole thing (specially your
application).
Then once the app can use it all and you find what part of the HW or/and SW is
limiting the performance, start being demanding in that direction (there are
many directions), but one thing at a time or very few at a time if you know
how each thing contributes.

That process is lengthy and the newsgroup could answer much better specific
questions rather than generic ones while you go through it.

At the end, well there is no end, just a continuous refactoring process of
"your own solution" that you impose to yourself while you try to keep up with
the technologies that will allow you to get to the next computational/science
challenge.

Best regards,
Joshua Mora.

------ Original Message ------
Received: 08:53 PM CDT, 10/04/2010
From: Mark Hahn <hahn at mcmaster.ca>
To: gabriel lorenzo <macglobalus at yahoo.com>Cc: beowulf at beowulf.org
Subject: Re: [Beowulf] Begginers question # 1

> > IN CLUSTER COMPUTING, IS THE AMOUNT OF CORE THAT COUNTS?
> 
> no.  it's the application that counts.
> 
> > If I build a cluster with 8 motherboards with 1 single core each would it
> > be the same as using just one motherboard but with two quad core
> > processors?
> 
> of course not.  communication among cores on a single board
> will certainly be faster than inter-board communication. 
> it's the application that matters: how frequently do threads/ranks 
> of the application communicate?  are messages small or large? 
> can the app's communication be formulated as mostly-read sharing of data? 
> these are all very much properties of the application, 
> and they determine how suitable any particular hardware will be.
> 
> > I wanna build one of these but wanna save money and space and
> > if what counts is the amount of cores to process info I think fewer
> > motherboards with dual six-core processors is definitely cheaper just
> > because I wont be needing that many mothers power supplies etc. thanks
> 
> power supplies aren't your main concern, since good ones are about 93%
> efficient.  but going with more-core systems is, in general, a good idea.
> mainly for amortization reasons: probably fewer disks, extraneous sutff
> like video interfaces, fewer parts to fail, fewer systems to administer,
etc.
> there can be disadvantages to more-core systems too, since some of the
parts
> being shared (amortized) may be performance bottlenecks.
> 
> the sweet spots depends on what systems are in volume production - 
> right now, 2-socket systems are the right building block in most cases.
> 4-socket systems would be attractive, but they tend to ship in so much 
> lower volume that their price is nonlinearly high.  1-socket servers 
> tend to cost more than half a 2-socket (where "server" means at least 
> "has ECC memory" - that is, not a desktop.)
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