KVM supports the ability to publish the amount of time that VCPUs were runnable, but not running due to other host threads running instead, to the guest. The guest scheduler may use that information when making decisions and the guest may expose it to its userspace (Linux publishes this information in /proc/stat). This feature is called "steal time" as it represents the amount of time stolen from a guest by scheduling out its VCPUs. To enable this feature KVM userspace must provide a memory region that will be used to publish the information to the guest. The memory region is typical migratable region. The GPA of the region is given to KVM through a VCPU device ioctl interface. This feature is only available for 64-bit hosts running 64-bit guests.
This series provides the QEMU support of this feature. It will be enabled by default for 5.1 machine types and later, but may be disabled with a new CPU property "kvm-steal-time". While testing migration it was observed that the amount of steal time as viewed by the guest was getting reset on each migration. Patch 3/5 of a pvtime fix series posted[*] for KVM should fix that. Migration testing: * virt-5.0 can migrate as usual, no kvm-steal-time enabled * virt-5.1 can migrate between hosts with steal-time enabled and disabled when both hosts support steal-time * virt-5.1 with steal-time disabled can migrate to a host that does not support steal-time * virt-5.1 with steal-time enabled will cleanly fail when migrating to a host that does not support steal-time [*] https://lists.cs.columbia.edu/pipermail/kvmarm/2020-July/041538.html Thanks, drew Andrew Jones (3): hw/arm/virt: Move post cpu realize check into its own function hw/arm/virt: Move kvm pmu setup to virt_cpu_post_init hw/arm/virt: Implement kvm-steal-time docs/system/arm/cpu-features.rst | 11 ++++ hw/arm/virt.c | 103 +++++++++++++++++++++---------- include/hw/arm/virt.h | 2 + target/arm/cpu.c | 10 +++ target/arm/cpu.h | 4 ++ target/arm/kvm.c | 20 ++++++ target/arm/kvm32.c | 5 ++ target/arm/kvm64.c | 70 +++++++++++++++++++-- target/arm/kvm_arm.h | 24 ++++++- target/arm/monitor.c | 2 +- tests/qtest/arm-cpu-features.c | 25 ++++++-- 11 files changed, 232 insertions(+), 44 deletions(-) -- 2.25.4
