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    SubjectRe: [RFC PATCH-tip v2 1/6] locking/osq: Make lock/unlock proper acquire/release barrier
    On Sat, Jun 18, 2016 at 04:46:20PM +0800, Boqun Feng wrote:
    > On Fri, Jun 17, 2016 at 02:17:27PM -0400, Waiman Long wrote:
    > > keep the xchg() function as it is or use smp_store_release(&next->locked,
    > > 1). So which one is a better alternative for ARM or PPC?
    > >
    >
    > For PPC, I think xchg_release() + smp_store_release() is better than the
    > current code, because the former has two lwsync while the latter has two
    > sync, and sync is quite expensive than lwsync on PPC.
    >
    > I need to leave the ARM part to Will ;-)

    I doubt there's much in it, but xchg() has DMB + release, so xchg_release +
    smp_store_release is probably slightly better for us too.

    Will

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