Date: Mon, 25 Jun 2007 19:49:57 +0400
From: Oleg Nesterov <oleg@tv-sign.ru>
To: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>,
       Andrew Morton <akpm@linux-foundation.org>,
       Nigel Cunningham <nigel@nigel.suspend2.net>,
       Pavel Machek <pavel@ucw.cz>, Uli Luckas <u.luckas@road.de>,
       linux-kernel@vger.kernel.org
Subject: Re: synchronize_qrcu_timeout()
Message-ID: <20070625154957.GA197@tv-sign.ru>
References: <20070625104332.GA147@tv-sign.ru> <20070625145851.GB12976@linux.vnet.ibm.com> <20070625152011.GA160@tv-sign.ru>
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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.

	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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