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

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Message-ID: <20240801023927-mutt-send-email-mst@kernel.org>
Date: Thu, 1 Aug 2024 02:39:45 -0400
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Heng Qi <hengqi@...ux.alibaba.com>
Cc: netdev@...r.kernel.org, Jason Wang <jasowang@...hat.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>,
	virtualization@...ts.linux.dev,
	EugenioPérez <eperezma@...hat.com>
Subject: Re: [PATCH net v2] virtio-net: unbreak vq resizing when coalescing
 is not negotiated

On Thu, Aug 01, 2024 at 02:07:43PM +0800, Heng Qi wrote:
> On Wed, 31 Jul 2024 08:46:42 -0400, "Michael S. Tsirkin" <mst@...hat.com> 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" <mst@...hat.com> 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 <hengqi@...ux.alibaba.com>
> > > > > Reviewed-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
> > > > > Acked-by: Eugenio Pé rez <eperezma@...hat.com>
> > > > > Acked-by: Jason Wang <jasowang@...hat.com>
> > > > > ---
> > > > > 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.

Let's make this a separate patch then, please.

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