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

[Scott Atchley]

If it is memory bandwidth limited, you may want to consider AMD's EPYC
which has 33% more bandwidth.

On Fri, Feb 16, 2018 at 3:41 AM, John Hearns via Beowulf <
beowulf at beowulf.org> wrote:

> 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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