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Subject: Re: [OMPI users] MPI_Spawn and process allocation policy
From: Ralph Castain (rhc_at_[hidden])
Date: 2011-08-16 06:30:59

What version are you using?

On Aug 16, 2011, at 3:19 AM, Simone Pellegrini wrote:

> Dear all,
> I am developing a system to manage MPI tasks on top of MPI. The architecture is rather simple, I have a set of scheduler processes which takes care to manage the resources of a node. The idea is to have 1 (or more) of those scheduler allocated on each node of a cluster and then create new MPI processes (on demand) as computation is needed. Allocation of processes is done using MPI_Spawn.
> The system now works fine on a single node by allocating the main scheduler using the following mpi command:
> mpirun --np 1 ./scheduler ...
> Now when I scale to multiple nodes problems with default MPI behaviour starts. For example lets assume I have 2 nodes with 8 cpu cores each. I therefore set up a machine file in the following way:
> s01 slots=1
> s02 slots=1
> and start the node schedulers in the following way:
> mpirun --np 2 --machinefile machinefile ./scheduler ...
> This allocates the processes correctly, now the problem starts when I invoke MPI_Spawn. basically MPI spawn also uses the informations from the machinefile and if 4 MPI processes are spawned 2 are allocated in s01 and 2 on s02. What I want is to allocate the processes always in the same node.
> I tried to do this by specifying an MPI_Info object which is then passed to the MPI_Spawn routine. I tried to set the "host" property to the hostname of the machine where the scheduler is running but this didn't help.
> Unfortunately there is very little documentation on this.
> Thanks for the help,
> Simone
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