Re: [PATCH 2/2] net/virtio: support GUEST ANNOUNCE

[Yuanhan Liu <yliu@fridaylinux.org>]

On Thu, Nov 30, 2017 at 02:41:12AM +0000, Wang, Xiao W wrote:
> 
> 
> > -----Original Message-----
> > From: Yuanhan Liu [mailto:yliu@fridaylinux.org]
> > Sent: Monday, November 27, 2017 8:49 PM
> > To: Wang, Xiao W <xiao.w.wang@intel.com>
> > Cc: dev@dpdk.org
> > Subject: Re: [PATCH 2/2] net/virtio: support GUEST ANNOUNCE
> > 
> > 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
> 
> The difference is that the virtio port may just receive packet, without xmit.

Thanks, I missed that.

However, you really should not add a duplicate function. It adds more
maintain effort. I think you probably could just invoke the tx_pkt_burst
callback directly. You have stopped the device after all. What's the
necessary to duplicate it?

	--yliu