On Mon, Jun 25, 2007 at 07:49:57PM +0400, Oleg Nesterov wrote:
> On 06/25, Oleg Nesterov wrote:
> >
> > On 06/25, Paul E. McKenney wrote:
> > >
> > > On Mon, Jun 25, 2007 at 02:43:32PM +0400, Oleg Nesterov wrote:
> > > >
> > > > Sadly, you can't use srcu/qrcu because it doesn't handle timeouts.
> > >
> > > Interesting... So the thought is to have a synchronize_srcu_timeout()
> > > or something similar that waited for a grace period to elapse or for
> > > a timeout to expire, whichever comes first? It should not be too hard
> > > to arrange something, if needed.
> >
> > Yes. As for qrcu (see http://marc.info/?t=116484476500001), I think it is easy.
> > First, we add "int interrupted" into struct qrcu_struct, then something like this
>
> Even simpler, we don't need ->interrupted.
I have to ask...
What sorts of performance characteristics are needed here? The reason
that I ask is because putting a straight synchronize_qrcu() into a
workqueue (or something similar) and then using a timer to provide
any needed wakeup seems a lot simpler than rearranging the innards of
synchronize_qrcu().
(Yes, I am feeling cowardly. Why do you ask?)
Thanx, Paul
> long synchronize_qrcu_timeout(struct qrcu_struct *qp, long tout)
> {
> int idx, prv;
>
> smp_mb();
> mutex_lock(&qp->mutex);
>
> idx = qp->completed & 0x1;
> prv = idx ^ 0x1;
>
> if (unlikely(atomic_read(qp->ctr + prv))) {
> // the previous call has not succeed,
> // finish the wait
> __wait_event_timeout(qp->wq, !atomic_read(qp->ctr + prv), tout);
> if (unlikely(!tout))
> goto out;
> }
>
> if (atomic_read(qp->ctr + idx) == 1)
> goto out;
>
> atomic_inc(qp->ctr + prv);
> qp->completed++;
>
> atomic_dec(qp->ctr + idx);
> __wait_event_timeout(qp->wq, !atomic_read(qp->ctr + idx), tout);
> out:
> mutex_unlock(&qp->mutex);
> smp_mb();
>
> return tout;
> }
>
> Oleg.
>
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