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    SubjectRe: [BUG] 2.6.37-rc3 massive interactivity regression on ARM
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    On Wed, 2010-12-08 at 14:28 +0000, Russell King - ARM Linux wrote:
    > So, what I'm saying is that if wrapping in 4 seconds is a problem,
    > then maybe we shouldn't be providing sched_clock() at all.

    4 seconds should be perfectly fine, we call it at least every scheduler
    tick (HZ) and NO_HZ will either have to limit the max sleep period or
    provide its own sleep duration (using a more expensive clock) so we can
    recover (much like GTOD already requires).

    > Also, if wrapping below 64-bits is also a problem, again, maybe we
    > shouldn't be providing it there either. Eg:

    That's mostly due to hysterical raisins and we should just fix that, the
    simplest way is to use something like kernel/sched_clock.c to use
    sched_clock() deltas to make a running u64 value.

    Like said, John Stultz was already looking at doing something like that
    because there's a number of architectures suffering this same problem
    and they're all already using part of the clocksource infrastructure to
    implement the sched_clock() interface simply because they only have a
    single hardware resource.

    One of the problems is I think the cycles2ns multiplication of the raw
    clock, that makes dealing with wrap-around lots harder, so I guess we
    should deal with the wrap on the raw clock values and then apply
    cycles2ns on the delta or somesuch. But I expect the clocksource
    infrastructure already has something like that, John?


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