On Wed, 9 Jun 2004, Richard Hadsell wrote:
> I'm trying to use LAM 7.0.6 and haven't been able to find the answer to
> this question in the user's guide or in the man pages. What is the
> default RPI module, if you don't use any -ssi rpm option with mpirun?
> (My laminfo says that I have crtcp, lamd, sysv, tcp, and usysv
> available.)
The answer is: it depends. :-)
Each module has a different selection criteria and a different priority.
In general, the "best" module will typically be selected. The default
priorities are:
-----
shell$ laminfo -param rpi all | grep priority
SSI rpi: parameter "rpi_crtcp_priority" (default value: "25")
SSI rpi: parameter "rpi_lamd_priority" (default value: "20")
SSI rpi: parameter "rpi_sysv_priority" (default value: "30")
SSI rpi: parameter "rpi_tcp_priority" (default value: "20")
SSI rpi: parameter "rpi_usysv_priority" (default value: "40")
-----
In most cases, all of the modules will be *available* (i.e., if you have
shared memory). Hence, LAM will take the union of all the available
modules from all processes and then take the one with the highest
priority.
So in most cases, it will be usysv.
Check the user docs -- note that if you use usysv and you oversubscribe
your node (i.e., run more procs than CPUs), your performance may be
horrible because usysv uses spin locks. In such circumstances, sysv would
probably be better.
--
{+} Jeff Squyres
{+} jsquyres_at_[hidden]
{+} http://www.lam-mpi.org/
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