[mvapich-discuss] one-sided passive communications

[sreeram potluri]

Maria,

As Jim pointed out, enabling MPI_THREAD_MULTIPLE in this case is taken care
of internally by the MPI library. So you will not need any changes to your
application. It should work with just MPI_Init.

However, make sure to disable affinity using MV2_ENABLE_AFFINITY=0 along
with MPICH_ASYNC_PROGRESS=1. This is required for MVAPICH2 to launch the
async progress thread.

Sreeram Potluri

On Tue, Dec 11, 2012 at 8:09 AM, "María J. Martín" <
maria.martin.santamaria at udc.es> wrote:

> Hi Sreeram,
>
> One more question. Is it necessary to substitute MPI_init by
>  MPI_Init_thread with  required = MPI_THREAD_MULTIPLE  in order to make use
> of the helper threads?
>
> Thanks,
>
> María
>
>
>
> El 05/12/2012, a las 17:10, sreeram potluri escribió:
>
> Hi Maria,
>
> Truly passive one-sided communication is currently supported at the
> intra-node level (with LiMIC and shared memory-based windows), but not at
> the inter-node level. Please refer to the following sections of our user
> guide for further information on the intra-node designs
>
> LiMIC:
> http://mvapich.cse.ohio-state.edu/support/user_guide_mvapich2-1.9a2.html#x1-540006.5
> Shared Memory Based Windows:
> http://mvapich.cse.ohio-state.edu/support/user_guide_mvapich2-1.9a2.html#x1-550006.6
>
> But, you can enable asynchronous progress for inter-node communication by
> using helper threads. This can be done using the runtime parameters:
>
> MPICH_ASYNC_PROGRESS=1 MV2_ENABLE_AFFINITY=0
>
> However, as this involves a helper thread per process, you might see a
> negative impact on performance when running MPI jobs in fully subscribed
> mode, due to contention for cores. Do let us know if you have further
> questions.
>
> As a side note, we suggest that you move to our latest standard release
> MVAPICH2 1.8.1 as it has several features and bug fixes compared to 1.7.
>
> Best
> Sreeram Potluri
>
> On Wed, Dec 5, 2012 at 7:15 AM, "María J. Martín" <
> maria.martin.santamaria at udc.es> wrote:
>
>> Hello,
>>
>> We are using MVAPICH2.1-7 to run an asynchronous algorithm using
>> one-sided passive communications on an Infiniband cluster. We observe that
>> some unlocks take a long time to progress. If extra mpi calls are inserted,
>> the times spent in some unlock calls decrease. It seems that the target of
>> the remote operation should enter the MPI library to progress the unlock
>> calls. However, we had understood from this article
>> http://nowlab.cse.ohio-state.edu/publications/conf-papers/2008/santhana-ipdps08.pdf that
>> this requirement was avoided through the use of RDMA data transfers. We
>> have executed with the MV2_USE_RDMA_ONE_SIDED parameter set to 1 and to 0
>> but none difference was observed in the execution times. Any clarification
>> about the behavior of passive one-sided communications would be welcome.
>>
>> Thanks,
>>
>> María
>>
>> ---------------------------------------------
>> María J. Martín
>> Computer Architecture Group
>> University of A Coruña
>> Spain
>>
>>
>>
>> _______________________________________________
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>>
>>
>
>
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