On Thu, 25 Feb 2021 16:22:29 +0800
Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx> wrote:
> The number of queues implemented by many virtio backends is limited,
> especially some machines have a large number of CPUs. In this case, it
> is often impossible to allocate a separate queue for XDP_TX.
>
> This patch allows XDP_TX to run by reuse the existing SQ with
> __netif_tx_lock() hold when there are not enough queues.
>
> Signed-off-by: Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>
> Reviewed-by: Dust Li <dust.li@xxxxxxxxxxxxxxxxx>
> ---
> drivers/net/virtio_net.c | 48 ++++++++++++++++++++++++++++++++++++------------
> 1 file changed, 36 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
[...]
> @@ -2416,12 +2441,8 @@ static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog,
> xdp_qp = nr_cpu_ids;
>
> /* XDP requires extra queues for XDP_TX */
> - if (curr_qp + xdp_qp > vi->max_queue_pairs) {
> - NL_SET_ERR_MSG_MOD(extack, "Too few free TX rings available");
> - netdev_warn(dev, "request %i queues but max is %i\n",
> - curr_qp + xdp_qp, vi->max_queue_pairs);
> - return -ENOMEM;
> - }
> + if (curr_qp + xdp_qp > vi->max_queue_pairs)
> + xdp_qp = 0;
I think we should keep a netdev_warn message, but as a warning (not
error) that this will cause XDP_TX and XDP_REDIRECT to be slower on
this device due to too few free TX rings available.
In the future, we can mark a XDP features flag that this device is
operating in a slower "locked" Tx mode.
>
> old_prog = rtnl_dereference(vi->rq[0].xdp_prog);
> if (!prog && !old_prog)
--
Best regards,
Jesper Dangaard Brouer
MSc.CS, Principal Kernel Engineer at Red Hat
LinkedIn: http://www.linkedin.com/in/brouer
