netdev - Re: [PATCH] virtio_net: Fix queue full check

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Date:	Fri, 29 Oct 2010 16:25:09 +0530
From:	Krishna Kumar2 <krkumar2@...ibm.com>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	davem@...emloft.net, netdev@...r.kernel.org
Subject: Re: [PATCH] virtio_net: Fix queue full check

Rusty Russell <rusty@...tcorp.com.au> wrote on 10/29/2010 03:17:24 PM:

> > Oct 17 10:22:40 localhost kernel: net eth0: Unexpected TX queue
failure: -28
> > Oct 17 10:28:22 localhost kernel: net eth0: Unexpected TX queue
failure: -28
> > Oct 17 10:35:58 localhost kernel: net eth0: Unexpected TX queue
failure: -28
> > Oct 17 10:41:06 localhost kernel: net eth0: Unexpected TX queue
failure: -28
> >
> > I initially changed the check from -ENOMEM to -ENOSPC, but
> > virtqueue_add_buf can return only -ENOSPC when it doesn't have
> > space for new request.  Patch removes redundant checks but
> > displays the failure errno.
> >
> > Signed-off-by: Krishna Kumar <krkumar2@...ibm.com>
> > ---
> >  drivers/net/virtio_net.c |   15 ++++-----------
> >  1 file changed, 4 insertions(+), 11 deletions(-)
> >
> > diff -ruNp org/drivers/net/virtio_net.c new/drivers/net/virtio_net.c
> > --- org/drivers/net/virtio_net.c   2010-10-11 10:20:02.000000000 +0530
> > +++ new/drivers/net/virtio_net.c   2010-10-21 17:37:45.000000000 +0530
> > @@ -570,17 +570,10 @@ 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)) {
> > -            dev_warn(&dev->dev,
> > -                "TX queue failure: out of memory\n");
> > -         } else {
> > -            dev->stats.tx_fifo_errors++;
> > -            dev_warn(&dev->dev,
> > -                "Unexpected TX queue failure: %d\n",
> > -                capacity);
> > -         }
> > -      }
> > +      if (net_ratelimit())
> > +         dev_warn(&dev->dev,
> > +             "TX queue failure (%d): out of memory\n",
> > +             capacity);
>
> Hold on... you were getting -ENOSPC, which shouldn't happen.  What makes
you
> think it's out of memory?

virtqueue_add_buf_gfp returns only -ENOSPC on failure, whether
direct or indirect descriptors are used, so isn't -ENOSPC
"expected"? (vring_add_indirect returns -ENOMEM on memory
failure, but that is masked out and we go direct which is
the failure point).

Thanks,

- KK

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