SuperMUC: Change in Energy Policy on Thin islands

[LRZ aktuell]

Dear users of the SuperMUC Petaflop System at LRZ,
 
 with recent updates to LoadLeveler, new features have become available
 that support an improved energy savings model on the thin islands of
 the system. As a consequence, you will in the near future need to
 modify your Loadleveler scripts if you wish to run your thin node jobs
 at a higher frequency than the standard value of 2.3 GHz.
 
 There are two required items you need to enter in all your LoadLeveler
 scripts:
 
  1. You need to generate an energy tag for your job using the
     #@ energy_policy_tag = <tag name>
     notation; this energy tag will after the first run of that job
     contain the information Loadleveler needs to estimate whether a
     performance advantage can be gained at sufficiently low cost.
  2. You need to specify the keyword
     #@ minimize_time_to_solution = yes
     to request a frequency increase from LoadLeveler. Without this
     item, all jobs will run at the standard frequency of 2.3 GHz.
 
 If both the above are fulfilled, LoadLeveler will set the CPU frequency
 for all nodes of the job according to following criteria, applied in
 order of appearance:
 
   * If run time using 2.4 GHz is expected to decrease by more than 2.5%
     compared to 2.3 GHz, the frequency is set to 2.4 GHz
   * If run time using 2.5 GHz is expected to decrease by more than 5%
     compared to 2.3 GHz, the frequency is set to 2.5 GHz
   * If run time using 2.6 GHz is expected to decrease by more than 8.5%
     compared to 2.3 GHz, the frequency is set to 2.6 GHz
   * If run time using 2.7 GHz is expected to decrease by more than 12%
     compared to 2.3 GHz, the frequency is set to 2.7 GHz
 
 This new energy management policy will be activated on October 7, 2013
 at 10:00 am. We encourage all users of the system to make use of this
 new feature to accelerate processing of jobs.
 
 Please note that after this change, the previously supported keyword 
 max_perf_decrease_allowed will not have any effect any more; jobs still
 using this keyword will be rejected at submission time from January
 2014 onward. For further details, please also consult http://www.lrz.de
 /services/compute/supermuc/loadleveler/#energy which will be updated on
 the same date the change is performed.


 This information is also available on our web server
 http://www.lrz-muenchen.de/services/compute/supermuc/aktuell/ali4667/

 Reinhold Bader