[v2,0/3] arm64: perf: Add support for event counting threshold

Message

James Clark Oct. 10, 2023, 10:40 a.m. UTC

Changes since v1:

  * Fix build on aarch32 by disabling FEAT_PMUv3_TH and splitting event
    type mask between the platforms
  * Change armv8pmu_write_evtype() to take unsigned long instead of u64
    so it isn't unnecessarily wide on aarch32
  * Add UL suffix to aarch64 event type mask definition

----

FEAT_PMUv3_TH (Armv8.8) is a new feature that allows conditional
counting of PMU events depending on how much the event increments on
a single cycle. Two new config fields for perf_event_open have been
added, and a PMU cap file for reading the max_threshold. See the second
commit message and the docs in the last commit for more details.

The change has been validated on the Arm FVP model:

  # Zero values, works as expected (as before).
  $ perf stat -e dtlb_walk/threshold=0,threshold_control=0/ -- true

    5962      dtlb_walk/threshold=0,threshold_control=0/

  # Threshold >= 255 causes count to be 0 because dtlb_walk doesn't
  # increase by more than 1 per cycle.
  $ perf stat -e dtlb_walk/threshold=255,threshold_control=5/ -- true

    0      dtlb_walk/threshold=255,threshold_control=5/
  
  # Keeping comparison as >= but lowering the threshold to 1 makes the
  # count return.
  $ perf stat -e dtlb_walk/threshold=1,threshold_control=5/ -- true

    6329      dtlb_walk/threshold=1,threshold_control=5/


James Clark (3):
  arm: perf: Include threshold control fields valid in PMEVTYPER mask
  arm64: perf: Add support for event counting threshold
  Documentation: arm64: Document the PMU event counting threshold
    feature

 Documentation/arch/arm64/perf.rst  | 58 ++++++++++++++++++++++++++
 arch/arm/include/asm/arm_pmuv3.h   |  3 ++
 arch/arm64/include/asm/arm_pmuv3.h |  4 ++
 arch/arm64/kvm/pmu-emul.c          |  1 +
 arch/arm64/kvm/sys_regs.c          |  1 +
 drivers/perf/arm_pmuv3.c           | 67 +++++++++++++++++++++++++++++-
 include/linux/perf/arm_pmuv3.h     |  4 +-
 7 files changed, 136 insertions(+), 2 deletions(-)


base-commit: 94f6f0550c625fab1f373bb86a6669b45e9748b3