7 Replies Latest reply on Oct 3, 2009 2:47 PM by jbogardus

    4 vCPUs problem?

    snikers Novice





      In attached file there is a description of CPUs



      When i create a VM with 4 cores i`ve got  something abnormal. The vCPU load goes up to 90-100%, but on Guest OS (Windows server 2003 x86 Enterprise) nothing is running. Such situation is on these CPUs Intel Xeon 5030 and Intel Xeon E5410 CPUs. 



      Can somebody detaily explain this?



      Thank you



        • 1. Re: 4 vCPUs problem?
          sflanders Master
          VMware EmployeesvExpert

          Have you tried with less vCPU and if so what were the results? You are noticing the spiked vCPU from the VI Client? Do you notice it on power on only or does it always remain high?

          • 2. Re: 4 vCPUs problem?
            snikers Novice

            1) Haven`t try, and not going to try as i should provide normal 4 vCPU VM



            And i can say that other 8 VM work well 



            2)   "noticing the spiked vCPU"- don`t understand what you mean




            3)  Not when i power on... it becomes time-to-time 50%, 90-100% loaded after some hours of work, now it stays 30% load for more then an hour

            • 3. Re: 4 vCPUs problem?
              asatoran Champion
              snikers wrote:

              1) Haven`t try, and not going to try as i should provide normal 4 vCPU VM...And i can say that other 8 VM work well...


              You don't give much details of your host and guests, so it's hard to say why the other VMs "work well."  Do the other VMs have 4 vCPUs allocated to them as well?  And are they all running at the same time on the same host?  If so, then you may be running into CPU scheduling issues, which is why it was suggested you reduce your vCPUs.  Take a look at this VROOM! blog and this document for more info.  In general, unless you have apps that can actually use the extra vCPUs, it doesn't help performace and could hurt performance.  (e.g.: MS-SQL server.)

              • 4. Re: 4 vCPUs problem?
                weinstein5 Guru

                The issue is this is not an ideal design to host a VM with 4 vCPUs - best practice is you want at least two timea the number of cores than the number of vCPUs in the VMs - you current setup ony has four cores but best practice should be 8 cores - this will cause an abnormal spike in vCPU utilization because how the vCPUs get scheduled to the physical cores -





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                • 5. Re: 4 vCPUs problem?
                  devzero Master

                  >but on Guest OS (Windows server 2003 x86 Enterprise) nothing is running.

                  at least, the OS , some drivers and some services are running.

                  did you check for cpu usage in %kernel (instead of %usr) ?

                  (red line in taskmanager, need to add that from the menu)

                  • 6. Re: 4 vCPUs problem?
                    snikers Novice


                    As soon as instead of 4 vCPU used 2 - everything goes Ok. That`s wierd, then what for is 4 vCPU possibility?..



                    • 7. Re: 4 vCPUs problem?
                      jbogardus Expert


                      For when people have systems with more cores and applications that really need the extra processing power.  These days having 2 Quad Core processors if fairly typical and having more than 8 cores in a system is not at all uncommon.  Those are situations when using 4 vCPU is a potentially efficient option, when you have 4 physical cores it is not.



                      As previously posted it is discouraged to run more vCPUs than the running application is going to be making good use of because that just takes away CPU time from other VMs without good reason.  Configuring many vCPUs is especially a bad idea when the number of vCPUs is equal to the number of physical cores available.