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    SubjectRe: [Xen-devel] [PATCH 05/12] xen/pvclock: add monotonicity check
    On 10/15/09 06:27, Dan Magenheimer wrote:
    > I understand but you are now essentially emulating a
    > reliable platform timer with a potentially unreliable
    > (but still high resolution) per-CPU timer AND probably
    > delivering that result to userland.
    > Read_tsc should only be used if either CONSTANT_TSC
    > or TSC_RELIABLE is true, so read_tsc is guaranteed
    > to be monotonically-strictly-increasing by hardware
    > (and enforced for CONSTANT_TSC by check_tsc_warp
    > at boot).

    read_tsc clearly isn't expected to produce absolutely globally monotonic
    results; if it were then the check wouldn't be necessary.


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