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    SubjectRe: [PATCH] KVM: VMX: CPU frequency scaling for intel x86_64 KVM guests
    On Tue, May 31, 2022 at 10:59:25AM +0000, Jack Allister wrote:
    > A VMM can control a vCPU's CPU frequency by interfacing with KVM via
    > the vCPU file descriptor to enable/set CPU frequency scaling for a
    > guest. Instead of creating a separate IOCTL to this this, KVM capabil-
    > ities are extended to include a capability called
    > KVM_CAP_CPU_FREQ_SCALING.
    >
    > A generic set_cpu_freq interface is added to kvm_x86_ops
    > to allow for architecture (AMD/Intel) independent CPU frequency
    > scaling setting.
    >
    > For Intel platforms, Hardware-Controlled Performance States (HWP) are
    > used to implement CPU scaling within the guest. Further information on
    > this mechanism can be seen in Intel SDM Vol 3B (section 14.4). The CPU
    > frequency is set as soon as this function is called and is kept running
    > until explicitly reset or set again.
    >
    > Currently the AMD frequency setting interface is left unimplemented.
    >
    > Please note that CPU frequency scaling will have an effect on host
    > processing in it's current form. To change back to full performance
    > when running in host context an IOCTL with a frequency value of 0
    > is needed to run back at uncapped speed.

    Nowhere does this explain *WHY* we would want to do this?

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