Re: [PATCH RFC v2 2/4] virtio_net: disable cb aggressively

Jason Wang
2021-04-13T08:53:56Z

在 2021/4/13 下午1:47, Michael S. Tsirkin 写道:
> There are currently two cases where we poll TX vq not in response to a
> callback: start xmit and rx napi. We currently do this with callbacks
> enabled which can cause extra interrupts from the card. Used not to be
> a big issue as we run with interrupts disabled but that is no longer the
> case, and in some cases the rate of spurious interrupts is so high
> linux detects this and actually kills the interrupt.
>
> Fix up by disabling the callbacks before polling the tx vq.
>
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> ---
> drivers/net/virtio_net.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 82e520d2cb12..16d5abed582c 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -1429,6 +1429,7 @@ static void virtnet_poll_cleantx(struct receive_queue *rq)
> return;
>
> if (__netif_tx_trylock(txq)) {
> + virtqueue_disable_cb(sq->vq);
> free_old_xmit_skbs(sq, true);
> __netif_tx_unlock(txq);

Any reason that we don't need to enable the cb here?

And as we discussed in the past, it's probably the time to have a single
NAPI for both tx and rx?

Thanks

> }
> @@ -1582,6 +1583,7 @@ static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device *dev)
> bool use_napi = sq->napi.weight;
>
> /* Free up any pending old buffers before queueing new ones. */
> + virtqueue_disable_cb(sq->vq);
> free_old_xmit_skbs(sq, false);
>
> if (use_napi && kick)