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    SubjectRe: [tip:core/rcu] Revert "rcu: Decrease memory-barrier usage based on semi-formal proof"
    On 05/23/2011 06:18 PM, Paul E. McKenney wrote:

    > OK, so it looks like I need to get this out of the way in order to track
    > down the delays. Or does reverting PeterZ's patch get you a stable
    > system, but with the longish delays in memory_dev_init()? If the latter,
    > it might be more productive to handle the two problems separately.
    > For whatever it is worth, I do see about 5% increase in grace-period
    > duration when switching to kthreads. This is acceptable -- your
    > 30x increase clearly is completely unacceptable and must be fixed.
    > Other than that, the main thing that affects grace period duration is
    > the setting of CONFIG_HZ -- the smaller the HZ value, the longer the
    > grace-period duration.

    for my 1024g system when memory hotadd is enabled in kernel config:
    1. current linus tree + tip tree: memory_dev_init will take about 100s.
    2. current linus tree + tip tree + your tree - Peterz patch:
    a. on fedora 14 gcc: will cost about 4s: like old times
    b. on opensuse 11.3 gcc: will cost about 10s.


    Yinghai Lu

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