On Mon, Mar 6, 2023 at 12:15 PM Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx> wrote:
>
> Separate the logic of checking whether sq is full. The subsequent patch
> will reuse this func.
>
> Signed-off-by: Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>
> ---
> drivers/net/virtio_net.c | 59 ++++++++++++++++++++++++----------------
> 1 file changed, 35 insertions(+), 24 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index fb5e68ed3ec2..777de0ec0b1b 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -1750,6 +1750,40 @@ static void free_old_xmit_skbs(struct send_queue *sq, bool in_napi)
> u64_stats_update_end(&sq->stats.syncp);
> }
>
> +static void check_sq_full(struct virtnet_info *vi, struct net_device *dev,
> + struct send_queue *sq)
> +{
Nit: we need a better name, it's not only the check but also can disable TX.
Thanks
> + bool use_napi = sq->napi.weight;
> + int qnum;
> +
> + qnum = sq - vi->sq;
> +
> + /* If running out of space, stop queue to avoid getting packets that we
> + * are then unable to transmit.
> + * An alternative would be to force queuing layer to requeue the skb by
> + * returning NETDEV_TX_BUSY. However, NETDEV_TX_BUSY should not be
> + * returned in a normal path of operation: it means that driver is not
> + * maintaining the TX queue stop/start state properly, and causes
> + * the stack to do a non-trivial amount of useless work.
> + * Since most packets only take 1 or 2 ring slots, stopping the queue
> + * early means 16 slots are typically wasted.
> + */
> + if (sq->vq->num_free < 2+MAX_SKB_FRAGS) {
> + netif_stop_subqueue(dev, qnum);
> + if (use_napi) {
> + if (unlikely(!virtqueue_enable_cb_delayed(sq->vq)))
> + virtqueue_napi_schedule(&sq->napi, sq->vq);
> + } else if (unlikely(!virtqueue_enable_cb_delayed(sq->vq))) {
> + /* More just got used, free them then recheck. */
> + free_old_xmit_skbs(sq, false);
> + if (sq->vq->num_free >= 2+MAX_SKB_FRAGS) {
> + netif_start_subqueue(dev, qnum);
> + virtqueue_disable_cb(sq->vq);
> + }
> + }
> + }
> +}
> +
> static bool is_xdp_raw_buffer_queue(struct virtnet_info *vi, int q)
> {
> if (q < (vi->curr_queue_pairs - vi->xdp_queue_pairs))
> @@ -1989,30 +2023,7 @@ static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device *dev)
> nf_reset_ct(skb);
> }
>
> - /* If running out of space, stop queue to avoid getting packets that we
> - * are then unable to transmit.
> - * An alternative would be to force queuing layer to requeue the skb by
> - * returning NETDEV_TX_BUSY. However, NETDEV_TX_BUSY should not be
> - * returned in a normal path of operation: it means that driver is not
> - * maintaining the TX queue stop/start state properly, and causes
> - * the stack to do a non-trivial amount of useless work.
> - * Since most packets only take 1 or 2 ring slots, stopping the queue
> - * early means 16 slots are typically wasted.
> - */
> - if (sq->vq->num_free < 2+MAX_SKB_FRAGS) {
> - netif_stop_subqueue(dev, qnum);
> - if (use_napi) {
> - if (unlikely(!virtqueue_enable_cb_delayed(sq->vq)))
> - virtqueue_napi_schedule(&sq->napi, sq->vq);
> - } else if (unlikely(!virtqueue_enable_cb_delayed(sq->vq))) {
> - /* More just got used, free them then recheck. */
> - free_old_xmit_skbs(sq, false);
> - if (sq->vq->num_free >= 2+MAX_SKB_FRAGS) {
> - netif_start_subqueue(dev, qnum);
> - virtqueue_disable_cb(sq->vq);
> - }
> - }
> - }
> + check_sq_full(vi, dev, sq);
>
> if (kick || netif_xmit_stopped(txq)) {
> if (virtqueue_kick_prepare(sq->vq) && virtqueue_notify(sq->vq)) {
> --
> 2.32.0.3.g01195cf9f
>
