[Beowulf] Intel MPI 2.0 mpdboot and large clusters, slow tostart up, sometimes not at all

[M J Harvey]

Hello,

> We are going through a similar experience at one of our customer sites.
> They are trying to run Intel MPI on more than 1,000 nodes.  Are you
> experiencing problems starting the MPD ring?  We noticed it takes a
> really long time especially when the node count is large.  It also just
> doesn't work sometimes.

I've had similar problems with slow and unreliable startup of the Intel 
mpd ring. I noticed that before spawning the individual mpds, it 
connects to each node and checks the version of the installed python 
(function getversionpython() in mpdboot.py). On my cluster, at least, 
this check was very slow (not to say pointless). Removing it 
dramatically improved startup time - now it's merely slow.

Also, for jobs with large process counts, it's worth increasing 
recvTimeout in mpirun from 20 seconds. This value governs the amount of 
time mpirun waits for the secondary mpi processes to be spawned by the 
remote mpds and the default value is much too aggressive for large jobs 
started via ssh.

Kind Regards,

Matt