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    SubjectRe: [PATCH] raise tsc clocksource rating
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    Zachary Amsden escreveu:
    > On Tue, 2007-10-30 at 00:02 +0100, Ingo Molnar wrote:
    >> * Zachary Amsden <zach@vmware.com> wrote:
    >
    >>> Not every guest support paravirt, but for correctness, all guests
    >>> require TSC, which must be exposed all the way up to userspace, no
    >>> matter what the efficiency or accuracy may be.
    >> but if there's a perfect TSC available (there is such hardware) then the
    >> TSC _is_ the best clocksource. Paravirt now turns it off unconditionally
    >> in essence.
    >
    > No, if no paravirt clocksource is detected, nothing can override the
    > perfect TSC hardware clocksource rating of 400. And if a paravirt
    > clocksource is detected, it is always better than TSC.

    Why always? tsc is the best possible alternative the _platform_ can
    provide. So the paravirt clocksource will be at best, as good as tsc.
    And if it is the case: why bother with communication mechanisms of all
    kinds, calculations, etc, if we can just read the tsc?

    Noting again: If the tsc does not arrive accurate to the guest, it will
    fail the tsc clocksource tests. So it will be rated zero anyway



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