On Thu, 10 Jun 2010 10:17:07 -0700
Sridhar Samudrala <s...@us.ibm.com> wrote:
> On Thu, 2010-06-10 at 18:20 +0300, Michael S. Tsirkin wrote:
> > virtio net will never try to overflow the TX ring, so the only reason
> > add_buf may fail is out of memory. Thus, we can not stop the
> > device until some request completes - there's no guarantee anything
> > at all is outstanding.
> >
> > Make the error message clearer as well: error here does not
> > indicate queue full.
> >
> > Signed-off-by: Michael S. Tsirkin <m...@redhat.com>
> > ---
> > drivers/net/virtio_net.c | 15 ++++++++-------
> > 1 files changed, 8 insertions(+), 7 deletions(-)
> >
> > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > index 85615a3..e48a06f 100644
> > --- a/drivers/net/virtio_net.c
> > +++ b/drivers/net/virtio_net.c
> > @@ -563,7 +563,6 @@ static netdev_tx_t start_xmit(struct sk_buff *skb,
> > struct net_device *dev)
> > struct virtnet_info *vi = netdev_priv(dev);
> > int capacity;
> >
> > -again:
> > /* Free up any pending old buffers before queueing new ones. */
> > free_old_xmit_skbs(vi);
> >
> > @@ -572,12 +571,14 @@ again:
> >
> > /* This can happen with OOM and indirect buffers. */
> > if (unlikely(capacity < 0)) {
> > - netif_stop_queue(dev);
> > - dev_warn(&dev->dev, "Unexpected full queue\n");
> > - if (unlikely(!virtqueue_enable_cb(vi->svq))) {
> > - virtqueue_disable_cb(vi->svq);
> > - netif_start_queue(dev);
> > - goto again;
> > + if (net_ratelimit()) {
> > + if (likely(capacity == -ENOMEM))
> > + dev_warn(&dev->dev,
> > + "TX queue failure: out of memory\n");
> > + else
> > + dev_warn(&dev->dev,
> > + "Unexpected TX queue failure: %d\n",
> > + capacity);
> > }
> > return NETDEV_TX_BUSY;
> > }
>
> It is not clear to me how xmit_skb() can return -ENOMEM.
> xmit_skb() calls virtqueue_add_buf_gfp() which can return -ENOSPC.
> Even vring_add_indirect() doesn't return -ENOMEM on kmalloc failure.
It makes more sense to have the device increment tx_droppped,
and return NETDEV_TX_OK. Skip the message (or make it a pr_debug()).
Network devices do not guarantee packet delivery, and if out of
resources then holding more data in the
queue is going to hurt not help the situation.
--
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