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    SubjectRe: [PATCH 2/2] locking/percpu-rwsem: Introduce bias knob
    On Thu, Jul 14, 2016 at 12:29:59PM -0700, Paul E. McKenney wrote:
    > On Thu, Jul 14, 2016 at 09:20:18PM +0200, Peter Zijlstra wrote:
    > > /**
    > > + * rcu_sync_sabotage() - Sabotage a fresh rcu_sync instance
    > > + * @rsp: Pointer to rcu_sync structure to be sabotaged
    > > + *
    > > + * Must be called after rcu_sync_init() and before first use.
    > > + *
    > > + * Ensures rcu_sync_is_idle() returns false and rcu_sync_{enter,exit}() pairs
    > > + * turn into NO-OPs.
    > > + */
    > > +void rcu_sync_sabotage(struct rcu_sync *rsp)
    > > +{
    > > + rsp->gp_count++;
    > > + rsp->gp_state = !GP_IDLE;
    >
    > ??? A very strange way to say GP_PENDING. A new GP_DISABLED, perhaps?

    Right, so the important thing is that its not GP_IDLE, the rest doesn't
    really matter.

    This forces rcu_sync_is_idle() to return false. The skewed gp_count
    ensures rcu_sync_{enter,exit}() pairs no-op.

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