From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([2001:4830:134:3::10]:57329)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <famz@redhat.com>) id 1ZtFEo-0005v1-ES
	for qemu-devel@nongnu.org; Mon, 02 Nov 2015 08:33:31 -0500
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <famz@redhat.com>) id 1ZtFEn-00052O-Jb
	for qemu-devel@nongnu.org; Mon, 02 Nov 2015 08:33:30 -0500
Date: Mon, 2 Nov 2015 21:33:19 +0800
From: Fam Zheng <famz@redhat.com>
Message-ID: <20151102133319.GA10611@ad.usersys.redhat.com>
References: <1446177989-6702-1-git-send-email-famz@redhat.com>
	<1446177989-6702-4-git-send-email-famz@redhat.com>
	<20151030100724.GG4227@stefanha-x1.localdomain>
	<20151102023254.GA9184@ad.usersys.redhat.com>
	<20151102131916.GD10139@stefanha-x1.localdomain>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20151102131916.GD10139@stefanha-x1.localdomain>
Subject: Re: [Qemu-devel] [Qemu-block] [PATCH v4 3/3] aio: Introduce
	aio-epoll.c
List-Id: <qemu-devel.nongnu.org>
List-Unsubscribe: <https://lists.nongnu.org/mailman/options/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.nongnu.org/archive/html/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <https://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: Stefan Hajnoczi <stefanha@gmail.com>
Cc: Kevin Wolf <kwolf@redhat.com>, pbonzini@redhat.com, qemu-block@nongnu.org, qemu-devel@nongnu.org, Stefan Hajnoczi <stefanha@redhat.com>

On Mon, 11/02 13:19, Stefan Hajnoczi wrote:
> On Mon, Nov 02, 2015 at 10:32:54AM +0800, Fam Zheng wrote:
> > On Fri, 10/30 10:07, Stefan Hajnoczi wrote:
> > > On Fri, Oct 30, 2015 at 12:06:29PM +0800, Fam Zheng wrote:
> > > > To comply with aio_{disable,enable}_external, we always use ppoll when
> > > > aio_external_disabled() is true.
> > > 
> > > All file descriptors are added to the epoll fd.  Does that mean epoll
> > > will report the same fds again after we come out of
> > > ppoll()/aio_external_disabled()?
> > > 
> > > The two constraints to think about:
> > > 1. Ideally there should be no duplicated events.
> > > 2. There absolutely cannot be any missed events.
> > > 
> > 
> > I'm not sure I understood your question. The file descriptors added to epollfd
> > are always in sync with ppoll, so there is no difference between calling
> > epoll_wait and ppoll. When we come out of aio_external_disabled(), the same set
> > of fds will be polled, but the events got by ppoll should already be handled.
> > 
> > What am I missing?
> 
> I'm asking about duplicated events.  The epoll fd monitors the same set
> of fds as ppoll().  When we come out of aio_external_disabled() will
> epoll fd see the old events that have already been handled by ppoll()?

No, we don't get duplicated events. epoll fd will only see unhandled (new)
events.

Fam