From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([2001:4830:134:3::10]:45057)
	by lists.gnu.org with esmtp (Exim 4.71) (envelope-from <pl@kamp.de>)
	id 1bHnjj-0001so-3j
	for qemu-devel@nongnu.org; Tue, 28 Jun 2016 03:47:12 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <pl@kamp.de>) id 1bHnjd-0002Xb-VY
	for qemu-devel@nongnu.org; Tue, 28 Jun 2016 03:47:10 -0400
Received: from mx-v6.kamp.de ([2a02:248:0:51::16]:46858 helo=mx01.kamp.de)
	by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from <pl@kamp.de>)
	id 1bHnjd-0002XB-Lr
	for qemu-devel@nongnu.org; Tue, 28 Jun 2016 03:47:05 -0400
References: <5770F58F.2080402@kamp.de>
	<20160627170938.04a7a13c.cornelia.huck@de.ibm.com>
	<20160628100152-mutt-send-email-mst@redhat.com>
	<20160628094245.0fefc484.cornelia.huck@de.ibm.com>
From: Peter Lieven <pl@kamp.de>
Message-ID: <57722B75.9090406@kamp.de>
Date: Tue, 28 Jun 2016 09:47:01 +0200
MIME-Version: 1.0
In-Reply-To: <20160628094245.0fefc484.cornelia.huck@de.ibm.com>
Content-Type: text/plain; charset=windows-1252; format=flowed
Content-Transfer-Encoding: 7bit
Subject: Re: [Qemu-devel] Regression: virtio-pci: convert to ioeventfd
 callbacks
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: Cornelia Huck <cornelia.huck@de.ibm.com>, "Michael S. Tsirkin" <mst@redhat.com>
Cc: "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>, famz@redhat.com, stefanha@redhat.com

Am 28.06.2016 um 09:42 schrieb Cornelia Huck:
> On Tue, 28 Jun 2016 10:03:21 +0300
> "Michael S. Tsirkin" <mst@redhat.com> wrote:
>
>> I notice cleanup is a bit weird:
>>
>>          virtio_queue_set_host_notifier_fd_handler(vq, false, false);
>>          k->ioeventfd_assign(proxy, notifier, n, assign);
>>          event_notifier_cleanup(notifier);
>>
>> I think virtio_queue_set_host_notifier_fd_handler should happen
>> after ioeventfd_assign for symmetry with init?
> Looking at the pre-rework code, ccw used the order now in common code,
> while pci and mmio used the order you suggest.
>
> "Switch the handler back, then unassign the transport's ioeventfd
> backing" made more sense to me (regardless of symmetry) - but we might
> lose a notification?
>
> Peter: Can you check whether your problem goes away if you switch the
> two lines around?
>

The problem goes away, but its horribly slow. Maybe the lost notifications
you were thinking off.

diff --git a/hw/virtio/virtio-bus.c b/hw/virtio/virtio-bus.c
index 1313760..7924a59 100644
--- a/hw/virtio/virtio-bus.c
+++ b/hw/virtio/virtio-bus.c
@@ -176,9 +176,9 @@ static int set_host_notifier_internal(DeviceState *proxy, VirtioBusState *bus,
              return r;
          }
      } else {
-        virtio_queue_set_host_notifier_fd_handler(vq, false, false);
          k->ioeventfd_assign(proxy, notifier, n, assign);
          event_notifier_cleanup(notifier);
+        virtio_queue_set_host_notifier_fd_handler(vq, false, false);
      }
      return r;
  }

Peter