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SubjectRe: [PATCH] a local-timer-free version of RCU
On Sat, Nov 06, 2010 at 03:42:19PM -0400, Mathieu Desnoyers wrote:
> * Mathieu Desnoyers (mathieu.desnoyers@efficios.com) wrote:
> > > > +/**
> > > > + * rcu_read_unlock - marks the end of an RCU read-side critical section.
> > > > + * Check if a RCU batch was started while we were in the critical
> > > > + * section. If so, call rcu_quiescent() join the rendezvous.
> > > > + *
> > > > + * See rcu_read_lock() for more information.
> > > > + */
> > > > +void __rcu_read_unlock(void)
> > > > +{
> > > > + struct rcu_data *r;
> > > > + int cpu, flags;
> > > > +
> >
> > Another memory barrier would be needed here to ensure that the memory accesses
> > performed within the C.S. are not reordered wrt nest_count decrement.
>
> Nevermind. xchg() acts as a memory barrier, and nest_count is only ever touched
> by the local CPU. No memory barrier needed here.

You beat me to it. ;-)

Thanx, Paul

> Thanks,
>
> Mathieu
>
> >
> > > > + cpu = smp_processor_id();
> > > > + r = &per_cpu(rcu_data, cpu);
> > > > + if (--r->nest_count == 0) {
> > > > + flags = xchg(&r->flags, 0);
> > > > + if (flags & DO_RCU_COMPLETION)
> > > > + rcu_quiescent(cpu);
> > > > + }
> > > > +}
> > > > +EXPORT_SYMBOL(__rcu_read_unlock);
> >
> > Thanks,
> >
> > Mathieu
> >
> > --
> > Mathieu Desnoyers
> > Operating System Efficiency R&D Consultant
> > EfficiOS Inc.
> > http://www.efficios.com
>
> --
> Mathieu Desnoyers
> Operating System Efficiency R&D Consultant
> EfficiOS Inc.
> http://www.efficios.com
> --
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