9 Replies Latest reply on May 5, 2008 1:17 PM by TomHowarth

    Performance of Multi CPU Guests

    RobHeilman Novice

       

      I am using Debian 4.0 (etch) and Ubuntu 7.10 (gutsy) as my geust and host os's, all 32-bit.  Whenever I select multiple CPU's for the guest OS the performance is abismal.  It will lock up on a regular basis during the guest install process.  If I set it to 1 CPU for the guest it works just fine.  I have all debugging turned off and I am allocating anywhere from 512MB to 2GB of memory.

       

      Anyone have any ideas?

       

       

        • 1. Re: Performance of Multi CPU Guests
          Peter_vm Guru

          How many logical CPU's do you have in host?

          • 2. Re: Performance of Multi CPU Guests
            TomHowarth Guru
            vExpertUser Moderators

             

            you have to remember that in a multi CPU Guest, the same number of physical CPU cores to the number of vCPUs in the guest must be available to service a cycle before the  guest can do so.  therefore if you have a quad core Host and a number of Dual vCPU guests, you are in CPU contention.  this is more of an issue in a hosted environment as the Host OS will use all available CPU Cores for its own purposes, and the remainder are available for Guest running.

             

             

             

             

             

            Under ESX the Service Console is tied to CPU0.  this is not the case in Hosted environments.  VMware Server handles CPU scheduling well as can be seen when you are running single vCPU guests.  and it handles CPU scheuling as well as it can when vSMP is being utilised.  unless your Host has a larges amount of cores, ie at least a dual quad core (8 Logical vCPUs)  I would personally not even consider the use of vSMP.

             

             

             

             

             

            if you monitor the Guest via Perfmon you will see High CPU ready time and Context switching. on you SMP enabled guests. this is an indication of CPU contention.

             

             

             

             

             

            Hope that this helps.

             

             

             

             

             

             

             

             

             

             

             

            Tom Howarth

            VMware Communities User Moderator

             

             

            • 3. Re: Performance of Multi CPU Guests
              RobHeilman Novice

               

              I understand that CPU contention should be an issue on a heavily loaded system.  However on a system with a single guest OS and nothing else happening on the host OS this problem rears it's head.  I have been working with two different hosts.  One has dual Opteron 246's (single core per CPU) and  the other has dual Opteron 265HE's (dual core per CPU)

               

               

              Is it possible that the kernel modules for the host need some additional compile time tuning?

               

               

               

              • 4. Re: Performance of Multi CPU Guests
                yackip1 Enthusiast

                 

                i have only seen performance issues when there are two guests (with at least one guest set to 2 cpus) on a host with a single (dual core) machine. my host happens to be a dell poweredge 840 running ubuntu 8.04 (64-bit)

                 

                 

                 

                 

                 

                 

                 

                 

                • 5. Re: Performance of Multi CPU Guests
                  RobHeilman Novice

                  Does it make sense that you can only have as many virtual CPU's as you have physical CPU's/core before a performance crashes to unacceptable levels?  Why even run vmware at that point?  I thought the driving motivation is to drive the hardware to higher utilization levels...not allocate unused "cores."

                  • 6. Re: Performance of Multi CPU Guests
                    RDPetruska Guru
                    vExpertUser Moderators
                    RobHeilman wrote:

                    Does it make sense that you can only have as many virtual CPU's as you have physical CPU's/core before a performance crashes to unacceptable levels? Why even run vmware at that point? I thought the driving motivation is to drive the hardware to higher utilization levels...not allocate unused "cores."

                     

                    No, that is not what anyone is saying.  Virtualizing multiple CPUs in one VM is much more taxing on a host system than virtualizing a single CPU in a VM.  In order for the host OS to have enough resources to go around, it is recommended to only run multi-virtual-CPU guests on hosts with more than 2 physical cores.  You can still run as many guests as you want/can with your resources.

                     

                     

                    And, with the hosted products, the driving motivation for virtualization is NOT higher host hardware utilization levels (typically), but testing of multiple OS's and/or versions, isolation, portability, ease of backup/restore, etc.

                     

                     

                    • 7. Re: Performance of Multi CPU Guests
                      RobHeilman Novice

                       

                      Can you define "hosted" as it referrs to VMWare?  I think I may be getting a little confused by use of that term.  I am starting to think it is in reference to virtualization on top of a gerneral purpose OS where the alternative would be something like ESX?

                       

                       

                      The VMWare hosted seminars I have recently attended have greatly emphasized increasing hardware utilization.  That might be where my disconnect is coming from.

                       

                       

                       

                       

                       

                      • 8. Re: Performance of Multi CPU Guests
                        RDPetruska Guru
                        vExpertUser Moderators
                        RobHeilman wrote:

                        Can you define "hosted" as it referrs to VMWare? I think I may be getting a little confused by use of that term. I am starting to think it is in reference to virtualization on top of a gerneral purpose OS where the alternative would be something like ESX?

                         

                        The VMWare hosted seminars I have recently attended have greatly emphasized increasing hardware utilization. That might be where my disconnect is coming from.

                         

                         

                         

                         

                        Correct - hosted refers to products installed and running (and relying on the resource management of) on top of a Host OS.  VI and/or ESX products are bare metal products, meaning they are completely self-contained - no host OS required.

                         

                         

                        Most VMware seminars are touting the benefits of the VI platform and its product line.

                         

                         

                        • 9. Re: Performance of Multi CPU Guests
                          TomHowarth Guru
                          User ModeratorsvExpert

                          another complicatiing factor is that a machine that runs guests is called a Host.  but a Hosted product relies on an underlying OS as opposed to ESX with installs directly on to a machine.

                           

                           

                           

                           

                          Tom Howarth

                          VMware Communities User Moderator