From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43)
	id 1Jfukx-0001bu-OF
	for qemu-devel@nongnu.org; Sun, 30 Mar 2008 06:27:19 -0400
Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43)
	id 1Jfuku-0001Yb-DR
	for qemu-devel@nongnu.org; Sun, 30 Mar 2008 06:27:18 -0400
Received: from [199.232.76.173] (helo=monty-python.gnu.org)
	by lists.gnu.org with esmtp (Exim 4.43) id 1Jfuku-0001YC-3o
	for qemu-devel@nongnu.org; Sun, 30 Mar 2008 06:27:16 -0400
Received: from mail.codesourcery.com ([65.74.133.4])
	by monty-python.gnu.org with esmtps
	(TLS-1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.60)
	(envelope-from <paul@codesourcery.com>) id 1Jfuks-0004Oi-Te
	for qemu-devel@nongnu.org; Sun, 30 Mar 2008 06:27:15 -0400
From: Paul Brook <paul@codesourcery.com>
Subject: Re: [Qemu-devel] [PATCH 4/6] virtio network driver
Date: Sun, 30 Mar 2008 10:27:07 +0000
References: <1206827760-4566-1-git-send-email-aliguori@us.ibm.com>
	<1206827760-4566-4-git-send-email-aliguori@us.ibm.com>
In-Reply-To: <1206827760-4566-4-git-send-email-aliguori@us.ibm.com>
MIME-Version: 1.0
Content-Type: text/plain;
  charset="iso-8859-1"
Content-Transfer-Encoding: quoted-printable
Content-Disposition: inline
Message-Id: <200803301127.08620.paul@codesourcery.com>
Reply-To: qemu-devel@nongnu.org
List-Id: qemu-devel.nongnu.org
List-Unsubscribe: <http://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.gnu.org/pipermail/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <http://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: qemu-devel@nongnu.org
Cc: kvm-devel@lists.sourceforge.net, Marcelo Tosatti <marcelo@kvack.org>, Anthony Liguori <aliguori@us.ibm.com>, Aurelien Jarno <aurelien@aurel32.net>

On Saturday 29 March 2008, Anthony Liguori wrote:
> + =A0 =A0if ((elem =3D virtqueue_pop(n->rx_vq)) =3D=3D NULL) {
> +=A0=A0=A0=A0=A0=A0=A0/* wait until the guest adds some rx bufs */
> +=A0=A0=A0=A0=A0=A0=A0n->can_receive =3D 0;
> +=A0=A0=A0=A0=A0=A0=A0return;
> + =A0 =A0}

Setting can_receive to zero *after* dropping a packet is a bit late.
Not a fatal flaw, but it does make can_receive fairly useless. The whole po=
int=20
of can_receive is to workaround lack of proper TCP rate control in the slir=
p=20
code.

Paul