Re: [PATCH 0/2] net/virtio: support to turn on/off the traffic flow

[Yuanhan Liu <yuanhan.liu@linux.intel.com>]

On Mon, Apr 17, 2017 at 08:50:52AM +0000, Yang, Zhiyong wrote:
> Hi, yuanhan:
> 	Sorry for the delay reply due to my annual leave.
> 
> > -----Original Message-----
> > From: Yuanhan Liu [mailto:yuanhan.liu@linux.intel.com]
> > Sent: Thursday, April 6, 2017 12:00 PM
> > To: Yang, Zhiyong <zhiyong.yang@intel.com>
> > Cc: dev@dpdk.org; maxime.coquelin@redhat.com
> > Subject: Re: [PATCH 0/2] net/virtio: support to turn on/off the traffic flow
> > 
> > On Fri, Mar 31, 2017 at 07:40:17PM +0800, Zhiyong Yang wrote:
> > > Current dpdk code virtio_dev_stop only disables interrupt and marks
> > > link down, When it is invoked, tx/rx traffic flows still work. This is a strange
> > behavior.
> > > The patchset supports the switch of flow by calling virtio_dev_start/stop.
> > >
> > > The implementation refers to vhost pmd.
> > 
> > That's a difference story. Vhost pmd uses 2 vars to track the status, whereas you
> > are using only one here. So why not setting/clearing "started" at dev_start/stop,
> > respectively?
> > Then we can check "started" at Rx/Tx functions.
> 
> Yes, I use only one var since I think vhost pmd using two is too complex and it is unnecessary.

No, it's needed. For vhost-user pmd, we can only do Rx when both below
items are met:

- port is started
- new_device() is invoked, aka, the device is connected

For that reason, two vars is used to track it.

> I'm setting/clearing started at virtio_dev_start/stop,  update_queuing_status is added to avoid
> duplicate code.

It's not about duplicate code. While we could make the var per-device,
you make it per-queue. That's complex and unnecessary.

> I don't understand your question.
> 
> > 
> > BTW, why does it have to be atomic?
> > 
> 
> Consider again. It is not necessary to use atomic here. But It seems that it doesn't  have an negative effect.

Hmm... that's a good reason to keep it, just because it has no negative
effect? Talking about the negative effect, badly, it really has. The
atomic is more expensive.

	--yliu