[PATCH v2 0/3] powerpc/perf: Fix vpa-pmu driver to report correct numbers

[Gautam Menghani]

The vpa-pmu driver can sometimes report incorrect context switch latency
numbers:

$ perf stat -e vpa_pmu/l1_to_l2_lat/  --tid=2061  -I 1000
           time             counts unit events
     1.001022517 18,446,744,073,708,177,408      vpa_pmu/l1_to_l2_lat/
     2.002120674            345,092      vpa_pmu/l1_to_l2_lat/
     3.003171582            406,342      vpa_pmu/l1_to_l2_lat/
     4.004234838            340,836      vpa_pmu/l1_to_l2_lat/

These invalid numbers are observed because the vpa-pmu driver does not
handle the following scenarios:

1. The vCPU process gets rescheduled to a different host cpu.

2. The vCPU process is not running, and vpa_pmu_read() is called to read
counter values.

Fix the above cases by maintaining aggregate counter values inside the
vcpu->arch struct and using them to report data.


changes in v2:
1. Fix the output for "perf stat --cpu ..."
2. Add stable and fixes tags

Gautam Menghani (3):
  KVM: PPC: Book3S HV: Maintain aggregate context switch values for
    vCPUs
  powerpc/perf: Use the aggregate context switch values from vcpu struct
  powerpc/perf: Update prev_count of event to get accurate values

 arch/powerpc/include/asm/kvm_book3s_64.h |  3 --
 arch/powerpc/kvm/book3s_hv.c             | 51 ++----------------------
 arch/powerpc/perf/vpa-pmu.c              | 25 +++++++++---
 3 files changed, 22 insertions(+), 57 deletions(-)

-- 
2.54.0