netdev - Re: [PATCH V4 net-next 3/3] virtio-net: synchronize operstate with admin state on up/down

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Message-ID: <CACGkMEstXNPWqhxBXiU3_VnXgQrwHgJKPONRTisbG9mRMkosuA@mail.gmail.com>
Date: Thu, 1 Aug 2024 14:13:18 +0800
From: Jason Wang <jasowang@...hat.com>
To: "Michael S. Tsirkin" <mst@...hat.com>
Cc: xuanzhuo@...ux.alibaba.com, eperezma@...hat.com, davem@...emloft.net, 
	edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com, 
	virtualization@...ts.linux.dev, netdev@...r.kernel.org, 
	linux-kernel@...r.kernel.org, 
	Venkat Venkatsubra <venkat.x.venkatsubra@...cle.com>, 
	Gia-Khanh Nguyen <gia-khanh.nguyen@...cle.com>
Subject: Re: [PATCH V4 net-next 3/3] virtio-net: synchronize operstate with
 admin state on up/down

On Thu, Aug 1, 2024 at 1:58 PM Michael S. Tsirkin <mst@...hat.com> wrote:
>
> On Thu, Aug 01, 2024 at 10:16:00AM +0800, Jason Wang wrote:
> > > > @@ -2885,6 +2886,25 @@ static void virtnet_cancel_dim(struct virtnet_info *vi, struct dim *dim)
> > > >       net_dim_work_cancel(dim);
> > > >  }
> > > >
> > > > +static void virtnet_update_settings(struct virtnet_info *vi)
> > > > +{
> > > > +     u32 speed;
> > > > +     u8 duplex;
> > > > +
> > > > +     if (!virtio_has_feature(vi->vdev, VIRTIO_NET_F_SPEED_DUPLEX))
> > > > +             return;
> > > > +
> > > > +     virtio_cread_le(vi->vdev, struct virtio_net_config, speed, &speed);
> > > > +
> > > > +     if (ethtool_validate_speed(speed))
> > > > +             vi->speed = speed;
> > > > +
> > > > +     virtio_cread_le(vi->vdev, struct virtio_net_config, duplex, &duplex);
> > > > +
> > > > +     if (ethtool_validate_duplex(duplex))
> > > > +             vi->duplex = duplex;
> > > > +}
> > > > +
> > >
> > > I already commented on this approach.  This is now invoked on each open,
> > > lots of extra VM exits. No bueno, people are working hard to keep setup
> > > overhead under control. Handle this in the config change interrupt -
> > > your new infrastructure is perfect for this.
> >
> > No, in this version it doesn't. Config space read only happens if
> > there's a pending config interrupt during ndo_open:
> >
> > +       if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_STATUS)) {
> > +               if (vi->status & VIRTIO_NET_S_LINK_UP)
> > +                       netif_carrier_on(vi->dev);
> > +               virtio_config_driver_enable(vi->vdev);
> > +       } else {
> > +               vi->status = VIRTIO_NET_S_LINK_UP;
> > +               netif_carrier_on(dev);
> > +               virtnet_update_settings(vi);
> > +       }
>
> Sorry for being unclear, I was referring to !VIRTIO_NET_F_STATUS.
> I do not see why do we need to bother re-reading settings in this case at all,
> status is not there, nothing much changes.

Ok, let me remove it from the next version.

>
>
> > >
> > >
> > > >  static int virtnet_open(struct net_device *dev)
> > > >  {
> > > >       struct virtnet_info *vi = netdev_priv(dev);
> > > > @@ -2903,6 +2923,16 @@ static int virtnet_open(struct net_device *dev)
> > > >                       goto err_enable_qp;
> > > >       }
> > > >
> > > > +     if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_STATUS)) {
> > > > +             if (vi->status & VIRTIO_NET_S_LINK_UP)
> > > > +                     netif_carrier_on(vi->dev);
> > > > +             virtio_config_driver_enable(vi->vdev);
> > > > +     } else {
> > > > +             vi->status = VIRTIO_NET_S_LINK_UP;
> > > > +             netif_carrier_on(dev);
> > > > +             virtnet_update_settings(vi);
> > > > +     }
> > > > +
> > > >       return 0;
> > > >
> > > >  err_enable_qp:
> > > > @@ -3381,12 +3411,18 @@ static int virtnet_close(struct net_device *dev)
> > > >       disable_delayed_refill(vi);
> > > >       /* Make sure refill_work doesn't re-enable napi! */
> > > >       cancel_delayed_work_sync(&vi->refill);
> > > > +     /* Make sure config notification doesn't schedule config work */
> > >
> > > it's clear what this does even without a comment.
> > > what you should comment on, and do not, is *why*.
> >
> > Well, it just follows the existing style, for example the above said
> >
> > "/* Make sure refill_work doesn't re-enable napi! */"
>
> only at the grammar level.
> you don't see the difference?
>
>         /* Make sure refill_work doesn't re-enable napi! */
>         cancel_delayed_work_sync(&vi->refill);
>
> it explains why we cancel: to avoid re-enabling napi.
>
> why do you cancel config callback and work?
> comment should say that.

Something like "Prevent the config change callback from changing
carrier after close"?

>
>
>
> > >
> > > > +     virtio_config_driver_disable(vi->vdev);
> > > > +     /* Make sure status updating is cancelled */
> > >
> > > same
> > >
> > > also what "status updating"? confuses more than this clarifies.
> >
> > Does "Make sure the config changed work is cancelled" sounds better?
>
> no, this just repeats what code does.
> explain why you cancel it.

Does something like "Make sure carrier changes have been done by the
config change callback" works?

Thanks

>
>
>
> --
> MST
>