FAQ - What are CPU Shares?
- 04/05/2012 12:27 AM
CPU shares determines the allocation of processing power allocated to a Virtual Machine in the Virtual Machine in the Cloud service.
The shares value represents the percentage of one CPU or "core" of the physical server. eApps Hosting uses dual quad core servers, meaning that the physical server has 8 CPU units. A technical feature of these servers, called hyperthreading, allows the physical server to appear to actually have 16 CPU units. Hyperthreading takes advantage of the fact that CPUs are often idle, waiting for other relatively slower processes such as disk drive accces, to complete.
So for the calculation of CPU power, assume that the physical server really has 16 CPUs. On this basis, CPU shares represents the allocation of those 16 CPUs. For example, a CPU share of 100 means that the virtual machine receives the equivalent of 100% of one CPU, or 1/16th of the total power of the physical machine. A CPU share of 200 represents 200% or two full CPUs, ie 1/8th of the power of the total physical server. A CPU share of 400 represents 100% of 4 (400%) CPUs, or 1/4 of the of the total power (1600) of the machine.