On 24/09/2026 18:29, Colton Lewis wrote:
This series creates a new PMU scheme on ARM, a partitioned PMU that allows reserving a subset of counters for more direct guest access, significantly reducing overhead. More details, including performance benchmarks, can be read in the v1 cover letter linked below. There is no longer a kernel command line parameter (`arm_pmuv3.reserved_host_counters`); PMU partitioning is now completely controlled via the KVM API using `KVM_ARM_VCPU_PMU_V3_ENABLE_PARTITION` and `KVM_ARM_VCPU_PMU_V3_SET_NR_COUNTERS` vCPU device attributes. When
As far as I know there isn't a straightforward way to get the number of hw counters from userspace. You have to either parse dmesg or attempt to open incrementally more counters in a group until it fails.
This makes doing things like "use all counters for guest" or "reserve two for the host" difficult. Maybe it's time to add a file to the PMU that userspace can use query this.
