Re: [RFC] virtio_net: Adding tx_timeout function.

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Jun 24, 2015 at 10:31:09PM -0300, Julio Faracco wrote:
> 2015-06-24 3:10 GMT-03:00 Michael S. Tsirkin <mst@redhat.com>:
> >
> > On Tue, Jun 23, 2015 at 10:44:29PM -0300, Julio Faracco wrote:
> > > virtio_net paravirtualized driver does not have a tx_timeout() function to
> > > guarantee that the driver will recover properly after receiving a timeout
> > > during a transmission of a packet. This patch add this feature and throw a
> > > timeout exception after 5 HZ. Considering some tests, this is the best
> > > time to use here.
> > >
> > > Signed-off-by: Julio Faracco <jcfaracco@gmail.com>
> > > Cc: Jason Wang <jasowang@redhat.com>
> >
> > Looks like a bunch of locks and flushes are missing in this patch.  IMHO
> > that's just too painful with current hardware.  IMO the right thing to
> > do here is to add ability to reset specific queues to hardware.
> >
> 
> I agree, Michael. This model is the default one resetting the device
> due to transmission timeout.
> To have a better performance, only some queues must be reset.

It's not a question of performance. You would need to write
a bunch of code anyway. Why not do it in the hypervisor
so guest can simply write into a register and reset
a ring?


BTW now that I think about it, this requires Jason's 
patches that introduce the tx interrupt, otherwise
packet will timeout simply because no packets are sent.


> > > ---
> > >  drivers/net/virtio_net.c |   69 +++++++++++++++++++++++++++++++++++++++++++++-
> > >  1 file changed, 68 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > > index 63c7810..75ac45c 100644
> > > --- a/drivers/net/virtio_net.c
> > > +++ b/drivers/net/virtio_net.c
> > > @@ -135,6 +135,9 @@ struct virtnet_info {
> > >       /* Work struct for config space updates */
> > >       struct work_struct config_work;
> > >
> > > +     /* Work struct for resetting the virtio-net driver. */
> > > +     struct work_struct reset_task;
> > > +
> > >       /* Does the affinity hint is set for virtqueues? */
> > >       bool affinity_hint_set;
> > >
> > > @@ -1394,6 +1397,18 @@ static int virtnet_change_mtu(struct net_device *dev, int new_mtu)
> > >       return 0;
> > >  }
> > >
> > > +static void virtnet_tx_timeout(struct net_device *dev)
> > > +{
> > > +     struct virtnet_info *vi = netdev_priv(dev);
> > > +
> > > +     dev_warn(&dev->dev, "TX Timeout exception with latency: %ld\n",
> > > +              jiffies - dev_trans_start(dev));
> > > +
> > > +     schedule_work(&vi->reset_task);
> >
> > What if after this triggers user does something
> > to the device (e.g. attempts to remove it)?
> > Or if a packet is transmitted or used?
> 
> At some point, this work must be canceled.
> Yes, you are right. Specially, when the driver is being removed.
> >
> > > +}
> > > +
> > > +static void virtnet_reset_task(struct work_struct *work);
> > > +
> > >  static const struct net_device_ops virtnet_netdev = {
> > >       .ndo_open            = virtnet_open,
> > >       .ndo_stop            = virtnet_close,
> > > @@ -1405,6 +1420,7 @@ static const struct net_device_ops virtnet_netdev = {
> > >       .ndo_get_stats64     = virtnet_stats,
> > >       .ndo_vlan_rx_add_vid = virtnet_vlan_rx_add_vid,
> > >       .ndo_vlan_rx_kill_vid = virtnet_vlan_rx_kill_vid,
> > > +     .ndo_tx_timeout      = virtnet_tx_timeout,
> > >  #ifdef CONFIG_NET_POLL_CONTROLLER
> > >       .ndo_poll_controller = virtnet_netpoll,
> > >  #endif
> > > @@ -1750,6 +1766,7 @@ static int virtnet_probe(struct virtio_device *vdev)
> > >       dev->netdev_ops = &virtnet_netdev;
> > >       dev->features = NETIF_F_HIGHDMA;
> > >
> > > +     dev->watchdog_timeo = 5 * HZ;
> > >       dev->ethtool_ops = &virtnet_ethtool_ops;
> > >       SET_NETDEV_DEV(dev, &vdev->dev);
> > >
> > > @@ -1811,6 +1828,7 @@ static int virtnet_probe(struct virtio_device *vdev)
> > >       }
> > >
> > >       INIT_WORK(&vi->config_work, virtnet_config_changed_work);
> > > +     INIT_WORK(&vi->reset_task, virtnet_reset_task);
> > >
> > >       /* If we can receive ANY GSO packets, we must allocate large ones. */
> > >       if (virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_TSO4) ||
> > > @@ -1891,7 +1909,7 @@ static int virtnet_probe(struct virtio_device *vdev)
> > >               netif_carrier_on(dev);
> > >       }
> > >
> > > -     pr_debug("virtnet: registered device %s with %d RX and TX vq's\n",
> > > +     pr_debug("virtio_net: registered device %s with %d RX and TX vq's\n",
> > >                dev->name, max_queue_pairs);
> > >
> > >       return 0;
> > > @@ -2001,6 +2019,55 @@ static int virtnet_restore(struct virtio_device *vdev)
> > >  }
> > >  #endif
> > >
> > > +static void virtnet_reset_task(struct work_struct *work)
> > > +{
> > > +     struct virtnet_info *vi =
> > > +             container_of(work, struct virtnet_info, reset_task);
> > > +     struct net_device *dev = vi->dev;
> > > +     struct virtio_device *vdev = vi->vdev;
> > > +     int err, i;
> > > +
> > > +     flush_work(&vi->config_work);
> > > +
> > > +     netif_device_detach(vi->dev);
> > > +     cancel_delayed_work_sync(&vi->refill);
> > > +
> > > +     if (netif_running(vi->dev)) {
> > > +             for (i = 0; i < vi->max_queue_pairs; i++) {
> > > +                     napi_disable(&vi->rq[i].napi);
> > > +                     napi_hash_del(&vi->rq[i].napi);
> > > +                     netif_napi_del(&vi->rq[i].napi);
> > > +             }
> > > +     }
> > > +
> > > +     remove_vq_common(vi);
> > > +
> > > +     dev->stats.tx_errors++;
> > > +
> > > +     err = init_vqs(vi);
> > > +     if (err) {
> > > +             dev_warn(&dev->dev, "virtio_net: virtqueue initialization failed.\n");
> > > +             return;
> > > +     }
> > > +
> > > +     virtio_device_ready(vdev);
> > > +
> > > +     if (netif_running(vi->dev)) {
> > > +             for (i = 0; i < vi->curr_queue_pairs; i++)
> > > +                     if (!try_fill_recv(vi, &vi->rq[i], GFP_KERNEL))
> > > +                             schedule_delayed_work(&vi->refill, 0);
> > > +
> > > +             for (i = 0; i < vi->max_queue_pairs; i++)
> > > +                     virtnet_napi_enable(&vi->rq[i]);
> > > +     }
> > > +
> > > +     netif_device_attach(vi->dev);
> > > +
> > > +     rtnl_lock();
> > > +     virtnet_set_queues(vi, vi->curr_queue_pairs);
> > > +     rtnl_unlock();
> >
> > Won't this lose a bunch of state, like mac addresses,
> > multicast, rx mode, etc etc?
> 
> I will rebase this patch with the properly changes and locks.
> After, I will resend it.
> 
> Thanks for your opinion, Michael.
> >
> >
> > > +}
> > > +
> > >  static struct virtio_device_id id_table[] = {
> > >       { VIRTIO_ID_NET, VIRTIO_DEV_ANY_ID },
> > >       { 0 },
> > > --
> > > 1.7.10.4