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    SubjectRe: [PATCH 1/2] KVM: LAPIC: Optimize timer latency consider world switch time
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    On 30/05/19 21:36, Sean Christopherson wrote:
    >> +u32 __read_mostly vmentry_lapic_timer_advance_ns = 0;
    >> +module_param(vmentry_lapic_timer_advance_ns, uint, S_IRUGO | S_IWUSR);
    > Hmm, an interesting idea would be to have some way to "lock" this param,
    > e.g. setting bit 0 locks the param. That would allow KVM to calculate the
    > cycles value to avoid the function call and the MUL+DIV. If I'm not
    > mistaken, vcpu->arch.virtual_tsc_khz is set only in kvm_set_tsc_khz().

    I would just make it read-only. But I'm afraid we're entering somewhat
    dangerous territory. There is a risk that the guest ends up entering
    the interrupt handler before the TSC deadline has actually expired, and
    there would be no way to know what would happen; even guest hangs are
    possible.

    Paolo

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