LS Dyna

LS Dyna

Topics relate to LS-DYNA, Autodyn, Explicit STR and more

Unable to use 32 out of 40 logical processors to run sim

    • Veronique Bouvette


      I have a bunch of simulations to run (628 simulations). After bench marking test, I reached the conclusion that best parameters are:

      • mpp
      • -np20 (but not big difference with -np16, over -np24 = slow) - I have 256,835 elements so around 10k to 15k elements per processors seem to be the most efficient
      • double precision (since time increased is not significant with single precision)

      In order to be as efficient as possible, I tried running 2 simulations at the same time at -np16 each, but it dosen't work (I tried running 2 simulations at -np 12 and it worked fine, but is slow and is not efficient). 

      I don't understand why this won't work (to use -np16 + -np16) since I have 40 available logical processors on the computer.

      I work on windows!

      THANK YOU!

    • VJ
      Ansys Employee

      Hello Veronique,

      Hyperthreaded cores are not supported by Ansys applications and will not provide performance boost. You have 20 physical cores, which is the max number of cores the applications will use. 

      Refer 3.1.3 -

      Refer -



      • Veronique Bouvette

        Thank you for your answer! I still don't understand since -np XX attributes job on logical processors (not on physical like you said). If I run 2 simulations at the same time using -np 10 for each, about 60% of cpu is used (20/40 = 50% plus 10% for my system). CPU usage always matches -np XX on total logical processors (40) and not physical processors (20). 

        Help me understand this please!

    • Loic Ivaldi
      Ansys Employee
      For your processor, have a look here :
      The line of interest is "Total cores"
      I don't know much regarding your configuration but if you use MS-MPI you can try the following command :
      mpiexec -np 10 -aa -a "path_of_the_solver" i=input.k memory=
      Deactivate hyperthread in the BIOS.
      Best Regards,
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