On Wed, May 1, 2024 at 4:07 AM Michael S. Tsirkin <mst@xxxxxxxxxx> wrote:
>
> On Tue, Apr 30, 2024 at 03:35:09PM -0400, Darius Rad wrote:
> > The transmit queue is stopped when the number of free queue entries is less
> > than 2+MAX_SKB_FRAGS, in start_xmit(). If the queue length (QUEUE_NUM_MAX)
> > is less than then this, transmission will immediately trigger a netdev
> > watchdog timeout. Report this condition earlier and more directly.
> >
> > Signed-off-by: Darius Rad <darius@xxxxxxxxxxxx>
> > ---
> > drivers/net/virtio_net.c | 3 +++
> > 1 file changed, 3 insertions(+)
> >
> > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > index 115c3c5414f2..72ee8473b61c 100644
> > --- a/drivers/net/virtio_net.c
> > +++ b/drivers/net/virtio_net.c
> > @@ -4917,6 +4917,9 @@ static int virtnet_probe(struct virtio_device *vdev)
> > set_bit(guest_offloads[i], &vi->guest_offloads);
> > vi->guest_offloads_capable = vi->guest_offloads;
> >
> > + if (virtqueue_get_vring_size(vi->sq->vq) < 2 + MAX_SKB_FRAGS)
> > + netdev_warn_once(dev, "not enough queue entries, expect xmit timeout\n");
> > +
>
> How about actually fixing it though? E.g. by linearizing...
Actually, the linearing is only needed for the case when the indirect
descriptor is not supported.
>
> It also bothers me that there's practically
> /proc/sys/net/core/max_skb_frags
> and if that's low then things could actually work.
Probably not as it won't exceed MAX_SKB_FRAGS.
>
> Finally, while originally it was just 17 typically, now it's
> configurable. So it's possible that you change the config to make big
> tcp
Note that virtio-net doesn't fully support big TCP.
> work better and device stops working while it worked fine
> previously.
For this patch, I guess not as we had:
if (sq->vq->num_free < 2+MAX_SKB_FRAGS)
in the tx path. So it won't even work before this patch.
Thanks
>
>
> > pr_debug("virtnet: registered device %s with %d RX and TX vq's\n",
> > dev->name, max_queue_pairs);
> >
> > --
> > 2.39.2
>
