xen-netback: split event channels support for Xen backend driver

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 equals to rx_irq.

Signed-off-by: Wei Liu <wei.liu2@citrix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 34 insertions, 7 deletions

diff --git a/drivers/net/xen-netback/xenbus.c b/drivers/net/xen-netback/xenbus.c
index d230c145660c..04bd860d16a9 100644
--- a/drivers/net/xen-netback/xenbus.c
+++ b/drivers/net/xen-netback/xenbus.c
@@ -122,6 +122,16 @@ static int netback_probe(struct xenbus_device *dev,
 		goto fail;
 	}
 
+	/*
+	 * Split event channels support, this is optional so it is not
+	 * put inside the above loop.
+	 */
+	err = xenbus_printf(XBT_NIL, dev->nodename,
+			    "feature-split-event-channels",
+			    "%u", separate_tx_rx_irq);
+	if (err)
+		pr_debug("Error writing feature-split-event-channels");
+
 	err = xenbus_switch_state(dev, XenbusStateInitWait);
 	if (err)
 		goto fail;
@@ -393,21 +403,36 @@ static int connect_rings(struct backend_info *be)
 	struct xenvif *vif = be->vif;
 	struct xenbus_device *dev = be->dev;
 	unsigned long tx_ring_ref, rx_ring_ref;
-	unsigned int evtchn, rx_copy;
+	unsigned int tx_evtchn, rx_evtchn, rx_copy;
 	int err;
 	int val;
 
 	err = xenbus_gather(XBT_NIL, dev->otherend,
 			    "tx-ring-ref", "%lu", &tx_ring_ref,
-			    "rx-ring-ref", "%lu", &rx_ring_ref,
-			    "event-channel", "%u", &evtchn, NULL);
+			    "rx-ring-ref", "%lu", &rx_ring_ref, NULL);
 	if (err) {
 		xenbus_dev_fatal(dev, err,
-				 "reading %s/ring-ref and event-channel",
+				 "reading %s/ring-ref",
 				 dev->otherend);
 		return err;
 	}
 
+	/* Try split event channels first, then single event channel. */
+	err = xenbus_gather(XBT_NIL, dev->otherend,
+			    "event-channel-tx", "%u", &tx_evtchn,
+			    "event-channel-rx", "%u", &rx_evtchn, NULL);
+	if (err < 0) {
+		err = xenbus_scanf(XBT_NIL, dev->otherend,
+				   "event-channel", "%u", &tx_evtchn);
+		if (err < 0) {
+			xenbus_dev_fatal(dev, err,
+					 "reading %s/event-channel(-tx/rx)",
+					 dev->otherend);
+			return err;
+		}
+		rx_evtchn = tx_evtchn;
+	}
+
 	err = xenbus_scanf(XBT_NIL, dev->otherend, "request-rx-copy", "%u",
 			   &rx_copy);
 	if (err == -ENOENT) {
@@ -454,11 +479,13 @@ static int connect_rings(struct backend_info *be)
 	vif->csum = !val;
 
 	/* Map the shared frame, irq etc. */
-	err = xenvif_connect(vif, tx_ring_ref, rx_ring_ref, evtchn);
+	err = xenvif_connect(vif, tx_ring_ref, rx_ring_ref,
+			     tx_evtchn, rx_evtchn);
 	if (err) {
 		xenbus_dev_fatal(dev, err,
-				 "mapping shared-frames %lu/%lu port %u",
-				 tx_ring_ref, rx_ring_ref, evtchn);
+				 "mapping shared-frames %lu/%lu port tx %u rx %u",
+				 tx_ring_ref, rx_ring_ref,
+				 tx_evtchn, rx_evtchn);
 		return err;
 	}
 	return 0;