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    SubjectRe: question about RCU dynticks_nesting
    On Mon, May 04, 2015 at 12:39:23PM -0700, Paul E. McKenney wrote:
    > But in non-preemptible RCU, we have PREEMPT=n, so there is no preempt
    > counter in production kernels. Even if there was, we have to sample this
    > on other CPUs, so the overhead of preempt_disable() and preempt_enable()
    > would be where kernel entry/exit is, so I expect that this would be a
    > net loss in overall performance.

    We unconditionally have the preempt_count, its just not used much for
    PREEMPT_COUNT=n kernels.


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