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From: Michael S. Tsirkin on 21 Jun 2010 04:40
On Mon, Jun 21, 2010 at 12:13:49PM +0930, Rusty Russell wrote:
> On Fri, 11 Jun 2010 04:33:43 am Michael S. Tsirkin wrote:
> > > > > @@ -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);
> ...
> >
> > Well, I only keep the existing behaviour around.
>
> Actually, it *does* change behavior, as the comment indicates. So let's
> fix the whole thing. AFAICT wth TX_BUSY we'll get called again RSN, and
> that's not really useful for OOM.
>
> This is what I have:
>
> Subject: virtio_net: fix oom handling on tx
> Date: Thu, 10 Jun 2010 18:20:41 +0300
> From: "Michael S. Tsirkin" <mst(a)redhat.com>
>
> 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 <mst(a)redhat.com>
> Signed-off-by: Rusty Russell <rusty(a)rustcorp.com.au> (...and avoid TX_BUSY)
> Cc: stable(a)kernel.org
> ---
> drivers/net/virtio_net.c | 18 ++++++++++--------
> 1 file changed, 10 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -562,7 +562,6 @@ static netdev_tx_t start_xmit(struct sk_
> 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);
>
> @@ -571,14 +570,17 @@ 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;
> + kfree_skb(skb);
> + return NETDEV_TX_OK;

If we do so, let's increment the dropped counter and/or error counter?

> }
> virtqueue_kick(vi->svq);
>
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From: Rusty Russell on 21 Jun 2010 06:30
On Mon, 21 Jun 2010 06:03:16 pm Michael S. Tsirkin wrote:
> On Mon, Jun 21, 2010 at 12:13:49PM +0930, Rusty Russell wrote:
> > - return NETDEV_TX_BUSY;
> > + kfree_skb(skb);
> > + return NETDEV_TX_OK;
>
> If we do so, let's increment the dropped counter and/or error counter?

Yep, here's the extra change:

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -571,14 +571,16 @@ static netdev_tx_t start_xmit(struct sk_
/* This can happen with OOM and indirect buffers. */
if (unlikely(capacity < 0)) {
if (net_ratelimit()) {
- if (likely(capacity == -ENOMEM))
+ if (likely(capacity == -ENOMEM)) {
dev_warn(&dev->dev,
"TX queue failure: out of memory\n");
- else
+ } else {
+ dev->stats.tx_fifo_errors++;
dev_warn(&dev->dev,
"Unexpected TX queue failure: %d\n",
capacity);
}
+ dev->stats.tx_dropped++;
kfree_skb(skb);
return NETDEV_TX_OK;
}
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From: Michael S. Tsirkin on 21 Jun 2010 07:00
On Mon, Jun 21, 2010 at 07:53:43PM +0930, Rusty Russell wrote:
> On Mon, 21 Jun 2010 06:03:16 pm Michael S. Tsirkin wrote:
> > On Mon, Jun 21, 2010 at 12:13:49PM +0930, Rusty Russell wrote:
> > > - return NETDEV_TX_BUSY;
> > > + kfree_skb(skb);
> > > + return NETDEV_TX_OK;
> >
> > If we do so, let's increment the dropped counter and/or error counter?
>
> Yep, here's the extra change:

Looks good to me.

> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -571,14 +571,16 @@ static netdev_tx_t start_xmit(struct sk_
> /* This can happen with OOM and indirect buffers. */
> if (unlikely(capacity < 0)) {
> if (net_ratelimit()) {
> - if (likely(capacity == -ENOMEM))
> + if (likely(capacity == -ENOMEM)) {
> dev_warn(&dev->dev,
> "TX queue failure: out of memory\n");
> - else
> + } else {
> + dev->stats.tx_fifo_errors++;
> dev_warn(&dev->dev,
> "Unexpected TX queue failure: %d\n",
> capacity);
> }
> + dev->stats.tx_dropped++;
> kfree_skb(skb);
> return NETDEV_TX_OK;
> }
--
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