Automatically striping large messages across multiple NICs is certainly a very nice feature; I was not aware that OpenMPI does this transparently. (I wonder if other MPI implementations do this or not). However, I have the following concern: Since the communication over an ethernet NIC is most likely over IP, does it take into account the route cost when striping messages? For example, host A and B in the MPD ring might be connected via two NICs, one direct and one via an intermediate router, or one with a large bandwidth and another with a small bandwidth. Does OpenMPI send a smaller chunk of data over a route with a higher cost?
Because of this concern, I think the channel bonding approach someone else suggested is more preferable; all these details will be taken care of at the hardware level instead of at the IP level.
On Dec 6, 2007 9:42 AM, Jeff Squyres <email@example.com
Wow, that's quite a .sig. :-)
Open MPI will automatically stripe large messages across however many
NICs you have. So you shouldn't need to use multiple threads.
The threading support in the OMPI v1.2 series is broken; it's not
worth using. There's a big warning in configure when you enable it. :-)
On Dec 5, 2007, at 9:57 PM, Tee Wen Kai wrote:
> Hi everyone,
> I have installed openmpi-1.2.3. My system has two ethernet ports.
> Thus, I am trying to make use of both ports to speed up the
> communication process by using openmp to split into two threads.
> However, this implementation always cause error. Then I realized
> that I need to build openmpi using --enable-mpi-threads and use
> MPI_Init_thread to initialize. But, the initialization always return
> MPI_THREAD_SINGLE no matter what value I set. Using ompi_info|grep
> Thread, it shows that thread support has already been activated.
> Thus, I seek your help to teach me what other configurations I need
> to set in order to use multi-threads and what are the parameters to
> include in mpirun in order to use the two ethernet ports.
> Thank you very much.
> Many of us spend our time wishing for things we could have if we
> didn't spend half our time wishing.
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