Re: [Xen-devel] [PATCH v2 net-next 4/7] xen-netback: immediately wake tx queue when guest rx queue has space

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Tue, Oct 04, 2016 at 02:29:15AM -0700, Paul Durrant wrote:
> From: David Vrabel <david.vrabel@xxxxxxxxxx>
> 
> When an skb is removed from the guest rx queue, immediately wake the
> tx queue, instead of after processing them.

Please, could the description explain why?

> 
> Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>
> [re-based]
> Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
> ---
> Cc: Wei Liu <wei.liu2@xxxxxxxxxx>
> ---
>  drivers/net/xen-netback/rx.c | 24 ++++++++----------------
>  1 file changed, 8 insertions(+), 16 deletions(-)
> 
> diff --git a/drivers/net/xen-netback/rx.c b/drivers/net/xen-netback/rx.c
> index b0ce4c6..9548709 100644
> --- a/drivers/net/xen-netback/rx.c
> +++ b/drivers/net/xen-netback/rx.c
> @@ -92,27 +92,21 @@ static struct sk_buff *xenvif_rx_dequeue(struct 
> xenvif_queue *queue)
>       spin_lock_irq(&queue->rx_queue.lock);
>  
>       skb = __skb_dequeue(&queue->rx_queue);
> -     if (skb)
> +     if (skb) {
>               queue->rx_queue_len -= skb->len;
> +             if (queue->rx_queue_len < queue->rx_queue_max) {
> +                     struct netdev_queue *txq;
> +
> +                     txq = netdev_get_tx_queue(queue->vif->dev, queue->id);
> +                     netif_tx_wake_queue(txq);
> +             }
> +     }
>  
>       spin_unlock_irq(&queue->rx_queue.lock);
>  
>       return skb;
>  }
>  
> -static void xenvif_rx_queue_maybe_wake(struct xenvif_queue *queue)
> -{
> -     spin_lock_irq(&queue->rx_queue.lock);
> -
> -     if (queue->rx_queue_len < queue->rx_queue_max) {
> -             struct net_device *dev = queue->vif->dev;
> -
> -             netif_tx_wake_queue(netdev_get_tx_queue(dev, queue->id));
> -     }
> -
> -     spin_unlock_irq(&queue->rx_queue.lock);
> -}
> -
>  static void xenvif_rx_queue_purge(struct xenvif_queue *queue)
>  {
>       struct sk_buff *skb;
> @@ -585,8 +579,6 @@ int xenvif_kthread_guest_rx(void *data)
>                */
>               xenvif_rx_queue_drop_expired(queue);
>  
> -             xenvif_rx_queue_maybe_wake(queue);
> -
>               cond_resched();
>       }
>  
> -- 
> 2.1.4
> 
> 
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