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    SubjectRe: [PATCH] simplify update_times (avoid jiffies/jiffies_64 aliasing problem)
    Andrew Morton writes:
    > Paul Mackerras <> wrote:
    > >
    > > Andi Kleen writes:
    > >
    > > > Also I assume Atsushi-san did the patch because he saw a real problem?
    > >
    > > Yes, one which I also saw on PPC. The compiler (gcc-4) emits loads
    > > for jiffies, jiffies64 and wall_jiffies before storing the incremented
    > > jiffies64 value back.
    > >
    > What was the effect of that?

    The effect is that the first call to do_timer doesn't increment xtime.
    This explains why the code I have to detect disagreements between
    xtime and the time of day as computed from the timebase register was
    finding a disagreement on the first tick, which I was scratching my
    head over.

    There may be other effects on architectures which use wall_jiffies to
    detect lost timer ticks. We don't have that problem on PPC and we
    don't use wall_jiffies in computing time of day.


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