[Xen-devel][PV-ops][PATCH 1/2] VNIF(netback): Using smart polling instead of event notification.

["Xu, Dongxiao" <dongxiao.xu@xxxxxxxxx>]

 - Netback will not notify netfront until it finds that the netfront has
stopped polling.
 - Netback will set a flag in xenstore to indicate whether netback 
supports the smart polling feature.  If there is only one side
supporting it, the communication mechanism will fall back to default,
and the new feature will not be used. The feature is enabled only
when both sides have the flag set in xenstore.

Signed-off-by: Dongxiao Xu <dongxiao.xu@xxxxxxxxx>
---
 drivers/xen/netback/common.h    |    2 ++
 drivers/xen/netback/netback.c   |   23 +++++++++++++++++++++--
 drivers/xen/netback/xenbus.c    |   16 ++++++++++++++++
 include/xen/interface/io/ring.h |    3 ++-
 4 files changed, 41 insertions(+), 3 deletions(-)

diff --git a/drivers/xen/netback/common.h b/drivers/xen/netback/common.h
index 9056be0..b15a7e1 100644
--- a/drivers/xen/netback/common.h
+++ b/drivers/xen/netback/common.h
@@ -76,6 +76,8 @@ struct xen_netif {
        /* Set of features that can be turned on in dev->features. */
        int features;
 
+       int smart_poll;
+
        /* Internal feature information. */
        u8 can_queue:1; /* can queue packets for receiver? */
 
diff --git a/drivers/xen/netback/netback.c b/drivers/xen/netback/netback.c
index d7d738e..869b6cc 100644
--- a/drivers/xen/netback/netback.c
+++ b/drivers/xen/netback/netback.c
@@ -640,7 +640,8 @@ static void net_rx_action(unsigned long unused)
 
                RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(&netif->rx, ret);
                irq = netif->irq;
-               if (ret && !rx_notify[irq]) {
+               if (ret && !rx_notify[irq] &&
+                               (netif->smart_poll != 1)) {
                        rx_notify[irq] = 1;
                        notify_list[notify_nr++] = irq;
                }
@@ -650,6 +651,16 @@ static void net_rx_action(unsigned long unused)
                    !netbk_queue_full(netif))
                        netif_wake_queue(netif->dev);
 
+               /* netfront_smartpoll_active indicates whether netfront timer 
+                 * is active.
+                 */
+               if ((netif->smart_poll == 1)) {
+                       if (!(netif->rx.sring->netfront_smartpoll_active)) {
+                               notify_remote_via_irq(irq);
+                               netif->rx.sring->netfront_smartpoll_active = 1;
+                       }
+               }
+
                netif_put(netif);
                dev_kfree_skb(skb);
                npo.meta_cons += nr_frags + 1;
@@ -1471,7 +1482,15 @@ static void make_tx_response(struct xen_netif *netif,
 
        netif->tx.rsp_prod_pvt = ++i;
        RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(&netif->tx, notify);
-       if (notify)
+       /* netfront_smartpoll_active indicates whether netfront timer is 
+         * active.
+         */
+       if ((netif->smart_poll == 1)) {
+               if (!(netif->rx.sring->netfront_smartpoll_active)) {
+                       notify_remote_via_irq(netif->irq);
+                       netif->rx.sring->netfront_smartpoll_active = 1;
+               }
+       } else if (notify)
                notify_remote_via_irq(netif->irq);
 }
 
diff --git a/drivers/xen/netback/xenbus.c b/drivers/xen/netback/xenbus.c
index a492288..3d8ed9a 100644
--- a/drivers/xen/netback/xenbus.c
+++ b/drivers/xen/netback/xenbus.c
@@ -115,6 +115,14 @@ static int netback_probe(struct xenbus_device *dev,
                        goto abort_transaction;
                }
 
+               /* We support data smart poll mechanism */
+               err = xenbus_printf(xbt, dev->nodename,
+                                   "feature-smart-poll", "%d", 1);
+               if (err) {
+                       message = "writing feature-smart-poll";
+                       goto abort_transaction;
+               }
+
                err = xenbus_transaction_end(xbt, 0);
        } while (err == -EAGAIN);
 
@@ -415,6 +423,14 @@ static int connect_rings(struct backend_info *be)
                be->netif->dev->features &= ~NETIF_F_IP_CSUM;
        }
 
+       if (xenbus_scanf(XBT_NIL, dev->otherend, "feature-smart-poll",
+                        "%d", &val) < 0)
+               val = 0;
+       if (val)
+               be->netif->smart_poll = 1;
+       else
+               be->netif->smart_poll = 0;
+
        /* Map the shared frame, irq etc. */
        err = netif_map(be->netif, tx_ring_ref, rx_ring_ref, evtchn);
        if (err) {
diff --git a/include/xen/interface/io/ring.h b/include/xen/interface/io/ring.h
index e8cbf43..865dcf0 100644
--- a/include/xen/interface/io/ring.h
+++ b/include/xen/interface/io/ring.h
@@ -73,7 +73,8 @@ union __name##_sring_entry {                                  
        \
 struct __name##_sring {                                                        
\
     RING_IDX req_prod, req_event;                                      \
     RING_IDX rsp_prod, rsp_event;                                      \
-    uint8_t  pad[48];                                                  \
+    uint8_t  netfront_smartpoll_active;                                        
\
+    uint8_t  pad[47];                                                  \
     union __name##_sring_entry ring[1]; /* variable-length */          \
 };                                                                     \
                                                                        \
-- 
1.6.3


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