Re: [Xen-devel] [PATCH net-next 1/2] xen-netback: split event channels feature support

[David Vrabel <david.vrabel@xxxxxxxxxx>]

On 21/05/13 00:02, Wei Liu wrote:
> Netback and netfront only use one event channel to do TX / RX notification,
> which may cause unnecessary wake-up of processing routines. This patch adds a
> new feature called feature-split-event-channels to netback, enabling it to
> handle TX and RX events separately.
> 
> Netback will use tx_irq to notify guest for TX completion, rx_irq for RX
> notification.
> 
> If frontend doesn't support this feature, tx_irq is equal to rx_irq.
[...]
> --- a/drivers/net/xen-netback/interface.c
> +++ b/drivers/net/xen-netback/interface.c
> @@ -69,12 +69,35 @@ static irqreturn_t xenvif_interrupt(int irq, void *dev_id)
>  
>       xen_netbk_schedule_xenvif(vif);
>  
> +     return IRQ_HANDLED;
> +}
> +
> +static irqreturn_t xenvif_rx_interrupt(int irq, void *dev_id)
> +{
> +     struct xenvif *vif = dev_id;
> +
> +     if (vif->netbk == NULL)
> +             return IRQ_NONE;

I know the original code had this but this looks suspect to me.  Event
channels are never shared so it does not make sense to ever return IRQ_NONE.

Suggest making this return IRQ_HANDLED instead (and similarly in
xenvif_tx_interrupt()) and...

> +static irqreturn_t xenvif_interrupt(int irq, void *dev_id)
> +{
> +     struct xenvif *vif = dev_id;
> +
> +     if (vif->netbk == NULL)
> +             return IRQ_NONE;

... then you can remove this test.

> --- a/drivers/net/xen-netback/xenbus.c
> +++ b/drivers/net/xen-netback/xenbus.c
> @@ -114,6 +114,15 @@ static int netback_probe(struct xenbus_device *dev,
>                       goto abort_transaction;
>               }
>  
> +             /* Split event channels support */
> +             err = xenbus_printf(xbt, dev->nodename,
> +                             "feature-split-event-channels",
> +                             "%u", 1);
> +             if (err) {
> +                     message = "writing feature-split-event-channels";
> +                     goto abort_transaction;
> +             }
> +

Event channels are currently a limited resource.  Do we want to have a
knob to disable this feature?

David

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