[mvapich-discuss] one-sided passive communications

["María J. Martín"]

Hi Sreeram,

Thank you for your prompt reply. We will try with the helper threads.

If helper threads are not used, what is needed to get progress in the lock/unlock calls? Is it necessary to enter in any specific MPI call in the target process?

As regards the intra-node optimizations, could they be used for the communications intra-nodes in an MPI execution using more than 1 node?

Thanks again,

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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