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    SubjectRe: kvm & dyntick

    * Avi Kivity <avi@qumranet.com> wrote:

    > >( for this to work on my system i have added a 'hyper' clocksource
    > > hypercall API for KVM guests to use - this is needed instead of the
    > > running-to-slowly TSC. )
    > >
    >
    > What's the problem with the TSC? The only issue I'm aware of is that
    > the tsc might go backwards if the vcpu is migrated to another host cpu
    > (easily fixed).

    this is not a problem of KVM - this is a problem of this laptop: its TSC
    stops when going idle. So the TSC is fundamentally unusable for reliable
    timekeeping - and qemu doesnt offer pmtimer emulation to fall back to,
    so the dyntick kernel refused to go high-res under KVM. Once i added the
    hyper clocksource to fall back to, it could utilize the PIT and the
    lapic for clock-events.

    Ingo
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