The user may also set the KMP Offset, which is the core offset for the current run. The KMP Offset relates to the number of cores already being used by the system, and is therefore usually set to zero. The KMP Offset should only be adjusted if the user wishes to run more than one model on the same machine. In order to run second model the KMP Offset should be set to the number of cores being used in the already running model. For example, assume a system comprising a Xeon Processer with 6 cores (12 threads), is already running a model on 2 cores (where KMP Offset had been set to 0). If the user wishes to run a second model, they then should set the KMP Offset to 2 and the OMP threads to 4.
A typical Intel I7 computer had from has 4 to 6 cores. The way these cores are handled in the EFDC code is with the KMP_AFFINITY variable, defined as:
KMP_AFFINITY=[<modifier>,...]<type>[,<permute>][,<offset>]
For example, to list a machine topology map, specify "KMP_AFFINITY=verbose,none" to use a modifier of verbose and a type of none.
"KMP_AFFINITY = granular = fine, compact, 1,0", will assign individual threads to different cores. When it assigns the threads it also spreads them out. If the modifier is set to verbose, then a map of threads will also be produced.
Note that a "0_RunEFDC" file is created in the model folder each time the EFDC_DSI model is run. This file tells EE whether the model ran to completion or not as it is deleted on successful model completion.. If the user opens that file then they can see these parameters.
Figure 1 illustrates the binding of OpenMP thread to hardware thread contexts when specifying "KMP_AFFINITY=granularity=fine,compact".
Figure 1 Open MP thread IDs (graphic courtesy of Intel).
To learn more about the KMP_AFFINITY environment and the specific syntax which must be used please visit the following website:
http://software.intel.com/sites/products/documentation/hpc/composerxe/en-us/cpp/mac/optaps/common/optaps_openmp_thread_affinity.htm