linux-kernel - Re: synchronize_qrcu

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

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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