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    SubjectRe: [PATCH v2] rwsem: Support optimistic spinning
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    On Wed, 2014-04-30 at 11:21 +0200, Peter Zijlstra wrote:
    > On Mon, Apr 28, 2014 at 03:09:01PM -0700, Davidlohr Bueso wrote:
    > > +#ifdef CONFIG_SMP
    >
    > > +#else
    > > +static bool rwsem_optimistic_spin(struct rw_semaphore *sem)
    > > +{
    > > + return false;
    > > +}
    > > +#endif
    >
    > On the mutex side we guard this with MUTEX_SPIN_ON_OWNER, do we want to
    > use that here too?

    I thought of it, but hated adding mutex naming to rwsem code -- we
    already do it for cpu_relax() thanks to s390.

    MUTEX_SPIN_ON_OWNER depends on SMP && !DEBUG_MUTEXES.
    Right now rwsem optimistic spinning depends on SMP && RWSEM_XCHGADD_ALGORITHM.

    It might sense to add RWSEM_SPIN_ON_OWNER to encapsulate what we already
    have. I don't think we want DEBUG_MUTEX dependencies in rwsems. Would
    you accept such thing?

    Thanks,
    Davidlohr



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