On Wed, Jan 18, 2023 at 3:21 PM Anthony Harivel <aharivel@xxxxxxxxxx> wrote:
>
> Allow userspace to update the MSR_RAPL_POWER_UNIT and
> MSR_PKG_POWER_STATUS powercap registers. By default, these MSRs still
> return 0.
>
> This enables VMMs running on top of KVM with access to energy metrics
> like /sys/devices/virtual/powercap/*/*/energy_uj to compute VMs power
> values in proportion with other metrics (e.g. CPU %guest, steal time,
> etc.) and periodically update the MSRs with ioctl KVM_SET_MSRS so that
> the guest OS can consume them using power metering tools.
Do you have a QEMU prototype patch? My gut feeling is that these MSRs
should be handled entirely within KVM using the sched_in and sched_out
notifiers. This would also allow exposing the values to the host using
the statistics subsystem.
Paolo
> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Cc: Christophe Fontaine <cfontain@xxxxxxxxxx>
> Signed-off-by: Anthony Harivel <aharivel@xxxxxxxxxx>
> ---
>
> Notes:
> The main goal of this patch is to bring a first step to give energy
> awareness to VMs.
>
> As of today, KVM always report 0 in these MSRs since the entire host
> power consumption needs to be hidden from the guests. However, there is
> no fallback mechanism for VMs to measure their power usage.
>
> The idea is to let the VMMs running on top of KVM periodically update
> those MSRs with representative values of the VM's power consumption.
>
> If this solution is accepted, VMMs like QEMU will need to be patched to
> set proper values in these registers and enable power metering in
> guests.
>
> I am submitting this as an RFC to get input/feedback from a broader
> audience who may be aware of potential side effects of such a mechanism.
>
> Regards,
> Anthony
>
> "If you can’t measure it, you can’t improve it." – Lord Kelvin
>
> arch/x86/include/asm/kvm_host.h | 4 ++++
> arch/x86/kvm/x86.c | 18 ++++++++++++++++--
> 2 files changed, 20 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 6aaae18f1854..c6072915f229 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1006,6 +1006,10 @@ struct kvm_vcpu_arch {
> */
> bool pdptrs_from_userspace;
>
> + /* Powercap related MSRs */
> + u64 msr_rapl_power_unit;
> + u64 msr_pkg_energy_status;
> +
> #if IS_ENABLED(CONFIG_HYPERV)
> hpa_t hv_root_tdp;
> #endif
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index da4bbd043a7b..adc89144f84f 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1528,6 +1528,10 @@ static const u32 emulated_msrs_all[] = {
>
> MSR_K7_HWCR,
> MSR_KVM_POLL_CONTROL,
> +
> + /* The following MSRs can be updated by the userspace */
> + MSR_RAPL_POWER_UNIT,
> + MSR_PKG_ENERGY_STATUS,
> };
>
> static u32 emulated_msrs[ARRAY_SIZE(emulated_msrs_all)];
> @@ -3888,6 +3892,12 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
> * as to-be-saved, even if an MSRs isn't fully supported.
> */
> return !msr_info->host_initiated || data;
> + case MSR_RAPL_POWER_UNIT:
> + vcpu->arch.msr_rapl_power_unit = data;
> + break;
> + case MSR_PKG_ENERGY_STATUS:
> + vcpu->arch.msr_pkg_energy_status = data;
> + break;
> default:
> if (kvm_pmu_is_valid_msr(vcpu, msr))
> return kvm_pmu_set_msr(vcpu, msr_info);
> @@ -3973,13 +3983,17 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
> * data here. Do not conditionalize this on CPUID, as KVM does not do
> * so for existing CPU-specific MSRs.
> */
> - case MSR_RAPL_POWER_UNIT:
> case MSR_PP0_ENERGY_STATUS: /* Power plane 0 (core) */
> case MSR_PP1_ENERGY_STATUS: /* Power plane 1 (graphics uncore) */
> - case MSR_PKG_ENERGY_STATUS: /* Total package */
> case MSR_DRAM_ENERGY_STATUS: /* DRAM controller */
> msr_info->data = 0;
> break;
> + case MSR_RAPL_POWER_UNIT:
> + msr_info->data = vcpu->arch.msr_rapl_power_unit;
> + break;
> + case MSR_PKG_ENERGY_STATUS: /* Total package */
> + msr_info->data = vcpu->arch.msr_pkg_energy_status;
> + break;
> case MSR_IA32_PEBS_ENABLE:
> case MSR_IA32_DS_AREA:
> case MSR_PEBS_DATA_CFG:
> --
> 2.39.0
>
