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OL5.8 OVM Guest number of CPU´s

tbrinkmann Explorer
Currently Being Moderated
Hi,
does anyone can help we understand if it is possible and a good idea to configure more virtual CPU´s
in a OVM Guest as cores integrated in the physical hardware.

We have a 2 cpu 6 core OVM hardware and try to configure 20 virtual cpu´s in ONE guest system.

I don´t like that idea....

Thanks *T                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
  • 1. Re: OL5.8 OVM Guest number of CPU´s
    Dude! Guru
    Currently Being Moderated
    http://www.oracle.com/technetwork/server-storage/vm/ovm-hardpart-168217.pdf

    Each core is a physical CPU. The idea to bind a CPU to a VM is to prevent the software from running on physical cores other than the ones specified. In such a case, virtual machines are configured with dedicated CPU resources instead of the default of resource scheduling, which is to use all available CPUs of the server.

    You don't even have 20 CPU's, only 12, unless you count in hyperthreading, which divides one CPU into 2 logical CPU's for better resource handling.

    OL5.8 as far as I know supports any number of CPU's.
  • 2. Re: OL5.8 OVM Guest number of CPU´s
    Avi Miller Guru
    Currently Being Moderated
    tbrinkmann wrote:
    does anyone can help we understand if it is possible and a good idea to configure more virtual CPU´s
    in a OVM Guest as cores integrated in the physical hardware.
    No, it's not.
    We have a 2 cpu 6 core OVM hardware and try to configure 20 virtual cpu´s in ONE guest system.
    Assuming you have hyperthreading, you actually have 24 pCPUs on this system (2 sockets, 6 cores/socket, 2 threads/core = 2 x 6 x 2 = 24) so you can actually assign 20 vCPUs to a guest and still be under your pCPU count.
  • 3. Re: OL5.8 OVM Guest number of CPU´s
    Dude! Guru
    Currently Being Moderated
    With the arrival of the Core 2 processor, Hyper-Threading disappeared. But Intel decided to resurrect it with the Nehalem micro-architecture, which is the basis for all Core i7, i5, and i3 CPUs available today, including the just-released six-core Core i7-980X.
  • 4. Re: OL5.8 OVM Guest number of CPU´s
    tbrinkmann Explorer
    Currently Being Moderated
    ..So xm info told me that

    release : 2.6.18-128.2.1.4.44.el5xen
    version : #1 SMP Thu Nov 10 22:05:12 EST 2011
    machine : i686
    nr_cpus : 16
    nr_nodes : 1
    cores_per_socket : 4
    threads_per_core : 2

    So we have 16 cores inclusive Hyper-Threading or 16 cores *2 ?
    ______________________________
    cat /proc/pcuinfo

    rocessor     : 15
    vendor_id     : GenuineIntel
    cpu family     : 6
    model          : 44
    model name     : Intel(R) Xeon(R) CPU E5640 @ 2.67GHz
    stepping     : 2
    cpu MHz          : 2665.912
    cache size     : 12288 KB

    I´m confused :-/

    Oracle Support told us to set the vCPU´s to 20 because of we have 10 intances on on OVGuest....

    Thanks *T                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
  • 5. Re: OL5.8 OVM Guest number of CPU´s
    Avi Miller Guru
    Currently Being Moderated
    tbrinkmann wrote:
    nr_cpus : 16
    nr_nodes : 1
    cores_per_socket : 4
    threads_per_core : 2
    This doesn't match what you said in the original post: this machine is a single-socket, quad-core hyperthreaded machine (1x4x2 = 16). So you have 16 pCPUs on this server.
  • 6. Re: OL5.8 OVM Guest number of CPU´s
    tbrinkmann Explorer
    Currently Being Moderated
    Re,
    sorry, yes you are right not a six core..only 4 cores.

    But this a two socket machine. I check the HP ilo board.

    2x4xhyper(2) = 16...

    *T                                                                                                                                                                                                                                                                                                           
  • 7. Re: OL5.8 OVM Guest number of CPU´s
    Avi Miller Guru
    Currently Being Moderated
    tbrinkmann wrote:
    sorry, yes you are right not a six core..only 4 cores.
    Run this:
    # xenpm get-cpu-topology
    It will tell you exactly how many threads/cores/sockets you have.
  • 8. Re: OL5.8 OVM Guest number of CPU´s
    tbrinkmann Explorer
    Currently Being Moderated
    Re,
    CPU     core     socket
    CPU0     0     0
    CPU1     0     1
    CPU2     10     0
    CPU3     10     1
    CPU4     1     0
    CPU5     1     1
    CPU6     9     0
    CPU7     9     1
    CPU8     0     0
    CPU9     0     1
    CPU10     10     0
    CPU11     10     1
    CPU12     1     0
    CPU13     1     1
    CPU14     9     0
    CPU15     9     1

    But I really do not understand why the oracle support told us to configure 20 vcores ;-(
    We still waiting for an update from OSupoort

    Do you ever heart about to configure 2 vCPUs´ for each instance running on a OMV Guest ?
  • 9. Re: OL5.8 OVM Guest number of CPU´s
    Avi Miller Guru
    Currently Being Moderated
    tbrinkmann wrote:
    But I really do not understand why the oracle support told us to configure 20 vcores ;-(
    I don't either. The maximum vCPUs you should configure in a single guest is 16.
    Do you ever heart about to configure 2 vCPUs´ for each instance running on a OMV Guest ?
    I'm not sure I understand the question here. You can over-commit vCPUs, i.e. you can have multiple guests all with 16 vCPUs and Oracle VM with handle the scheduling accordingly. But there is no benefit from configuring more vCPUs than you have pCPUs.
  • 10. Re: OL5.8 OVM Guest number of CPU´s
    tbrinkmann Explorer
    Currently Being Moderated
    Avi Miller wrote:
    tbrinkmann wrote:
    But I really do not understand why the oracle support told us to configure 20 vcores ;-(
    I don't either. The maximum vCPUs you should configure in a single guest is 16.
    Do you ever heart about to configure 2 vCPUs´ for each instance running on a OMV Guest ?
    I'm not sure I understand the question here. You can over-commit vCPUs, i.e. you can have multiple guests all with 16 vCPUs and Oracle VM with handle the scheduling accordingly. But there is no benefit from configuring more vCPUs than you have pCPUs.
    I understand the behave about vcores and single or multiple VMGuest and max cpu amount now.

    This is may a db related question the support told us to configure 2 vCPU´s for each instance that is running on a single vmguest. Does anyone have a prove of this ?
  • 11. Re: OL5.8 OVM Guest number of CPU´s
    Dude! Guru
    Currently Being Moderated
    I don't understand the logic in configuring more CPU's than physically available. Whether or not your system will benefit from HT depends on on use and application. Each process can only run on one physical or logical CPU. If you have multiple processes they can run on a different CPU or logical CPU, depending on workload. I'm not aware of any best practices here - I suggest to let the system decide what to do. So to configure multiple CPU's for a database server certainly makes sense since Oracle uses several processes. Whether or not you're better off with 2, 4 or 8, how knows. You need to monitor the system to determine if CPU is your bottleneck. Why bother to partition the hardware and possibly limit available resources.
  • 12. Re: OL5.8 OVM Guest number of CPU´s
    tbrinkmann Explorer
    Currently Being Moderated
    ...yeah dude you are absolutely right. I will post the anthers from the oracle support it does not make any sens to configure more cpu´s as physical available.

    Thanks *T                                                                                                                                                                                                                                                                                                                                                       
  • 13. Re: OL5.8 OVM Guest number of CPU´s
    Dude! Guru
    Currently Being Moderated
    There might just be some misunderstanding in regard to what CPU is in your system. Unless you have an Oracle license restriction, I would see no compelling technical reason to partition the hardware.
  • 14. Re: OL5.8 OVM Guest number of CPU´s
    tbrinkmann Explorer
    Currently Being Moderated
    ...... from oracle support     
    Hi,

    The OVM Hardware is a two processor system with 4 cores in each processor.
    Do you think we have to configure 19 virtual processors to the OL vm guest ?
    Ans) Yes, please configure 19 virtual processors to accommodate currently running 9 databases

    Does it is a good idea to configure more virtual processors as we have cors / processors in the hardware ?
    Ans) Yes, please configure more virtual processors.

    ...*T
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