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    SubjectRe: [PATCH 1/2] Dynamic Tick: Prevent clocksource wrapping during idle
    On Wed, 27 May 2009, Alok Kataria wrote:

    > On Wed, May 27, 2009 at 7:49 AM, Jon Hunter <jon-hunter@ti.com> wrote:
    > >
    > > The dynamic tick allows the kernel to sleep for periods longer than a single
    > > tick. This patch prevents that the kernel from sleeping for a period longer
    > > than the maximum time that the current clocksource can count. This ensures
    > > that the kernel will not lose track of time. This patch adds a new function
    > > called "timekeeping_max_deferment()" that calculates the maximum time the
    > > kernel can sleep for a given clocksource.
    > >
    >
    > >From the patch description I understand that this will avoid wrapping
    > around for only the *current* clocksource. What happens if, say, TSC
    > is the clocksource and ACPI_PM is being used as the
    > watchdog_clocksource, in that case the timekeeping_max_deferement will
    > give TSC' max allowed sleep value (which is greater than ACPI_PMs).
    > i.e. We could still sleep beyond ACPI_PM's wrap around threshold which
    > may result in us marking TSC as unsuable as a clocksource.
    > That could still result in incorrect timekeeping right ?

    No, because the watchdog timer takes care of that. It wakes up at time.

    Thanks,

    tglx


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