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* Check whether perf_event does unnecessary RMW operations on MSRs, which are significantly slow in a guest
 
* 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
 
* Add a paravirt batch MSR read/write facility, update perf to use it when available
* Change perf to use an ordinary interrupt instead of NMI when profiling only user space (reduces work in NMI context)
+
* Change perf to use an ordinary interrupt instead of NMI when profiling only user space, or only a guest (reduces work in NMI context)
  
 
= Git repositories =
 
= Git repositories =

Revision as of 06:41, 6 September 2011

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
  • Change perf to use an ordinary interrupt instead of NMI when profiling only user space, or only a guest (reduces work in NMI context)

Git repositories

Guest PMU: git://github.com/avikivity/kvm.git pmu

exclude_host: git://github.com/avikivity/kvm.git perf-guest-counting