Specification of island_count on SuperMUC

LRZ aktuell publish at lrz.de
Mo Jan 14 12:57:26 CET 2013

For Jobs with a core count of more than 512 you must specify the
 island_count in your LoadLeveler job. The LoadLeveler syntax is:
 #@ island_count = min,max    or
 #@ island_count =  number
 The scheduler attempts to start the job on min islands, but will start
 the job on up to max islands if the job does currently not fit on min
 islands (e.g., because there are not enough free nodes available).
 Since SuperMUC has a pruned (1:4) network topology, there is a
 trade-off between performance and more chances to get a job allocated.
 LRZ recommends to use an island count which is slightly higher (+1 or
 +2)than the minimum requirement to give the LoadLeveler more
 flexibility for finding free nodes.
 Example: if you want to run on 2000 nodes, you must use at least 4
 islands. In this case specify
 #@ island_count = 4,5
 instead of just requiring just 4 islands.
 For jobs with less than 512 you can also use island_count. But always
 specify a minimum island_count of 1 to avoid a fragmentation of the
 machine by small jobs.
 see: http://www.lrz.de/services/compute/supermuc/loadleveler/#
 JCF.keywords for details.

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 Matthias Brehm

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