RE: bpf_get_branch_snapshot on qemu-kvm

quoted

quoted

- get confirmation that clearing GLOBAL_CTRL is suffient to supress
  PEBS, in which case we can simply remove the PEBS_ENABLE clear.

How should we confirm this? Can we run some tests for this? Or do we
need hardware experts' input for this?

I'll put it on the list to ask the hardware people when I talk to them next. But
maybe Kan or Andi know without asking.

If the GLOBAL_CTRL is explicitly disabled, the counters do not count anymore.
It doesn't matter if PEBS is enabled or not. 

See 6c1c07b33eb0 ("perf/x86/intel: Avoid unnecessary PEBS_ENABLE MSR
access in PMI "). We optimized the PMU handler base on it.

Thanks,
Kan