Re: [PATCH] net/virtio: fix an incorrect behavior of device stop/start

[Yuanhan Liu <yliu@fridaylinux.org>]

On Fri, Sep 01, 2017 at 03:14:26PM +0800, Tiwei Bie wrote:
> > > > On Tue, Aug 29, 2017 at 04:26:01PM +0800, Tiwei Bie wrote:
> > > > > After starting a device, the driver shouldn't deliver the
> > > > > packets that already existed in the device before it is
> > > > > started to the applications.

Otherwise? I'm assuming you fixed a real issue? If so, it'd be better
if you can add a bit info about the issue.

> This patch fixes this issue
> > > > > by flushing the Rx queues when starting the device.
> > > > >
> > > > > Fixes: a85786dc816f ("virtio: fix states handling during initialization")
...
> > > > > @@ -1737,6 +1737,12 @@ virtio_dev_start(struct rte_eth_dev *dev)
> > > > > 		}
> > > > > 	}
> > > > >
> > > > > +	/* Flush the packets in Rx queues. */
> > > > > +	for (i = 0; i < dev->data->nb_rx_queues; i++) {
> > > > > +		rxvq = dev->data->rx_queues[i];
> > > > > +		virtqueue_flush(rxvq->vq);
> > > > > +	}
> > > > > +
> > > > 
> > > > A little bit further down is a for loop going over rx queues calling
> > > > notify. Could we flush directly before the notify and save the
> > > > additional loop?
> > > > 
> > > 
> > > I saw there is also another `for' loop to dump the Rx queues.
> > > And I think it makes the code more readable to flush the Rx
> > > queues in a separate `for' loop too. Besides, this function
> > > isn't performance critical. So I didn't combine them into one
> > > `for' loop.
> > 
> > To me code is better readable when it is concise, so I'd still vote for
> > combining the loops if its logically equivalent.
> > 
> > On the other hand I think this should be fixed soon, so
> > 
> > Reviewed-by: Jens Freimann <jfreimann@redhat.com>
> > 
> 
> Thank you! :-)
> 
> It's not a big deal. I'd like to leave it up to the maintainers.
> They can make the decision when applying the patch.

I agree with Jens here. We already have too many for loops in this
function. Let's not add yet another one. Besides that, the VIRTQUEU_DUMP
loop probably should also be removed and more it to the notify loop.

	--yliu