[mvapich-discuss] one-sided passive communications

[sreeram potluri]

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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