From mboxrd@z Thu Jan  1 00:00:00 1970
From: Olaf Hering <olaf@aepfle.de>
Subject: Re: Need help with fixing the Xen waitqueue feature
Date: Wed, 9 Nov 2011 08:02:17 +0100
Message-ID: <20111109070217.GA26154@aepfle.de>
References: <20111108214540.EAEBB72C4A1@homiemail-mx8.g.dreamhost.com>
	<c51adac89cc2096d54a7347c1accb18e.squirrel@webmail.lagarcavilla.org>
Mime-Version: 1.0
Content-Type: text/plain; charset=utf-8
Return-path: <xen-devel-bounces@lists.xensource.com>
Content-Disposition: inline
In-Reply-To: <c51adac89cc2096d54a7347c1accb18e.squirrel@webmail.lagarcavilla.org>
List-Unsubscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>,
	<mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe>
List-Post: <mailto:xen-devel@lists.xensource.com>
List-Help: <mailto:xen-devel-request@lists.xensource.com?subject=help>
List-Subscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>,
	<mailto:xen-devel-request@lists.xensource.com?subject=subscribe>
Sender: xen-devel-bounces@lists.xensource.com
Errors-To: xen-devel-bounces@lists.xensource.com
To: Andres Lagar-Cavilla <andres@lagarcavilla.org>
Cc: xen-devel@lists.xensource.com
List-Id: xen-devel@lists.xenproject.org

On Tue, Nov 08, Andres Lagar-Cavilla wrote:

> Olaf,
> are waitqueue's on the mem-event ring meant to be the way to deal with
> ring exhaustion? i.e. is this meant to go beyond a testing vehicle for
> waitqueue's?

Putting the guest to sleep when the ring is full is at least required
for p2m_mem_paging_drop_page(), so that the page gets informed about all
gfns from decrease_reservation.

> With the pager itself generating events, and foreign mappings generating
> events, you'll end up putting dom0 vcpu's in a waitqueue. This will
> basically deadlock the host.

Those vcpus can not go to sleep and my change handles that case.

Olaf