What's the fixed cycle counter virtualization issue on AWS?

[peihongch]

When running pcm-core inside a virtual machine, I observed the following output:

...
INFO: Reducing the number of programmable counters to 3 to workaround the fixed cycle counter virtualization issue on AWS.
      You can disable the workaround by setting PCM_NO_AWS_WORKAROUND=1 environment variable
...

I would like to better understand this behavior.

Could someone explain what the “fixed cycle counter virtualization issue” refers to, especially in the context of AWS or virtualized environments?

Additionally, how does the PCM_NO_AWS_WORKAROUND=1 environment variable change the behavior of PCM, and in what scenarios is it safe or recommended to disable this workaround?

Thanks in advance for any clarification!