[mvapich-discuss] mvapich & mpiexec

[Matthew Koop]

> With Jan's encouragement and testing, we may have working support
> for mvapich 0.9.9 in mpiexec.  It is a more complex change than we
> had imagined.

Good to hear that support is now in mpiexec and appears to be working.

> Before I check it in, can you provide some commentary on the reason
> for the two sets of accept(), read(), write() for every task?  On
> the surface this would seem like a major barrier to scalability.
> There must be a good reason to get the hostids out first, then have
> the tasks come back for the addresses.

The reason here to allow extended functionality. Information
about process/host pairs are exchanged prior to QP setup in order to allow
QPs to be setup in efficient ways. In particular, if multiple HCAs are
available, QPs should utilize them efficiently. Also, knowing the ranks on
a single node allows better use of multiple paths through the network --
all of this is required before QP setup.

Scalability has not been a problem and has been extended to multi-thousand
processes.

Thanks again for adding support to mpiexec.

Matt