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[Xen-devel] [PATCH 7/8] netback: split event channels support



Netback and netfront only use one event channel to do tx / rx notification.
This may cause unnecessary wake-up of process routines. This patch adds a new
feature called feautre-split-event-channel to netback, enabling it to handle
Tx and Rx event 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 = rx_irq.

Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
---
 drivers/net/xen-netback/common.h    |   10 +++--
 drivers/net/xen-netback/interface.c |   78 ++++++++++++++++++++++++++++-------
 drivers/net/xen-netback/netback.c   |    7 ++--
 drivers/net/xen-netback/xenbus.c    |   44 ++++++++++++++++----
 4 files changed, 109 insertions(+), 30 deletions(-)

diff --git a/drivers/net/xen-netback/common.h b/drivers/net/xen-netback/common.h
index f541ba9..cc2a9f0 100644
--- a/drivers/net/xen-netback/common.h
+++ b/drivers/net/xen-netback/common.h
@@ -63,8 +63,11 @@ struct xenvif {
 
        u8               fe_dev_addr[6];
 
-       /* Physical parameters of the comms window. */
-       unsigned int     irq;
+       /* Physical parameters of the comms window.
+        * When feature-split-event-channels = 0, tx_irq = rx_irq.
+        */
+       unsigned int tx_irq;
+       unsigned int rx_irq;
 
        /* List of frontends to notify after a batch of frames sent. */
        struct list_head notify_list;
@@ -122,10 +125,11 @@ struct xenvif *xenvif_alloc(struct device *parent,
                            domid_t domid,
                            unsigned int handle);
 
+/* When feature-split-event-channels == 0, tx_evtchn == rx_evtchn */
 int xenvif_connect(struct xenvif *vif,
                   unsigned long *tx_ring_ref, unsigned int tx_ring_order,
                   unsigned long *rx_ring_ref, unsigned int rx_ring_order,
-                  unsigned int evtchn);
+                  unsigned int tx_evtchn, unsigned int rx_evtchn);
 void xenvif_disconnect(struct xenvif *vif);
 
 void xenvif_get(struct xenvif *vif);
diff --git a/drivers/net/xen-netback/interface.c 
b/drivers/net/xen-netback/interface.c
index fa4d46d..c9ebe21 100644
--- a/drivers/net/xen-netback/interface.c
+++ b/drivers/net/xen-netback/interface.c
@@ -60,7 +60,8 @@ static int xenvif_rx_schedulable(struct xenvif *vif)
        return xenvif_schedulable(vif) && !xen_netbk_rx_ring_full(vif);
 }
 
-static irqreturn_t xenvif_interrupt(int irq, void *dev_id)
+/* Tx interrupt handler used when feature-split-event-channels == 1 */
+static irqreturn_t xenvif_tx_interrupt(int tx_irq, void *dev_id)
 {
        struct xenvif *vif = dev_id;
 
@@ -69,12 +70,31 @@ static irqreturn_t xenvif_interrupt(int irq, void *dev_id)
 
        xen_netbk_schedule_xenvif(vif);
 
+       return IRQ_HANDLED;
+}
+
+/* Rx interrupt handler used when feature-split-event-channels == 1 */
+static irqreturn_t xenvif_rx_interrupt(int rx_irq, void *dev_id)
+{
+       struct xenvif *vif = dev_id;
+
+       if (vif->netbk == NULL)
+               return IRQ_NONE;
+
        if (xenvif_rx_schedulable(vif))
                netif_wake_queue(vif->dev);
 
        return IRQ_HANDLED;
 }
 
+/* Used when feature-split-event-channels == 0 */
+static irqreturn_t xenvif_interrupt(int irq, void *dev_id)
+{
+       xenvif_tx_interrupt(irq, dev_id);
+       xenvif_rx_interrupt(irq, dev_id);
+       return IRQ_HANDLED;
+}
+
 static int xenvif_start_xmit(struct sk_buff *skb, struct net_device *dev)
 {
        struct xenvif *vif = netdev_priv(dev);
@@ -125,13 +145,15 @@ static struct net_device_stats *xenvif_get_stats(struct 
net_device *dev)
 static void xenvif_up(struct xenvif *vif)
 {
        xen_netbk_add_xenvif(vif);
-       enable_irq(vif->irq);
+       enable_irq(vif->tx_irq);
+       enable_irq(vif->rx_irq);
        xen_netbk_check_rx_xenvif(vif);
 }
 
 static void xenvif_down(struct xenvif *vif)
 {
-       disable_irq(vif->irq);
+       disable_irq(vif->tx_irq);
+       disable_irq(vif->rx_irq);
        del_timer_sync(&vif->credit_timeout);
        xen_netbk_deschedule_xenvif(vif);
        xen_netbk_remove_xenvif(vif);
@@ -308,7 +330,7 @@ struct xenvif *xenvif_alloc(struct device *parent, domid_t 
domid,
 int xenvif_connect(struct xenvif *vif,
                   unsigned long *tx_ring_ref, unsigned int tx_ring_ref_count,
                   unsigned long *rx_ring_ref, unsigned int rx_ring_ref_count,
-                  unsigned int evtchn)
+                  unsigned int tx_evtchn, unsigned int rx_evtchn)
 {
        int err = -ENOMEM;
        void *addr;
@@ -317,7 +339,7 @@ int xenvif_connect(struct xenvif *vif,
        int tmp[NETBK_MAX_RING_PAGES], i;
 
        /* Already connected through? */
-       if (vif->irq)
+       if (vif->tx_irq)
                return 0;
 
        __module_get(THIS_MODULE);
@@ -347,13 +369,32 @@ int xenvif_connect(struct xenvif *vif,
        BACK_RING_INIT(&vif->rx, rxs, PAGE_SIZE * rx_ring_ref_count);
        vif->nr_rx_handles = rx_ring_ref_count;
 
-       err = bind_interdomain_evtchn_to_irqhandler(
-               vif->domid, evtchn, xenvif_interrupt, 0,
-               vif->dev->name, vif);
-       if (err < 0)
-               goto err_rx_unmap;
-       vif->irq = err;
-       disable_irq(vif->irq);
+       if (tx_evtchn == rx_evtchn) { /* feature-split-event-channels == 0 */
+               err = bind_interdomain_evtchn_to_irqhandler(
+                       vif->domid, tx_evtchn, xenvif_interrupt, 0,
+                       vif->dev->name, vif);
+               if (err < 0)
+                       goto err_rx_unmap;
+               vif->tx_irq = vif->rx_irq = err;
+               disable_irq(vif->tx_irq);
+               disable_irq(vif->rx_irq);
+       } else { /* feature-split-event-channels == 1 */
+               err = bind_interdomain_evtchn_to_irqhandler(
+                       vif->domid, tx_evtchn, xenvif_tx_interrupt, 0,
+                       vif->dev->name, vif);
+               if (err < 0)
+                       goto err_rx_unmap;
+               vif->tx_irq = err;
+               disable_irq(vif->tx_irq);
+
+               err = bind_interdomain_evtchn_to_irqhandler(
+                       vif->domid, rx_evtchn, xenvif_rx_interrupt, 0,
+                       vif->dev->name, vif);
+               if (err < 0)
+                       goto err_tx_unbind;
+               vif->rx_irq = err;
+               disable_irq(vif->rx_irq);
+       }
 
        xenvif_get(vif);
 
@@ -367,6 +408,10 @@ int xenvif_connect(struct xenvif *vif,
        rtnl_unlock();
 
        return 0;
+
+err_tx_unbind:
+       unbind_from_irqhandler(vif->tx_irq, vif);
+       vif->tx_irq = 0;
 err_rx_unmap:
        xen_netbk_unmap_frontend_rings(vif, (void *)vif->rx.sring);
        vif->nr_rx_handles = 0;
@@ -406,8 +451,13 @@ void xenvif_disconnect(struct xenvif *vif)
        atomic_dec(&vif->refcnt);
        wait_event(vif->waiting_to_free, atomic_read(&vif->refcnt) == 0);
 
-       if (vif->irq) {
-               unbind_from_irqhandler(vif->irq, vif);
+       if (vif->tx_irq) {
+               if (vif->tx_irq == vif->rx_irq)
+                       unbind_from_irqhandler(vif->tx_irq, vif);
+               else {
+                       unbind_from_irqhandler(vif->tx_irq, vif);
+                       unbind_from_irqhandler(vif->rx_irq, vif);
+               }
                need_module_put = 1;
        }
 
diff --git a/drivers/net/xen-netback/netback.c 
b/drivers/net/xen-netback/netback.c
index 644c760..5ac8c35 100644
--- a/drivers/net/xen-netback/netback.c
+++ b/drivers/net/xen-netback/netback.c
@@ -639,7 +639,7 @@ static void xen_netbk_rx_action(struct xen_netbk *netbk)
 {
        struct xenvif *vif = NULL, *tmp;
        s8 status;
-       u16 irq, flags;
+       u16 flags;
        struct xen_netif_rx_response *resp;
        struct sk_buff_head rxq;
        struct sk_buff *skb;
@@ -750,7 +750,6 @@ static void xen_netbk_rx_action(struct xen_netbk *netbk)
                                         sco->meta_slots_used);
 
                RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(&vif->rx, ret);
-               irq = vif->irq;
                if (ret && list_empty(&vif->notify_list))
                        list_add_tail(&vif->notify_list, &notify);
 
@@ -762,7 +761,7 @@ static void xen_netbk_rx_action(struct xen_netbk *netbk)
        }
 
        list_for_each_entry_safe(vif, tmp, &notify, notify_list) {
-               notify_remote_via_irq(vif->irq);
+               notify_remote_via_irq(vif->rx_irq);
                list_del_init(&vif->notify_list);
        }
 
@@ -1595,7 +1594,7 @@ static void make_tx_response(struct xenvif *vif,
        vif->tx.rsp_prod_pvt = ++i;
        RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(&vif->tx, notify);
        if (notify)
-               notify_remote_via_irq(vif->irq);
+               notify_remote_via_irq(vif->tx_irq);
 }
 
 static struct xen_netif_rx_response *make_rx_response(struct xenvif *vif,
diff --git a/drivers/net/xen-netback/xenbus.c b/drivers/net/xen-netback/xenbus.c
index 1791807..6822d89 100644
--- a/drivers/net/xen-netback/xenbus.c
+++ b/drivers/net/xen-netback/xenbus.c
@@ -141,6 +141,15 @@ 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;
+               }
+
                err = xenbus_transaction_end(xbt, 0);
        } while (err == -EAGAIN);
 
@@ -419,7 +428,7 @@ static int connect_rings(struct backend_info *be)
 {
        struct xenvif *vif = be->vif;
        struct xenbus_device *dev = be->dev;
-       unsigned int evtchn, rx_copy;
+       unsigned int tx_evtchn, rx_evtchn, rx_copy;
        int err;
        int val;
        unsigned long tx_ring_ref[NETBK_MAX_RING_PAGES];
@@ -428,12 +437,22 @@ static int connect_rings(struct backend_info *be)
        unsigned int  rx_ring_order;
 
        err = xenbus_gather(XBT_NIL, dev->otherend,
-                           "event-channel", "%u", &evtchn, NULL);
+                           "event-channel", "%u", &tx_evtchn, NULL);
        if (err) {
-               xenbus_dev_fatal(dev, err,
-                                "reading %s/event-channel",
-                                dev->otherend);
-               return err;
+               /* try split event channels */
+               err = xenbus_gather(XBT_NIL, dev->otherend,
+                                   "event-channel-tx", "%u", &tx_evtchn,
+                                   "event-channel-rx", "%u", &rx_evtchn,
+                                   NULL);
+               if (err) {
+                       xenbus_dev_fatal(dev, err,
+                                        "reading %s/event-channel(-tx/rx)",
+                                        dev->otherend);
+                       return err;
+               }
+       } else { /* frontend doesn't support split event channels */
+               rx_evtchn = tx_evtchn;
+               dev_info(&dev->dev, "single event channel\n");
        }
 
        err = xenbus_scanf(XBT_NIL, dev->otherend, "tx-ring-order", "%u",
@@ -568,12 +587,19 @@ static int connect_rings(struct backend_info *be)
        /* Map the shared frame, irq etc. */
        err = xenvif_connect(vif, tx_ring_ref, (1U << tx_ring_order),
                             rx_ring_ref, (1U << rx_ring_order),
-                            evtchn);
+                            tx_evtchn, rx_evtchn);
        if (err) {
                /* construct 1 2 3 / 4 5 6 */
                int i;
                char txs[3 * (1U << MODPARM_netback_max_tx_ring_page_order)];
                char rxs[3 * (1U << MODPARM_netback_max_rx_ring_page_order)];
+               char evtchns[20];
+
+               if (tx_evtchn == rx_evtchn)
+                       snprintf(evtchns, sizeof(evtchns)-1, "%u", tx_evtchn);
+               else
+                       snprintf(evtchns, sizeof(evtchns)-1, "%u/%u",
+                                tx_evtchn, rx_evtchn);
 
                txs[0] = rxs[0] = 0;
 
@@ -586,8 +612,8 @@ static int connect_rings(struct backend_info *be)
                                 " %lu", rx_ring_ref[i]);
 
                xenbus_dev_fatal(dev, err,
-                                "mapping shared-frames%s /%s port %u",
-                                txs, rxs, evtchn);
+                                "mapping shared-frames%s /%s port %s",
+                                txs, rxs, evtchns);
                return err;
        }
        return 0;
-- 
1.7.10.4


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