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Subject: Re: [OMPI users] MXM vs OpenIB
From: Shamis, Pavel (shamisp_at_[hidden])
Date: 2013-01-22 16:58:31


>
> Our jobs range from 4 cores to 1000 cores, looking at the FAQ page it states that MXM was used in the past only for >128 ranks, but is in 1.6 used for rank counts of any size.

This is reasonable threshold if you use openib btl with RC (default). Since XRC provides better scalability, you may move the threshold up. Bottom line you have to experiment and see what is good for you :)

-Pasha

>
> Brock Palen
> www.umich.edu/~brockp
> CAEN Advanced Computing
> brockp_at_[hidden]
> (734)936-1985
>
>
>
> On Jan 22, 2013, at 2:58 PM, Shamis, Pavel wrote:
>
>>> We just learned about MXM, and given most our cards are Mellonox ConnectX cards (though not all, have have islands of previous to ConnectX and Qlogic supported in the same OpenMPI environment),
>>>
>>> Will MXM correctly fail though to PSM if on qlogic gear and fail though to OpenIB if on previous to connectX cards?
>>
>> Do you want to run MXM and PSM in the same MPI session ? You can't do it. MXM and PSM use different network protocols.
>> If you want to use MXM in your MPI job, all nodes should be configured to use MXM.
>>
>> On the other hand, OpenIB btl should support mixed environments out of the box.
>>
>> - Pasha
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