[PATCH 0/3] KVM: x86/pmu: Add hardware Topdown metrics support

[Zide Chen]

The Top-Down Microarchitecture Analysis (TMA) method is a structured
approach for identifying performance bottlenecks in out-of-order
processors.

Currently, guests support the TMA method by collecting Topdown events
using GP counters, which may trigger multiplexing.  To free up scarce
GP counters, eliminate multiplexing-induced skew, and obtain coherent
Topdown metric ratios, it is desirable to expose fixed counter 3 and
the IA32_PERF_METRICS MSR to guests.

Several failed attempts have been made to virtualize this under the
legacy vPMU model: [1], [2], [3].  With the new mediated vPMU, enabling
TMA support in guests becomes much simpler.  It avoids invasive changes
to the perf core, eliminates CPU pinning and fixed-counter affinity
issues, and reduces the overhead of trapping and emulating MSR accesses.

[1] https://lore.kernel.org/kvm/20231031090613.2872700-1-dapeng1.mi@xxxxxxxxxxxxxxx/
[2] https://lore.kernel.org/all/20230927033124.1226509-1-dapeng1.mi@xxxxxxxxxxxxxxx/T/
[3] https://lwn.net/ml/linux-kernel/20221212125844.41157-1-likexu@xxxxxxxxxxx/

Tested on an SPR.  Without this series, only raw topdown.*_slots events
work in the guest, and metric events (e.g. cpu/topdown-bad-spec/) are
not available.

With this series, metric events are visible in the guest.  Run this
command on both host and guest:

$ perf stat --topdown --no-metric-only -- taskset -c 2 perf bench sched messaging

Host results:

# Running 'sched/messaging' benchmark:
# 20 sender and receiver processes per group
# 10 groups == 400 processes run

     Total time: 1.500 [sec]

 Performance counter stats for 'taskset -c 2 perf bench sched messaging':

     4,266,060,558      TOPDOWN.SLOTS:u              #     32.0 %  tma_frontend_bound
                                                     #      5.2 %  tma_bad_speculation
       588,397,905      topdown-retiring:u           #     13.8 %  tma_retiring
                                                     #     49.0 %  tma_backend_bound
     1,376,283,990      topdown-fe-bound:u
     2,096,827,304      topdown-be-bound:u
       217,425,841      topdown-bad-spec:u
         5,050,520      INT_MISC.UOP_DROPPING:u

       1.755503765 seconds time elapsed

       0.235965000 seconds user
       1.500508000 seconds sys

Guest results:

# Running 'sched/messaging' benchmark:
# 20 sender and receiver processes per group
# 10 groups == 400 processes run

     Total time: 1.558 [sec]

 Performance counter stats for 'taskset -c 2 perf bench sched messaging':

     5,148,818,712      TOPDOWN.SLOTS:u              #     34.0 %  tma_frontend_bound
                                                     #      4.6 %  tma_bad_speculation
       602,862,499      topdown-retiring:u           #     11.7 %  tma_retiring
                                                     #     49.7 %  tma_backend_bound
     1,759,698,259      topdown-fe-bound:u
     2,565,571,672      topdown-be-bound:u
       230,277,308      topdown-bad-spec:u
         4,966,279      INT_MISC.UOP_DROPPING:u

       1.783366587 seconds time elapsed

       0.313692000 seconds user
       1.446377000 seconds sys

Dapeng Mi (2):
  KVM: x86/pmu: Support Intel fixed counter 3 on mediated vPMU
  KVM: x86/pmu: Support PERF_METRICS MSR in mediated vPMU

Zide Chen (1):
  KVM: x86/pmu: Do not map fixed counters >= 3 to generic perf events

 arch/x86/include/asm/kvm_host.h   |  3 +-
 arch/x86/include/asm/msr-index.h  |  1 +
 arch/x86/include/asm/perf_event.h |  1 +
 arch/x86/kvm/pmu.c                |  4 +++
 arch/x86/kvm/vmx/pmu_intel.c      | 57 ++++++++++++++++++++++++-------
 arch/x86/kvm/vmx/pmu_intel.h      |  5 +++
 arch/x86/kvm/vmx/vmx.c            |  6 ++++
 arch/x86/kvm/x86.c                | 10 ++++--
 8 files changed, 71 insertions(+), 16 deletions(-)

-- 
2.53.0