Guest PMU

Guest PMU (Performance Monitoring Unit) currently exists in the form of an out-of-tree patchset.

See the Forum 2011 presentation about the state as of August 2011.

Current status

Version 1 Architectural PMU on Intel and AMD hosts is implemented and works.

TODO

Guest visible features

• Implement Version 2 Architectural PMU - allows faster switch times using PERF_GLOBAL_ENABLE MSR
• Implement Version 3 Architectural PMU
• Model specific PMU - allows access to more events and support for more tools; but restricts live migration capabilities
  • Need per-event validation to avoid leaking socket-wide or core-wide information
• PEBS - Preceise Event Based Sampling - allows examining program state
• BTS - Branch Trace Store - allows tracing program execution accurately

Accuracy

• Update Joerg Roedel's exclude_guest/exclude_host patchset to support Intel hosts, using vmx's ability to load PERF_GLOBAL_ENABLE on vmentry/vmexit

Performance

• Investigate reports that enabling the guest PMU reduces performance
• Update the perf_event subsystem to make use of the PERF_GLOBAL_ENABLE MSR to speed up context switching, on both guest and host
• Check whether perf_event does unnecessary RMW operations on MSRs, which are significantly slow in a guest
• Add a paravirt batch MSR read/write facility, update perf to use it when available