Subject: Re: [PATCH 8/8] netfront: split event channels support

From: Konrad Rzeszutek Wilk <[email-masked]>
Date: Mon, 4 Mar 2013 16:24:16 -0500

On Fri, Feb 15, 2013 at 04:00:09PM +0000, Wei Liu wrote:
> If this feature is not activated, rx_irq = tx_irq. See corresponding netback
> change log for details.

To make it easier for people that use 'git log --grep' one usually says:
"See xen/netfront: Use .. " for the frontend implementation. That way
you can just copy-n-paste the title of the patch in the search functionality.

You should also include in this patch the description of the protocol.

And explain how it benefits the networking subsystem?

> 
> Signed-off-by: Wei Liu <[email-masked]>
> ---
>  drivers/net/xen-netfront.c |  184 ++++++++++++++++++++++++++++++++++++--------
>  1 file changed, 152 insertions(+), 32 deletions(-)
> 
> diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
> index de73a71..ea9b656 100644
> --- a/drivers/net/xen-netfront.c
> +++ b/drivers/net/xen-netfront.c
> @@ -100,7 +100,12 @@ struct netfront_info {
>  
>  	struct napi_struct napi;
>  
> -	unsigned int evtchn;
> +	/* 
> +	 * Split event channels support, tx_* == rx_* when using
> +	 * single event channel.
> +	 */
> +	unsigned int tx_evtchn, rx_evtchn;
> +	unsigned int tx_irq, rx_irq;
>  	struct xenbus_device *xbdev;
>  
>  	spinlock_t   tx_lock;
> @@ -344,7 +349,7 @@ no_skb:
>   push:
>  	RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(&np->rx, notify);
>  	if (notify)
> -		notify_remote_via_irq(np->netdev->irq);
> +		notify_remote_via_irq(np->rx_irq);
>  }
>  
>  static int xennet_open(struct net_device *dev)
> @@ -633,7 +638,7 @@ static int xennet_start_xmit(struct sk_buff *skb, struct net_device *dev)
>  
>  	RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(&np->tx, notify);
>  	if (notify)
> -		notify_remote_via_irq(np->netdev->irq);
> +		notify_remote_via_irq(np->tx_irq);
>  
>  	u64_stats_update_begin(&stats->syncp);
>  	stats->tx_bytes += skb->len;
> @@ -1263,26 +1268,41 @@ static int xennet_set_features(struct net_device *dev,
>  	return 0;
>  }
>  
> -static irqreturn_t xennet_interrupt(int irq, void *dev_id)
> +/* Used for tx completion */
> +static irqreturn_t xennet_tx_interrupt(int tx_irq, void *dev_id)
>  {
> -	struct net_device *dev = dev_id;
> -	struct netfront_info *np = netdev_priv(dev);
> +	struct netfront_info *np = dev_id;
> +	struct net_device *dev = np->netdev;
>  	unsigned long flags;
>  
>  	spin_lock_irqsave(&np->tx_lock, flags);
> +	xennet_tx_buf_gc(dev);
> +	spin_unlock_irqrestore(&np->tx_lock, flags);
>  
> -	if (likely(netif_carrier_ok(dev))) {
> -		xennet_tx_buf_gc(dev);
> -		/* Under tx_lock: protects access to rx shared-ring indexes. */
> -		if (RING_HAS_UNCONSUMED_RESPONSES(&np->rx))
> -			napi_schedule(&np->napi);
> -	}
> +	return IRQ_HANDLED;
> +}
>  
> -	spin_unlock_irqrestore(&np->tx_lock, flags);
> +/* Used for rx */
> +static irqreturn_t xennet_rx_interrupt(int rx_irq, void *dev_id)
> +{
> +	struct netfront_info *np = dev_id;
> +	struct net_device *dev = np->netdev;
> +
> +	if (likely(netif_carrier_ok(dev) &&
> +		   RING_HAS_UNCONSUMED_RESPONSES(&np->rx)))
> +		napi_schedule(&np->napi);
>  
>  	return IRQ_HANDLED;
>  }
>  
> +/* Used for single event channel configuration */
> +static irqreturn_t xennet_interrupt(int irq, void *dev_id)
> +{
> +	xennet_tx_interrupt(irq, dev_id);
> +	xennet_rx_interrupt(irq, dev_id);
> +	return IRQ_HANDLED;
> +}
> +
>  #ifdef CONFIG_NET_POLL_CONTROLLER
>  static void xennet_poll_controller(struct net_device *dev)
>  {
> @@ -1451,9 +1471,14 @@ static void xennet_disconnect_backend(struct netfront_info *info)
>  	spin_unlock_irq(&info->tx_lock);
>  	spin_unlock_bh(&info->rx_lock);
>  
> -	if (info->netdev->irq)
> -		unbind_from_irqhandler(info->netdev->irq, info->netdev);
> -	info->evtchn = info->netdev->irq = 0;
> +	if (info->tx_irq && (info->tx_irq == info->rx_irq))
> +		unbind_from_irqhandler(info->tx_irq, info);
> +	if (info->tx_irq && (info->tx_irq != info->rx_irq)) {
> +		unbind_from_irqhandler(info->tx_irq, info);
> +		unbind_from_irqhandler(info->rx_irq, info);
> +	}
> +	info->tx_evtchn = info->rx_evtchn = 0;
> +	info->tx_irq = info->rx_irq = 0;
>  
>  	xenbus_unmap_ring_vfree(info->xbdev, (void *)info->tx.sring);
>  	free_pages((unsigned long)info->tx.sring, info->tx_ring_page_order);
> @@ -1503,11 +1528,86 @@ static int xen_net_read_mac(struct xenbus_device *dev, u8 mac[])
>  	return 0;
>  }
>  
> +static int setup_netfront_single(struct netfront_info *info)
> +{
> +	int err;
> +
> +	err = xenbus_alloc_evtchn(info->xbdev, &info->tx_evtchn);
> +	if (err < 0)
> +		goto fail;
> +
> +	err = bind_evtchn_to_irqhandler(info->tx_evtchn,
> +					xennet_interrupt,
> +					0, info->netdev->name, info);
> +	if (err < 0)
> +		goto bind_fail;
> +	info->rx_evtchn = info->tx_evtchn;
> +	info->rx_irq = info->tx_irq = err;
> +	dev_info(&info->xbdev->dev,
> +		 "single event channel, evtchn = %d, irq = %d\n",
> +		 info->tx_evtchn, info->tx_irq);
> +
> +	return 0;
> +
> +bind_fail:
> +	xenbus_free_evtchn(info->xbdev, info->tx_evtchn);
> +	info->tx_evtchn = 0;
> +fail:
> +	return err;
> +}
> +
> +static int setup_netfront_split(struct netfront_info *info)
> +{
> +	int err;
> +
> +	err = xenbus_alloc_evtchn(info->xbdev, &info->tx_evtchn);
> +	if (err)
> +		goto fail;
> +	err = xenbus_alloc_evtchn(info->xbdev, &info->rx_evtchn);
> +	if (err)
> +		goto alloc_rx_evtchn_fail;
> +
> +	err = bind_evtchn_to_irqhandler(info->tx_evtchn,
> +					xennet_tx_interrupt,
> +					0, info->netdev->name, info);
> +	if (err < 0)
> +		goto bind_tx_fail;
> +	info->tx_irq = err;
> +
> +	err = bind_evtchn_to_irqhandler(info->rx_evtchn,
> +					xennet_rx_interrupt,
> +					0, info->netdev->name, info);
> +	if (err < 0)
> +		goto bind_rx_fail;
> +
> +	info->rx_irq = err;
> +
> +	dev_info(&info->xbdev->dev,
> +		 "split event channels, tx_evtchn/irq = %d/%d, rx_evtchn/irq = %d/%d",
> +		 info->tx_evtchn, info->tx_irq,
> +		 info->rx_evtchn, info->rx_irq);
> +
> +	return 0;
> +
> +bind_rx_fail:
> +	unbind_from_irqhandler(info->tx_irq, info);
> +	info->tx_irq = 0;
> +bind_tx_fail:
> +	xenbus_free_evtchn(info->xbdev, info->rx_evtchn);
> +	info->rx_evtchn = 0;
> +alloc_rx_evtchn_fail:
> +	xenbus_free_evtchn(info->xbdev, info->tx_evtchn);
> +	info->tx_evtchn = 0;
> +fail:
> +	return err;
> +}
> +
>  static int setup_netfront(struct xenbus_device *dev, struct netfront_info *info)
>  {
>  	struct xen_netif_tx_sring *txs;
>  	struct xen_netif_rx_sring *rxs;
>  	int err;
> +	unsigned int feature_split_evtchn;
>  	struct net_device *netdev = info->netdev;
>  	unsigned int max_tx_ring_page_order, max_rx_ring_page_order;
>  	int i;
> @@ -1527,6 +1627,12 @@ static int setup_netfront(struct xenbus_device *dev, struct netfront_info *info)
>  	}
>  
>  	err = xenbus_scanf(XBT_NIL, info->xbdev->otherend,
> +			   "feature-split-event-channels", "%u",
> +			   &feature_split_evtchn);
> +	if (err < 0)
> +		feature_split_evtchn = 0;
> +
> +	err = xenbus_scanf(XBT_NIL, info->xbdev->otherend,
>  			   "max-tx-ring-page-order", "%u",
>  			   &max_tx_ring_page_order);
>  	if (err < 0) {
> @@ -1598,20 +1704,17 @@ static int setup_netfront(struct xenbus_device *dev, struct netfront_info *info)
>  	if (err < 0)
>  		goto grant_rx_ring_fail;
>  
> -	err = xenbus_alloc_evtchn(dev, &info->evtchn);
> +	if (feature_split_evtchn)
> +		err = setup_netfront_split(info);
> +	else
> +		err = setup_netfront_single(info);
> +
>  	if (err)
> -		goto alloc_evtchn_fail;
> +		goto setup_evtchn_fail;
>  
> -	err = bind_evtchn_to_irqhandler(info->evtchn, xennet_interrupt,
> -					0, netdev->name, netdev);
> -	if (err < 0)
> -		goto bind_fail;
> -	netdev->irq = err;
>  	return 0;
>  
> -bind_fail:
> -	xenbus_free_evtchn(dev, info->evtchn);
> -alloc_evtchn_fail:
> +setup_evtchn_fail:
>  	xenbus_unmap_ring_vfree(info->xbdev, (void *)info->rx.sring);
>  grant_rx_ring_fail:
>  	free_pages((unsigned long)info->rx.sring, info->rx_ring_page_order);
> @@ -1696,11 +1799,26 @@ again:
>  		}
>  	}
>  
> -	err = xenbus_printf(xbt, dev->nodename,
> -			    "event-channel", "%u", info->evtchn);
> -	if (err) {
> -		message = "writing event-channel";
> -		goto abort_transaction;
> +	if (info->tx_evtchn == info->rx_evtchn) {
> +		err = xenbus_printf(xbt, dev->nodename,
> +				    "event-channel", "%u", info->tx_evtchn);
> +		if (err) {
> +			message = "writing event-channel";
> +			goto abort_transaction;
> +		}
> +	} else {
> +		err = xenbus_printf(xbt, dev->nodename,
> +				    "event-channel-tx", "%u", info->tx_evtchn);
> +		if (err) {
> +			message = "writing event-channel-tx";
> +			goto abort_transaction;
> +		}
> +		err = xenbus_printf(xbt, dev->nodename,
> +				    "event-channel-rx", "%u", info->rx_evtchn);
> +		if (err) {
> +			message = "writing event-channel-rx";
> +			goto abort_transaction;
> +		}
>  	}
>  
>  	err = xenbus_printf(xbt, dev->nodename, "request-rx-copy", "%u",
> @@ -1814,7 +1932,9 @@ static int xennet_connect(struct net_device *dev)
>  	 * packets.
>  	 */
>  	netif_carrier_on(np->netdev);
> -	notify_remote_via_irq(np->netdev->irq);
> +	notify_remote_via_irq(np->tx_irq);
> +	if (np->tx_irq != np->rx_irq)
> +		notify_remote_via_irq(np->rx_irq);
>  	xennet_tx_buf_gc(dev);
>  	xennet_alloc_rx_buffers(dev);
>  
> -- 
> 1.7.10.4
>