Open MPI logo

Open MPI User's Mailing List Archives

  |   Home   |   Support   |   FAQ   |  

This web mail archive is frozen.

This page is part of a frozen web archive of this mailing list.

You can still navigate around this archive, but know that no new mails have been added to it since July of 2016.

Click here to be taken to the new web archives of this list; it includes all the mails that are in this frozen archive plus all new mails that have been sent to the list since it was migrated to the new archives.

Subject: [OMPI users] mpi functions are slow when first called and become normal afterwards
From: rightcfd (rightcfd_at_[hidden])
Date: 2009-10-29 15:39:32

We installed a linux cluster recently. The OS is Ubuntu 8.04. The
network is infiniband. We run a simple MPI program to compute the
value of pi. The program follows three stages: MPI_Bcast, computation
and MPI_Reduce. We measure the elapsed time on computation and
communication, respectively. We also repeat the entire process in a
loop terminated by user input. We run the program interactively using
mpirun. We found an weird problem.

When MPI_Bcast and MPI_Reduce are called for the first time, they are
very slow. But after that, they run at normal and stable speed. Is
there anybody out there who have encountered such problem? If you need
any other information, please let me know and I'll provide. Thanks in