[Beowulf] Good demo applications for small, slow cluster

Lux, Jim (337C) james.p.lux at jpl.nasa.gov
Wed Aug 21 07:10:39 PDT 2013


Sorts in general.. Good idea.

Yes, we'll do a distributed computing bubble sort.

Interesting, though.. There are probably simple algorithms which are
efficient in a single processor environment, but become egregiously
inefficient when distributed.

Jim



On 8/20/13 12:11 PM, "Max R. Dechantsreiter" <max at performancejones.com>
wrote:

>Hi Jim,
>
>How about bucket sort?
>
>Make N as small as need be for cluster capability.
>
>Regards,
>
>Max
>---
>
>
>
>On Tue, 20 Aug 2013 maxd at performancejones.com wrote:
>
>> Date: Tue, 20 Aug 2013 00:23:53 +0000
>> From: "Lux, Jim (337C)" <james.p.lux at jpl.nasa.gov>
>> Subject: [Beowulf] Good demo applications for small, slow cluster
>> To: "beowulf at beowulf.org" <beowulf at beowulf.org>
>> Message-ID:
>> 	<F7B6AE13222F1B43B210AA4991836895236966E9 at ap-embx-sp40.RES.AD.JPL>
>> Content-Type: text/plain; charset="us-ascii"
>>
>> I'm looking for some simple demo applications for a small, very slow
>>cluster that would provide a good introduction to using message passing
>>to implement parallelism.
>>
>> The processors are quite limited in performance (maybe a  few MFLOP),
>>and they can be arranged in a variety of topologies (shared bus, rings,
>>hypercube) with 3 network interfaces on each node.  The processor to
>>processor link probably runs at about 1 Mbit/second, so sending 1 kByte
>>takes 8 milliseconds
>>
>>
>> So I'd like some computational problems that can be given as
>>assignments on this toy cluster, and someone can thrash through getting
>>it to work, and in the course of things, understand about things like
>>bus contention, multihop vs single hop paths, distributing data and
>>collecting results, etc.
>>
>> There's things like N-body gravity simulations, parallelized FFTs, and
>>so forth.  All of these would run faster in parallel than serially on
>>one node, and the performance should be strongly affected by the
>>interconnect topology.  They also have real-world uses (so, while toys,
>>they are representative of what people really do with clusters)
>>
>> Since sending data takes milliseconds, it seems that computational
>>chunks which also take milliseconds is of the right scale.  And, of
>>course, we could always slow down the communication, to look at the
>>effect.
>>
>> There's no I/O on the nodes other than some LEDs, which could blink in
>>different colors to indicate what's going on in that node (e.g.
>>communicating, computing, waiting)
>>
>> Yes, this could all be done in simulation with virtual machines (and
>>probably cheaper), but it's more visceral and tactile if you're
>>physically connecting and disconnecting cables between nodes, and it's
>>learning about error behaviors and such that's what I'm getting at.
>>
>> Kind of like doing biology dissection, physics lab or chem lab for
>>real, as opposed to simulation.  You want the experience of "oops, I
>>connected the cables in the wrong order"
>>
>> Jim Lux
>>
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