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    SubjectRe: Real-Time Preemption and RCU

    * Ingo Molnar <mingo@elte.hu> wrote:

    > there's one detail on PREEMPT_RT though (which i think you noticed too).
    >
    > Priority inheritance handling can be done in a pretty straightforward
    > way as long as no true read-side nesting is allowed for rwsems and
    > rwlocks - i.e. there's only one owner of a lock at a time. So
    > PREEMPT_RT restricts rwsem and rwlock concurrency: readers are
    > writers, with the only exception that they are allowed to 'self-nest'.
    > [...]

    this does not affect read-side RCU, because read-side RCU can never
    block a higher-prio thread. (as long as callback processing is pushed
    into a separate kernel thread.)

    so RCU will be pretty much the only mechanism (besides lock-free code)
    that allows reader concurrency on PREEMPT_RT.

    Ingo
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