about sh-mem mechanism

[Pete Wyckoff]

jlgr at super.unam.mx said:
>  how can i disable shared mem communications between process in
>  a SMP node?
> 
>   by the way, why mpiexec uses shmem by default in SMP nodes? i think
>   most people uses sockets. indeed, i think there is no performance
>   gain by using shmem vs. sockets (a parallel program is as fast as its
>   slowest process).

That's interesting to hear.

I thought the consensus was that you want to use shmem inside an SMP,
but have not done any performance tests myself.  Show me some plots
sometime, if you can motivate someone to do the data collection.

You can rebuild your mpich-p4 to turn this off, then recompile mpiexec
so it doesn't try to tell p4 to do shmem jobs:

    ./configure --with-default-comm=p4 --disable-p4-shmem

Unfortunately there seems to be no way dynamically to tell mpich how
to start up the code.  So you as sys admin have to decide and compile
both mpich and mpiexec so that they match.

		-- Pete