ARMv8 provides support for chained PMU counters, where an event type
of 0x001E is set for odd-numbered counters, the event counter will
increment by one for each overflow of the preceding even-numbered
counter. Let's emulate this in KVM by creating a 64 bit perf counter
when a user chains two emulated counters together.
Testing has been performed by hard-coding hwc->sample_period in
__hw_perf_event_init (arm_pmu.c) to a small value, this results in
regular overflows (for non sampling events). The following command
was then used to measure chained and non-chained instruction cycles:
perf stat -e armv8_pmuv3/long=1,inst_retired/u \
-e armv8_pmuv3/long=0,inst_retired/u dd if=/dev/zero bs=1M \
count=10 | gzip > /dev/null
The reported values were identical (and for non-chained was in the
same ballpark when running on a kernel without this patchset). Debug
was added to verify that the guest received overflow interrupts for
the chain counter.
Changes since v2:
- Rebased onto v5.0-rc7
- Add check for cycle counter in correct patch
- Minor style, naming and comment changes
- Extract armv8pmu_evtype_is_chain from arch/arm64/kernel/perf_event.c
into a common header that KVM can use
Changes since v1:
- Rename kvm_pmu_{enable,disable}_counter to reflect that they can
operate on multiple counters at once and use these functions where
possible
- Fix bugs with overflow handing, kvm_pmu_get_counter_value did not
take into consideration the perf counter value overflowing the low
counter
- Ensure PMCCFILTR_EL0 is used when operating on the cycle counter
- Rename kvm_pmu_reenable_enabled_{pair, single} and similar
- Always create perf event disabled to simplify logic elsewhere
- Move PMCNTENSET_EL0 test to kvm_pmu_enable_counter_mask
Andrew Murray (6):
KVM: arm/arm64: rename kvm_pmu_{enable/disable}_counter functions
KVM: arm/arm64: extract duplicated code to own function
KVM: arm/arm64: re-create event when setting counter value
KVM: arm/arm64: lazily create perf events on enable
arm64: perf: extract chain helper into header
KVM: arm/arm64: support chained PMU counters
arch/arm64/include/asm/perf_event.h | 5 +
arch/arm64/kernel/perf_event.c | 2 +-
arch/arm64/kvm/sys_regs.c | 4 +-
include/kvm/arm_pmu.h | 9 +-
virt/kvm/arm/pmu.c | 410 ++++++++++++++++++++++++++++++------
5 files changed, 360 insertions(+), 70 deletions(-)
--
2.7.4
