[mvapich-discuss] Same nodes different time?

[Jonathan Perkins]

Hi Daniel.  The order of hosts in your hostfile may impact the mapping
of mpi ranks to which node they run on.  This mixed with your
application's communication pattern may result in different
performance of the application.  I believe this is what you're seeing.

When using mpirun without specifying the hostfile or hosts on the
command line your ranks will all launch on the localhost unless this
is invoked under a slurm or other resource management environment.

On Thu, Mar 27, 2014 at 3:10 PM, Daniel WEI <lakeat at gmail.com> wrote:
> Dear List,
>
> Is it possible that:
>
> hosts (1):
> node1:16
> node2:16
> node3:16
> node4:16
>
> gives a different results than
>
> hosts (2):
> node2:16
> node4:16
> node3:16
> node1:16
>
> I mean does the node sequence appears in the hostfile matter (suppose
> node1~node4 are exactly the same architecture) concerning the speed?
>
> If I use simple mpirun -np XX blahblah, how mvapich2 generated this node
> sequence? Based on what? Which node is going to be the host node, which are
> going to be the slave nodes? Is it a random decision?
>
> My simulation go different wall clock time at the end of 100 time steps of
> my simulations, the residuals and everything is the same, I have checked of
> the log and the results, it is just the time taken for each time step is
> different. Is it a memory issue or oversubscription issue? Has anyone
> experience this situation before?
>
>
> Thanks a lot,
>
>
>
>
> Zhigang Wei
> ----------------------
> University of Notre Dame
>
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-- 
Jonathan Perkins
http://www.cse.ohio-state.edu/~perkinjo