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
long synchronize_qrcu_timeout(struct qrcu_struct *qp, long tout)
{
int idx;
smp_mb();
mutex_lock(&qp->mutex);
again:
idx = qp->completed & 0x1;
if (unlikely(qp->interrupted)) {
idx ^= 0x1;
goto restart;
}
if (atomic_read(qp->ctr + idx) == 1)
goto out;
atomic_inc(qp->ctr + (idx ^ 0x1));
qp->completed++;
atomic_dec(qp->ctr + idx);
restart:
__wait_event_timeout(qp->wq, !atomic_read(qp->ctr + idx), tout);
if (unlikely(!tout)) {
qp->interrupted = 1;
goto out;
}
if (unlikely(qp->interrupted)) {
qp->interrupted = 0;
goto again;
}
out:
mutex_unlock(&qp->mutex);
smp_mb();
return tout;
}
Of course, this needs some other changes to implement synchronize_qrcu() on top
of synchronize_qrcu_timeout(). I also think that this doesn't break
[RFC PATCH] QRCU fastpath optimization
http://marc.info/?l=linux-kernel&m=117125577710947
Looks like we can do something similar for srcu.
Oleg.
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