Subject: Re: [PATCH net v2] virtio-net: unbreak vq resizing when coalescing is not negotiated

From: Heng Qi <[email-masked]>
Date: Thu, 1 Aug 2024 14:07:43 +0800

On Wed, 31 Jul 2024 08:46:42 -0400, "Michael S. Tsirkin" <[email-masked]> wrote:
> On Wed, Jul 31, 2024 at 08:25:23PM +0800, Heng Qi wrote:
> > On Wed, 31 Jul 2024 08:14:43 -0400, "Michael S. Tsirkin" <[email-masked]> wrote:
> > > On Wed, Jul 31, 2024 at 08:07:17PM +0800, Heng Qi wrote:
> > > > >From the virtio spec:
> > > > 
> > > > 	The driver MUST have negotiated the VIRTIO_NET_F_VQ_NOTF_COAL
> > > > 	feature when issuing commands VIRTIO_NET_CTRL_NOTF_COAL_VQ_SET
> > > > 	and VIRTIO_NET_CTRL_NOTF_COAL_VQ_GET.
> > > > 
> > > > The driver must not send vq notification coalescing commands if
> > > > VIRTIO_NET_F_VQ_NOTF_COAL is not negotiated. This limitation of course
> > > > applies to vq resize.
> > > > 
> > > > Fixes: f61fe5f081cf ("virtio-net: fix the vq coalescing setting for vq resize")
> > > > Signed-off-by: Heng Qi <[email-masked]>
> > > > Reviewed-by: Xuan Zhuo <[email-masked]>
> > > > Acked-by: Eugenio Pé rez <[email-masked]>
> > > > Acked-by: Jason Wang <[email-masked]>
> > > > ---
> > > > v1->v2:
> > > >  - Rephrase the subject.
> > > >  - Put the feature check inside the virtnet_send_{r,t}x_ctrl_coal_vq_cmd().
> > > > 
> > > >  drivers/net/virtio_net.c | 10 ++++++++--
> > > >  1 file changed, 8 insertions(+), 2 deletions(-)
> > > > 
> > > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > > > index 0383a3e136d6..2b566d893ea3 100644
> > > > --- a/drivers/net/virtio_net.c
> > > > +++ b/drivers/net/virtio_net.c
> > > > @@ -3658,6 +3658,9 @@ static int virtnet_send_rx_ctrl_coal_vq_cmd(struct virtnet_info *vi,
> > > >  {
> > > >  	int err;
> > > >  
> > > > +	if (!virtio_has_feature(vi->vdev, VIRTIO_NET_F_VQ_NOTF_COAL))
> > > > +		return -EOPNOTSUPP;
> > > > +
> > > >  	err = virtnet_send_ctrl_coal_vq_cmd(vi, rxq2vq(queue),
> > > >  					    max_usecs, max_packets);
> > > >  	if (err)
> > > > @@ -3675,6 +3678,9 @@ static int virtnet_send_tx_ctrl_coal_vq_cmd(struct virtnet_info *vi,
> > > >  {
> > > >  	int err;
> > > >  
> > > > +	if (!virtio_has_feature(vi->vdev, VIRTIO_NET_F_VQ_NOTF_COAL))
> > > > +		return -EOPNOTSUPP;
> > > > +
> > > >  	err = virtnet_send_ctrl_coal_vq_cmd(vi, txq2vq(queue),
> > > >  					    max_usecs, max_packets);
> > > >  	if (err)
> > > > @@ -3743,7 +3749,7 @@ static int virtnet_set_ringparam(struct net_device *dev,
> > > >  			err = virtnet_send_tx_ctrl_coal_vq_cmd(vi, i,
> > > >  							       vi->intr_coal_tx.max_usecs,
> > > >  							       vi->intr_coal_tx.max_packets);
> > > > -			if (err)
> > > > +			if (err && err != -EOPNOTSUPP)
> > > >  				return err;
> > > >  		}
> > > >
> > > 
> > > 
> > > So far so good.
> > >   
> > > > @@ -3758,7 +3764,7 @@ static int virtnet_set_ringparam(struct net_device *dev,
> > > >  							       vi->intr_coal_rx.max_usecs,
> > > >  							       vi->intr_coal_rx.max_packets);
> > > >  			mutex_unlock(&vi->rq[i].dim_lock);
> > > > -			if (err)
> > > > +			if (err && err != -EOPNOTSUPP)
> > > >  				return err;
> > > >  		}
> > > >  	}
> > > 
> > > I don't get this one. If resize is not supported,
> > 
> > Here means that the *dim feature* is not supported, not the *resize* feature.
> > 
> > > we pretend it was successful? Why?
> > 
> > During a resize, if the dim feature is not supported, the driver does not
> > need to try to recover any coalescing values, since the device does not have
> > these parameters.
> > Therefore, the resize should continue without interruption.
> > 
> > Thanks.
> 
> 
> you mean it's a separate bugfix?

Right.

Don't break resize when coalescing is not negotiated.

Thanks.

> > > > -- 
> > > > 2.32.0.3.g01195cf9f