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
--
2.34.1
