On 5/26/21 10:24 AM, Michael S. Tsirkin wrote:
> 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.
It is not clear why we want to poll TX completions from ndo_start_xmit() in napi mode ?
This seems not needed, adding costs to sender thread, this might
reduce the ability to use a different cpu for tx completions.
Also this will likely conflict with BQL model if we want to use BQL at some point.
>
This probably needs a Fixes: tag
> Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
> ---
> drivers/net/virtio_net.c | 16 ++++++++++++----
> 1 file changed, 12 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index c29f42d1e04f..a83dc038d8af 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -1433,7 +1433,10 @@ static void virtnet_poll_cleantx(struct receive_queue *rq)
> return;
>
> if (__netif_tx_trylock(txq)) {
> - free_old_xmit_skbs(sq, true);
> + do {
> + virtqueue_disable_cb(sq->vq);
> + free_old_xmit_skbs(sq, true);
> + } while (unlikely(!virtqueue_enable_cb_delayed(sq->vq)));
>
> if (sq->vq->num_free >= 2 + MAX_SKB_FRAGS)
> netif_tx_wake_queue(txq);
> @@ -1605,12 +1608,17 @@ static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device *dev)
> struct netdev_queue *txq = netdev_get_tx_queue(dev, qnum);
> bool kick = !netdev_xmit_more();
> bool use_napi = sq->napi.weight;
> + unsigned int bytes = skb->len;
>
> /* Free up any pending old buffers before queueing new ones. */
> - free_old_xmit_skbs(sq, false);
> + do {
> + if (use_napi)
> + virtqueue_disable_cb(sq->vq);
>
> - if (use_napi && kick)
> - virtqueue_enable_cb_delayed(sq->vq);
> + free_old_xmit_skbs(sq, false);
> +
> + } while (use_napi && kick &&
> + unlikely(!virtqueue_enable_cb_delayed(sq->vq)));
>
> /* timestamp packet in software */
> skb_tx_timestamp(skb);
>
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