Re: [RFC] virtio_net: Adding tx_timeout function.

From: Michael S. Tsirkin
Date: Thu Jul 02 2015 - 06:00:46 EST

On Thu, Jul 02, 2015 at 03:23:56AM -0400, Pankaj Gupta wrote:
>
> > 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@xxxxxxxxxx>:
> > > >
> > > > 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@xxxxxxxxx>
> > > > > Cc: Jason Wang <jasowang@xxxxxxxxxx>
> > > >
> > > > 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.
>
> I am trying to understand how TX interrupt patches will help
> here? This function will be called when driver fails to send
> packets. Even before TX interrupt patches, packets are flowing.
>
> Is my understanding wrong some where?

Without tx interrupts, skbs are never freed until you send
more packets. Which might never happen.


> >
> >
> > > > > ---
> > > > > 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
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