[Beowulf] Heterogeneity in a tiny (two-system cluster)?

[John Hearns]

Oh, and while you are at it.
DO a bit of investigation on how the FVCOM model is optimised for use with
AVX vectorisation.
Hardware and clock speeds alone don't cut it.


On 16 February 2018 at 09:39, John Hearns <hearnsj at googlemail.com> wrote:

> Ted,
> I would go for the more modern system. you say yourself the first system
> is two years old. In one or two years it will be out of warranty, and if a
> component breaks you will have to decide to buy that component or just junk
> they system.
>
>
> Actually, having said that you should look at the FVCOM model and see how
> well it scales on a multi-core system.
> Intel are increasign core counts, but not clock speeds. PAradoxically in
> the past you used to be able to get dual-core parts at over 3Ghz, which
> don;t have many cores competing for bandwith to RAM.
> The counter example to this is Skylake which has more channels to RAM,
> makign for a more balannced system.
>
> I would go for a Skylake system, populate all the DIMM channels, and quite
> honestly forget about runnign between two systems unless the size of your
> models needs this.
> Our latest Skylakes have 192Gbuytes of RAM for that reason. Int he last
> generation this would sound like an unusual amount of RAM, but it makes
> sense in the Skylake generation.
>
>
>
>
>
>
>
>
>
> On 15 February 2018 at 14:20, Tad Slawecki <tslawecki at limno.com> wrote:
>
>>
>> Hello, list -
>>
>> We are at a point where we'd like to explore a tiny cluster of two
>> systems to speed up execution of the FVCOM circulation model. We already
>> have a two-year-old  system with two 14-core CPUs (Xeon E-2680), and I have
>> budget to purchase another system at this point, which we plan to directly
>> connect via Infiniband. Should I buy an exact match, or go with the most my
>> budget can handle (for example 2xXeon Gold 1630, 16-cores) under the
>> assumption that the two-system cluster will operate at about the same speed
>> *and* I can reap the benefits of the added performance when running smaller
>> simulations independently?
>>
>> Our list owner already provided some thoughts:
>>
>> > I've always preferred homgenous clusters, but what you say is,
>> > I think, quite plausible.  The issue you will have though is
>> > ensuring that the application is built for the earliest of the
>> > architectures so you don't end up using instructions for a newer
>> > CPU on the older one (which would result in illegal instruction
>> > crashes).
>> >
>> > But there may be other gotchas that others think of!
>>
>> Thank you ...
>>
>> Tad
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>
>
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