CPU usage on OpenVZ and KVM?

Question

OpenVZ

In PHP, the execution time of a resource-intensive script depends on the CPU load at a given time.
If I need to make accurate measurements of the script's running time, I take VDS, do not load it with anything, and run the script on a machine that is actually idle, measure the time.
The question is this: with OpenVZ virtualization (at the OS level), can the activity of other "neighbors" on the server affect the measurement time? Or do I just need to take KVM virtualization so that the results are reliable?

Answer 1

May affect. And on KVM it can. And on XEN it can. Any virtualization system, and even more so containers, can be easily oversold in terms of CPU, network, and disk. Those. sell more resources in total than a piece of iron with a hypervisor can directly give. Accordingly, several virtual machines will fight for resources and wait.
For a reliable benchmark, you need to take a dedicated piece of hardware or trust the hoster that it provides the CPU in the proper amount. For example, it assigns a separate physical core to the virtual machine and does not give it to anyone else.