7 Replies Latest reply on Sep 27, 2016 12:23 AM by Abhijeet_3102

    Maximum core CPU usage on ESXI server

    Abhijeet_3102 Lurker

      I am using vsphere 5.5.0. I have one ESXI host with 2 socket , 8 core , hyperthred . I have total 16 Core CPU. I have 6 virtual machines on this EXSI host with 2 core CPU each. So i left with 4 core CPU. One of my virtual machine utilizing more CPU so i want to increase its core CPU.How many more CPU can i assign to this machine. ? Can i assign all rest of 4 core CPU to it to make this machine with 6 core CPU?.Is it possible ? Or i can assign only 2 more core CPU to it. If i will assign all rest of 4 core CPU to it will it have any issue or side effect ?

        • 1. Re: Maximum core CPU usage on ESXI server
          a.p. Guru
          vExpertCommunity WarriorsUser Moderators

          Welcome to the Community,

           

          the physical cores do not necessarily limit the virtual CPUs which can be assigned to the VMs. You can easily overcommit vCPUs unless the VMs are running high CPU loads.

           

          André

           

          PS: Please don't post the same question in multiple forums. I removed these duplicate posts.

          • 2. Re: Maximum core CPU usage on ESXI server
            Abhijeet_3102 Lurker

            Thanks for your reply.

             

            Could you explain in lil brief.

             

             

            I have left with 4 core CPU and i want to increase number of core vCPU to a virtual machine because of its high load. So can i assign all the rest 4 core vCPU to this virtual machine ? should i leave few core vCPU unused.

            • 3. Re: Maximum core CPU usage on ESXI server
              a.p. Guru
              vExpertCommunity WarriorsUser Moderators

              With your hardware "ESXI host with 2 socket , 8 core , hyperthred " the ESXi host has a total of 32 logical available.

              So you could basically - although this will most likely make no sense - assign 32 vCPUs to each VM. The important part is the overall CPU load/usage on the host. The vCPUs which are assigned to a VM are usually not used 100%. So the ESXi host has CPU cycles available to distribute to other VMs.

              The rule of thumb is to assign just as many vCPUs as needed, and monitor the host's CPU usage.

              For details see e.g. https://pubs.vmware.com/vsphere-55/topic/com.vmware.ICbase/PDF/vsphere-esxi-vcenter-server-55-resource-management-guide.…


              André

              • 4. Re: Maximum core CPU usage on ESXI server
                Abhijeet_3102 Lurker

                Dear Andre ,

                 

                Thanks again for your valuable information.

                 

                But i am working in a data center . Where the requirement and configuration (2vCPU to 1 VM) given by the client.

                 

                Now one of virtual machine utilizing more CPU. Many times CPU utilization goes over 99%. This is window server 2012 R2 machine. This machine is utilization more CPU because of SQL server running on this machine.

                 

                So we are planning to increase the vCPU on this machine. Esxi host left with 4 core vCPU (unused).

                 

                Now i have following concern.

                 

                1) Will increase in vCPU on this window machine resolve the high CPU utilization issue.

                2) As I am left with 4 core vCPU . So do I need to assign all rest 4 more vCPU to this machine to make it's  vCPU 6 or I need to assign 2 more vCPU to this machine to make it's total 4 vCPU .

                3) What impact this increase in %CPU utilization could have on this machine. Like hang or crash.

                4) How i can reduce the CPU utilization on this Window machine.

                 

                Could you please guide me for the same.

                 

                Thanks & Regards,

                Abhijeet

                • 5. Re: Maximum core CPU usage on ESXI server
                  a.p. Guru
                  Community WarriorsvExpertUser Moderators

                  But i am working in a data center . Where the requirement and configuration (2vCPU to 1 VM) given by the client.

                  As a system engineer it's probably on you to provide recommendations to your client in order to ensure hassle-free operation.

                  1) Will increase in vCPU on this window machine resolve the high CPU utilization issue.

                  It depends on the workload's requirements. However, if you are seeing high COU usage (without high memory usage too), increasing the vCPU count should at least help.

                  2) As I am left with 4 core vCPU . So do I need to assign all rest 4 more vCPU to this machine to make it's  vCPU 6 or I need to assign 2 more vCPU to this machine to make it's total 4 vCPU .

                  I'd start with adding 2 more vCPUs (e.g. configure 2 dual-core vCPUs for the VM). If you still experience high CPU load after that, you may consider to increase the resources again.

                  3) What impact this increase in %CPU utilization could have on this machine. Like hang or crash.

                  Assuming your are talking about the host, check the current CPU load to see whether there are free resources. With sufficient free resources you shouldn't experience any issues.

                  4) How i can reduce the CPU utilization on this Window machine.

                  You'd first have to find out what causes the high load. If it is caused by badly coded applications, or bugs, you may be able to reduce the load by fixing these issues. If it's however cause due to regular access by many people, your options are basically limited, i.e. you need to increase the resources as required by the application.

                   

                  André

                  • 6. Re: Maximum core CPU usage on ESXI server
                    Abhijeet_3102 Lurker

                    Dear Andre ,

                     

                    Thanks a ton for such valuable information.

                     

                    Please find the below concerns.

                     

                    1) On ESXI host we have total 16 Core CPU. We are already assigned 12 CPU to 6 virtual machine(2 CPU to each VM) already. We have left with 4 Core CPU.My main concern is that do we have any limit on ESXI host about the maximum no of CPU that we can use ? As we have 4 Core CPU left so do we have any limit like we can only use 2 more CPU out of 4 to vritual machine or we can use rest of all 4 CPU and assign to a virtual machine on that ESXI host.

                     

                    2) We have assigned 4 Core CPU to a Linux machine and its load average goes few time above 4 for 1, 5 . 15 minutes as well CPU utilization above 99 % . What should we do to reduce it. What all precaution we should take for this. What all impact can we face because of this high load and high CPU utilization.

                     

                    Thanks & Regards,

                    Abhijeet

                    • 7. Re: Maximum core CPU usage on ESXI server
                      Abhijeet_3102 Lurker

                      Dear Andre ,

                       

                      Thanks a ton for such valuable information.

                       

                      Please find the below concerns.

                       

                      1) On ESXI host we have total 16 Core CPU. We are already assigned 12 CPU to 6 virtual machine(2 CPU to each VM) already. We have left with 4 Core CPU.My main concern is that do we have any limit on ESXI host about the maximum no of CPU that we can use ? As we have 4 Core CPU left so do we have any limit like we can only use 2 more CPU out of 4 to vritual machine or we can use rest of all 4 CPU and assign to a virtual machine on that ESXI host.

                       

                      2) We have assigned 4 Core CPU to a Linux machine and its load average goes few time above 4 for 1, 5 . 15 minutes as well CPU utilization above 99 % . What should we do to reduce it. What all precaution we should take for this. What all impact can we face because of this high load and high CPU utilization.

                       

                      Thanks & Regards,

                      Abhijeet