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Subject: Re: [OMPI users] MPI_Comm_spawn, caller uses CPU while waiting for spawned processes
From: Ralph Castain (rhc_at_[hidden])
Date: 2009-12-04 10:21:55


You used it correctly. Remember, all that cpu number is telling you is the percentage of use by that process. So bottom line is: we are releasing it as much as we possibly can, but no other process wants to use the cpu, so we go ahead and use it.

If any other process wanted it, then the percentage would drop and the other proc would take some.

On Dec 4, 2009, at 8:13 AM, Nicolas Bock wrote:

> On Fri, Dec 4, 2009 at 08:03, Ralph Castain <rhc_at_[hidden]> wrote:
>
>
> It is polling at the barrier. This is done aggressively by default for performance. You can tell it to be less aggressive if you want via the yield_when_idle mca param.
>
>
> How do I use this parameter correctly? I tried
>
> /usr/local/openmpi-1.3.4-gcc-4.4.2/bin/mpirun -np 3 --mca mpi_yield_when_idle 1 ./master
>
> but still get
>
> nbock 20794 0.0 0.0 53980 2344 pts/2 S+ 08:11 0:00 /usr/local/openmpi-1.3.4-gcc-4.4.2/bin/mpirun -np 3 --mca mpi_yield_when_idle 1 ./master
> nbock 20795 96.7 0.0 159096 3896 pts/2 R+ 08:11 1:10 ./master
> nbock 20796 0.0 0.0 158960 3804 pts/2 S+ 08:11 0:00 ./master
> nbock 20797 0.0 0.0 158960 3804 pts/2 S+ 08:11 0:00 ./master
> nbock 20813 88.1 0.0 158964 3892 pts/2 R+ 08:12 0:08 ./slave arg1 arg2
> nbock 20814 86.9 0.0 158964 3908 pts/2 R+ 08:12 0:08 ./slave arg1 arg2
> nbock 20815 87.5 0.0 158964 3900 pts/2 R+ 08:12 0:08 ./slave arg1 arg2
>
> nick
>
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