Logical Processor Usage

Omer Faruk GUMUS_21691
Omer Faruk GUMUS_21691 Altair Community Member
edited October 2020 in Community Q&A

Hi,

While explicit analysis, I could get one A000 File per 10 minutes once used 4 core , however, I could get one A000 file per 14 minutes once used totally 8 core (+4 logical processors) .

How much I increase the logical core numbers, getting A000 animation files speed is getting slower.
 

Another computer we used have totally 72 core ( 36 of 72 are logical processor) has same situation when we include the logical processor in radioss as -nt ..

Dou you have any suggestion to speed up our explicit analysis when we would like to use logical processor in PC ? ,

 

Thanks in advance.

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Answers

  • Pranav Hari
    Pranav Hari Altair Community Member
    edited March 2019

    Hi Omer Faruk GUMUS

     

    Normally it is recommended to set the number of SPMD domains (np) equal to the number of sockets and to set the number of SMP threads (nt) equal to the number of cores per socket.

    With a low number of cores (below 32), a pure SPMD run might be more effective but the performance gap should be small.

    With a very high number of cores (1024), it is possible to increase the number of SMP threads up to the number of cores per node and set only one SPMD domain per node to maximize performance if the limit of scalability of the interconnect network is reached

     

    Check this document and also refer to the Radioss parallelism topic (page 47) discussed in the e-book https://altairuniversity.com/free-ebooks-2/free-ebook-crash-analysis-with-radioss-a-study-guide/

     

     

     

    Unable to find an attachment - read this blog

  • Andy_20955
    Andy_20955 New Altair Community Member
    edited March 2019

    Hi,

    First some definitions. 

    From https://superuser.com/questions/1105654/logical-vs-physical-cpu-performance

    The concept of cores is not that simple. Logical cores are the number of Physical cores times the number of threads that can run on each cores. This is known as HyperThreading. If I have a computer that has a 4-core processor, runs two threads per core, then I have a 8 logical processors.

     

    In Radioss, we typically recommend using only physical cores where you set the number of physical cores  = -np option.    So if you have a machine with 4 physical cores using

    -np 4.  You should get a small amount of speed up by using the extract Hyperthreading cores by using, -np 4 -nt 2. 

     

    Or for your other machine with 36 physical cores use, -np 36.  or you can try -np 36 -nt 2 if you want to use all 72 logical cores but the speedup will be not very large.  Meaning it won't run 2x faster when using all 72 logical cores. 

     

    Thanks,

    Andy

     

  • QuyNguyenDai
    QuyNguyenDai Altair Community Member
    edited March 2019

    I don't know about Radioss. But for almost FE software, like Ansys, Abaqus, Nastran, Samcef,... Intel Hyperthreading feature don't give advantage. Every computing server should disable HT in BIOS. That's the way we do for all server of GDTech.

     

  • GAJENDRA KUMAR NHAICHANIYA
    GAJENDRA KUMAR NHAICHANIYA Altair Community Member
    edited April 2019

    Hello @Andy,

    Thanks for valuable information. As i understood -nt 2 unable Hyper-threading. Am i right ?

     

    Hello to all,

    Apart from i want to ask

    1. In my PC i have 2 socket 6 core each. By simply providing -np 12 can i use all cores ? Or i need to input something else ?

    2. default -nproc command also given in Hyperform module. Is it same as -np ?

    3. Always i got warning as -

    WARNING ID :          762
    ** WARNING : -nthread COMMAND LINE OPTION USED AND /SPMD CARD SET
    DESCRIPTION :  
       WHEN -nthread COMMAND LINE OPTION IS USED AND NTHREAD IS SET IN /SPMD
       /SPMD SETTING IS IGNORED

     

    Here what is SPMD & why this warning appears ?

    Thanks. 

     

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