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    SubjectRe: [PATCH] sched_clock: prevent scd->clock from moving backwards

    * Dave Kleikamp <shaggy@linux.vnet.ibm.com> wrote:

    > On Thu, 2008-10-09 at 12:54 -0500, Dave Kleikamp wrote:
    >
    > > I'll fix the patch and retest it before sending it again.
    >
    > I'm definitely running with the new patch now. Here goes:
    > -------------------------------------------------
    > sched_clock: prevent scd->clock from moving backwards
    >
    > When sched_clock_cpu() couples the clocks between two cpus, it may
    > increment scd->clock beyond the GTOD tick window that __update_sched_clock()
    > uses to clamp the clock. A later call to __update_sched_clock() may move
    > the clock back to scd->tick_gtod + TICK_NSEC, violating the clock's
    > monotonic property.
    >
    > This patch ensures that scd->clock will not be set backward.
    >
    > Signed-off-by: Dave Kleikamp <shaggy@linux.vnet.ibm.com>
    > Cc: Ingo Molnar <mingo@elte.hu>
    > Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>

    applied to tip/sched/clock, thanks Dave!

    Ingo


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