[mvapich-discuss] process limits

[Dhabaleswar Panda]

Hi Mark, 

>     Is there an effective or hard limit on the number of MVAPICH
>     processes that can be run on a single node?
>
>     Given N cpus, each having M cores, on a single node, I've been told
>     that one can not run more than N*M MVAPICH processes on a single
>     node.  In fact, I observe that if I try to even approach this number
>     with "-np 16" (for a node with N=8 and M=4), I observe a "unable to
>     find child nnnn!" or "Child died" message.  Is this a configuration
>     problem with this system or somehow an expected behavior?

Not sure why you are getting this error. We have run applications with
N*M MVAPICH processes with N CPUs each having M cores (N=2, M=4; N=4,
M=2).

Can you provide more details on the system configuration, the MVAPICH
version you are running and the interface you are using (Gen2, uDAPL,
shared memory, etc.).

>     More pointedly, should oversubscription of cores, np > N*M, on a
>     single node work in MVAPICH?  How about in MVAPICH2?

Yes, oversubscription should work for both MVAPICH and
MVAPICH2. However, for oversubscription to work, you need to use the
`blocking' mode of operation, not `polling' mode (which is the normal
mode of operation to get the best performance).  This is typical for
any MPI design. MVAPICH 0.9.9 supports `blocking' mode. The latest
version of MVAPICH2 (1.0-beta, soon we will have the final version)
also supports `blocking' mode. Please take a look at the respective
user guides to see how to use the `blocking' mode.

Thanks, 

DK


>             regards,
> -- 
> ***********************************
>  >> Mark J. Potts, PhD
>  >>
>  >> HPC Applications Inc.
>  >> phone: 410-992-8360 Bus
>  >>        410-313-9318 Home
>  >>        443-418-4375 Cell
>  >> email: potts at hpcapplications.com
>  >>        potts at excray.com
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