[v1,0/2] arm64: perf: Add support for event counting threshold

Message

James Clark Sept. 19, 2023, 9:51 a.m. UTC

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 first
commit message and the docs in the second 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 (2):
  arm64: perf: Add support for event counting threshold
  Documentation: arm64: Document the PMU event counting threshold
    feature

 Documentation/arch/arm64/perf.rst | 58 ++++++++++++++++++++++++++++++
 drivers/perf/arm_pmuv3.c          | 59 ++++++++++++++++++++++++++++++-
 include/linux/perf/arm_pmuv3.h    |  7 +++-
 3 files changed, 122 insertions(+), 2 deletions(-)


base-commit: 21b61fe48c2fc43d98ebb67a1f3832e0478fa523