Performance counter virtualization

[kayceesrk]

Currently performance counter MSRs are not advertised to the guest. Is this expected to change in the near future?

[xez]

Do you have a specific use case in mind? Performance counters are perturbed by host activity. Having them only count guest activity is a bit tricky and might require support from Hypervisor.framework. Even with support, the measurements might not end up being useful.

[kayceesrk]

The use case I have in mind is rr record and replay framework, which depends on certain performance counter features. However, it is unclear to me what subset of features are required for rr for its record and replay.

[sidkshatriya]

@xez and others:

This is actually quite a cool (and to my mind, important) feature. VMWare supports performance counter virtualization (also called PMU virtualization). Parallels also claims to do the same (though it seems to be broken).

Having this will allow some real powerful programs like mozilla/rr to be run on xhyve

Are there plans to support this now or in the future?

[rickard-von-essen]

@sidkshatriya Just a note about Parallels and the bug you link. The author uses a ~4 y old version of Parallels Desktop for Mac so I wouldn't assume that it the current state of PD PMU virtualization.

[sidkshatriya]

@rickard-von-essen Very useful observation -- Thanks for noticing that. Maybe you could update the ticket rr-debugger/rr#1818 with the same info?