[mvapich-discuss] Re: loopback with mvapich2-1.2p1

[Dhabaleswar Panda]

> Re factored the question,
> Whether mvapich2-1.2p1 supports loopback connections??

Yes.

> As with Intel MPI we can specify device as "rdma" or "rdssm" where "rdssm"
> does _no_ loopback whereas "rdma" does both loopback as well as non-loopback
> connections with both IMB-MPI1 and IMB-EXT.

The runtime environmental parameter MV2_USE_SHARED_MEM controls this.  By
default, this is set to 1 which uses intra-node shared memory for
communication. If this parameter is set to 0, communication takes place
over loopback connection.

More details on this parameter are available from MVAPICH2 1.2p1 user
guide at the following URL:

http://mvapich.cse.ohio-state.edu/support/user_guide_mvapich2-1.4rc1.html#x1-15600011.70

However, before changing this parameter to 0, you need to make sure that
the underlying network adapter supports loopback connection. Some adapters
do not support such functionality and this option (MV2_USE_SHARED_MEM=0)
may not work with these adapters.

Hope this helps.

DK

>
> On Tue, Aug 4, 2009 at 11:59 AM, gossips J <polk678 at gmail.com> wrote:
>
> > Hi,
> > I would like to know whether mvapcih2-1.2p1 makes loopback connections or
> > not.
> >
> > Does anybody have idea on the same?
> >
> > I could not locate this details on FAQ as well as user guide for the same.
> >
> > Thanks,
> > Polk.
> >
>