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How to set-vcpu 8 threads - 1 each from 8 cores

Hi, we are licensed for 8 "Solaris CPUs" and we have a whole SPARC T8-1 to run on. T8-1 has one socket, 32 cores and 8 threads per core i.e. in Solaris terms that's 256 CPUs.

If I do >ldm set-vcpu 8 mydomain

then I am pretty sure it will allocate the first 8 threads, which are all on the same core.

However, if there were a way to allocate 1 thread off each of the first 8 cores, then my app might run faster?

So I'm thinking, what about this:

>ldm set-vcpu 1 mydomain

>ldm set-vcpu 7 unuseddomain

>ldm add-vcpu 1 mydomain

>ldm add-vcpu 7 unuseddomain

>ldm add-vcpu 1 mydomain

>ldm add-vcpu 7 unuseddomain

>ldm add-vcpu 1 mydomain

>ldm add-vcpu 7 unuseddomain

>ldm add-vcpu 1 mydomain

>ldm add-vcpu 7 unuseddomain

>ldm add-vcpu 1 mydomain

>ldm add-vcpu 7 unuseddomain

>ldm add-vcpu 1 mydomain

>ldm add-vcpu 7 unuseddomain

>ldm add-vcpu 1 mydomain

>ldm add-vcpu 7 unuseddomain

a) Will that get mydomain 8 threads, each one from a separate core?

b) Does that have the potential to run faster than 8 threads from a single core?

c) Can I/should I follow it up with >ldm set-mau 8 mydomain ?

Thanks, Jim

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Answers

  • Jens
    Jens Member Posts: 91 Blue Ribbon
    edited Jan 17, 2019 12:31PM

    Interesting question.

    I hope to see some informed answers from the big guys ;-)
    I'd assume that the placement algorithm will outsmart that approach and keep ressources local to avoid trashing but that might be entirely false or depend on whatever (e.g. ldm version). For fun, I'd check with two bound ldoms. In either case I'd prepare for things being unstable in config space as I am not aware of a vcpu id in the config that might keep such a partition in place across reboots, migrations etc.

    If ressources remain unused and license permits, you might look into adding whole cores to your domain and limit thread usage at that level, e.g. disabling and/or assigning cpus to zones or alike.

    Are you positive, that your license is based on solaris cpus and not cores? Any hardpartitioning requirement or similar topic that need to be taken into account?

  • Nik
    Nik Blocked Member Posts: 2,879 Bronze Crown
    edited Jan 17, 2019 3:21PM

    Hi.

    Oracle have rules for confugure  LDOM according license policy.

      https://www.oracle.com/technetwork/server-storage/vm/ovm-sparc-hard-partitioning-1403135.pdf

    In other cases You can have quiestions about  license rules.

    Regards,

      Nik