Determining if multiple virtual CPUs are causing performance issues

You may experience these performance issues with a multiple CPU virtual machine running on an ESX host:

  • Poor transfer speeds when copying data to or from a virtual machine
  • Backup jobs time out or are very slow
  • A virtual machine performs poorly

To determine if multiple vCPUs assigned to your virtual machine is causing poor performance:

  1. Open a console prompt on the ESX host or initiate an SSH connection to it.
  2. Type esxtop and press Enter.
  3. On the CPU screen, check the %CSTP value. If this number is higher than 100, the performance issues may be caused by the vCPU count. Try lowering the vCPU count of the virtual machine by 1.

Note: The %CSTP value represents the amount of time a virtual machine with multiple virtual CPUs is waiting to be scheduled on multiple cores on the physical host. The higher the value, the longer it waits and the worse its performance.  Lowering the number of vCPUs reduces the scheduling wait time.



About PiroNet

Didier Pironet is an independent blogger and freelancer with +15 years of IT industry experience. Didier is also a former VMware inc. employee where he specialised in Datacenter and Cloud Infrastructure products as well as Infrastructure, Operations and IT Business Management products. Didier is passionate about technologies and he is found to be a creative and a visionary thinker, expressing with passion and excitement, hopefully inspiring and enrolling people to innovation and change.
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