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

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Konrad Rzeszutek Wilk [mailto:konrad.wilk@xxxxxxxxxx]
> Sent: 04 October 2016 13:49
> To: Paul Durrant <Paul.Durrant@xxxxxxxxxx>
> Cc: netdev@xxxxxxxxxxxxxxx; xen-devel@xxxxxxxxxxxxxxxxxxxx; Wei Liu
> <wei.liu2@xxxxxxxxxx>; David Vrabel <david.vrabel@xxxxxxxxxx>
> Subject: Re: [Xen-devel] [PATCH v2 net-next 4/7] xen-netback: immediately
> wake tx queue when guest rx queue has space
> 
> 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?
> 

Is it not reasonably obvious that it improves parallelism between filling and 
draining the queue? I could add a comment if you think it needs spelling out.

  Paul

> >
> > 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
> >
> >
> > _______________________________________________
> > Xen-devel mailing list
> > Xen-devel@xxxxxxxxxxxxx
> > https://lists.xen.org/xen-devel

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