[mvapich-discuss] Allreduce time when using MPI+OpenMP is too large comparing to when using MPI alone

[Bayatpour, Mamzi]

Hello Sarunya,

We've been looking at the issue you reported internally. However, we are not able to reproduce the performance trends you reported. We observed similar performance for MPI with 1 process per node and MPI+OMP with 1 process per node.

Could you please provide more details about the application that you are testing? Are you using MPI_SINGLE_THREAD or MPI_MULTI_THREAD for your MPI_Init function? Are any OpenMP threads running in the background during the MPI_Allreduce call? A small reproducer could help us a lot.

Thanks,
Mamzi


________________________________
From: Bayatpour, Mamzi
Sent: Friday, March 3, 2017 10:12:24 PM
To: mvapich-discuss at cse.ohio-state.edu
Cc: sarunya at vt.edu
Subject: Re: [mvapich-discuss] Allreduce time when using MPI+OpenMP is too large comparing to when using MPI alone


Hello Sarunya,

Thanks for reporting the issue to us. We are taking a look at it and will get back to you soon.

Thanks,
Mamzi



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