From mboxrd@z Thu Jan  1 00:00:00 1970
From: Yuanhan Liu <yliu@fridaylinux.org>
Subject: Re: [PATCH 2/2] net/virtio: support GUEST ANNOUNCE
Date: Mon, 27 Nov 2017 20:48:55 +0800
Message-ID: <20171127124855.GB23415@yliu-home>
References: <1511521440-57724-1-git-send-email-xiao.w.wang@intel.com>
 <1511521440-57724-3-git-send-email-xiao.w.wang@intel.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Cc: dev@dpdk.org
To: Xiao Wang <xiao.w.wang@intel.com>
Return-path: <dev-bounces@dpdk.org>
Received: from out4-smtp.messagingengine.com (out4-smtp.messagingengine.com
 [66.111.4.28]) by dpdk.org (Postfix) with ESMTP id 1E4471B1B6
 for <dev@dpdk.org>; Mon, 27 Nov 2017 13:49:12 +0100 (CET)
Content-Disposition: inline
In-Reply-To: <1511521440-57724-3-git-send-email-xiao.w.wang@intel.com>
List-Id: DPDK patches and discussions <dev.dpdk.org>
List-Unsubscribe: <http://dpdk.org/ml/options/dev>,
 <mailto:dev-request@dpdk.org?subject=unsubscribe>
List-Archive: <http://dpdk.org/ml/archives/dev/>
List-Post: <mailto:dev@dpdk.org>
List-Help: <mailto:dev-request@dpdk.org?subject=help>
List-Subscribe: <http://dpdk.org/ml/listinfo/dev>,
 <mailto:dev-request@dpdk.org?subject=subscribe>
Errors-To: dev-bounces@dpdk.org
Sender: "dev" <dev-bounces@dpdk.org>

On Fri, Nov 24, 2017 at 03:04:00AM -0800, Xiao Wang wrote:
> When live migration is done, for the backup VM, either the virtio
> frontend or the vhost backend needs to send out gratuitous RARP packet
> to announce its new network location.
> 
> This patch enables VIRTIO_NET_F_GUEST_ANNOUNCE feature to support live
> migration scenario where the vhost backend doesn't have the ability to
> generate RARP packet.

Yes, it's a feature good to have.

> +static int
> +virtio_dev_pause(struct rte_eth_dev *dev)
> +{
> +	struct virtio_hw *hw = dev->data->dev_private;
> +
> +	if (hw->started == 0)
> +		return -1;
> +	hw->started = 0;
> +	/*
> +	 * Prevent the worker thread from touching queues to avoid condition,
> +	 * 1 ms should be enough for the ongoing Tx function to finish.
> +	 */
> +	rte_delay_ms(1);
> +	return 0;
> +}
> +
> +static void
> +virtio_dev_resume(struct rte_eth_dev *dev)
> +{
> +	struct virtio_hw *hw = dev->data->dev_private;
> +
> +	hw->started = 1;
> +}

However, the implementation (stop first, pause for 1ms, duplicate another
Tx function, resume) doesn't seem elegant.

You probably could try something like DPDK vhost does:

- set a flag when S_ANNOUCE is received
- inject a pkt when such flag is set in the xmit function

You then should be able to get rid of all of above stuffs.

	--yliu