[Beowulf] mpi slow pairs

[Håkon Bugge]

On 29. aug. 2014, at 22.20, Michael Di Domenico wrote:

> i believe all the pairs do pass through a spine.

IB is destination routed. Without knowing your topology and/or traffic pattern, I expect the pairs connected to the same leaf not to go though the spine. And given that is the case, you are vulnerable to the parking-lot problem

>  i'm not familiar
> with the "parking-lot problem", i'll google it, but suspect a
> bazillion hits will come back

You will. But if there are no erroneous components in your system, the behavior of your system is a function of the system itself and the workload given to it. The parking-lot problem might be an explanation of less than perfect bnehaviour. Not saying it is though.


Håkon

> 
> 
>> Sendt fra min HTC
>> 
>> ----- Reply message -----
>> Fra: "Michael Di Domenico" <mdidomenico4 at gmail.com>
>> Til: "Beowulf Mailing List" <Beowulf at beowulf.org>
>> Emne: [Beowulf] mpi slow pairs
>> Dato: fre., aug. 29, 2014 18:09
>> 
>> 
>> 
>> On Fri, Aug 29, 2014 at 11:38 AM, John Hearns <John.Hearns at viglen.co.uk>
>> wrote:
>>>> Also have you run  ibdiagnet to see if anything is flagged up?
>>> 
>>> i've run a multitude of ib diags on the machines, but nothing is popping
>>> out as wrong.  what's weird is that it's only certain pairing of machines
>>> not any one machine in general.
>>> 
>>> Would that then be a problem in one of the blades or a part of the switch?
>> 
>> not sure yet, i think on the spine modules in the switch is silently
>> failing to send traffic a full speed, but i've not been able to
>> "prove" this yet.
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