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    SubjectRe: [PATCH 2/2] locking/percpu-rwsem: Introduce bias knob
    On Thu, Jul 14, 2016 at 08:25:47PM +0200, Peter Zijlstra wrote:
    > @@ -19,6 +20,13 @@ int __percpu_init_rwsem(struct percpu_rw
    >
    > /* ->rw_sem represents the whole percpu_rw_semaphore for lockdep */
    > rcu_sync_init(&sem->rss, RCU_SCHED_SYNC);
    > + if (bias == PERCPU_RWSEM_WRITER) {
    > + /*
    > + * Disable rcu_sync() and force slow path.
    > + */
    > + sem->rss.gp_count++;
    > + sem->rss.gp_state = !0;
    > + }
    > __init_rwsem(&sem->rw_sem, name, rwsem_key);
    > init_waitqueue_head(&sem->writer);
    > sem->state = readers_slow;

    So this seemed like a better deal than calling rcu_sync_enter(), because
    that would still incur a (pointless) synchronize_sched() at init time
    and people do tend to complain about things like that.

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