Tuesday, September 23, 2008

What Causes Undigested Quinoa In Stool

VSMP (virtual symmetric multiprocessing)

thing I have been asking lately is when to use VSMP.
Should we assign to a VM with a virtual processor?

should use it only when we know that it will take for the applications that takes inside the VM, not simply by thinking "the more vCPU have VM better. "Some people think that the more vCPU have a better VM, and this is not necessarily true, it can actually run worse than with a two vCPU.

The reason for this is that the scheduler hypervisor CPU cores must find the number available simultaneously vCPUs equal to the number that is assigned the VM . For example, a VM with four vCPUs will have four cores available time for each request made to the host CPU. If such four cores are not available at this time (because there is another VM using two, for example) the VM must wait until they are available.

Tips about this: How
  • vCPUs least bring the VMs better.
  • only assigned to a VM multiple vCPUs when we know the application that is inside will make use of it.
  • never assign the same number of vCPUs that the total number of cores in your host. (PCPUs). Best if you keep me physical cores twice that of the VM vCPUs else has. (Eg, 8 physical cores = 4 vCPU maximum)
  • If you are doing P2V of a Windows server with multiple CPUs to a VM with a vCPU change the HAL from multiprocessor to uniprocessor.
  • If you can, avoid using CPU affinity.


Updated:
This link, although a bit old explains very technically the VSMP behavior and without it.

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