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.
For chained events we only support generating an overflow interrupt
on the high counter. We use the attributes of the low counter to
determine the attributes of the perf event.
Changes since v3:
- Simplify approach by not creating events lazily and by introducing
a struct kvm_pmc_pair to represent the relationship between
adjacent counters.
- Rebase onto v5.1-rc2
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
arm64: perf: extract chain helper into header
KVM: arm/arm64: represent paired counters with kvm_pmc_pair
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 | 23 +-
virt/kvm/arm/pmu.c | 396 +++++++++++++++++++++++-----
5 files changed, 359 insertions(+), 71 deletions(-)
--
2.21.0
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