[win-pv-devel] [PATCH] Don't bump the receiver event counter if the poller is going to retry

[Paul Durrant <paul.durrant@xxxxxxxxxx>]

There is little point in bumping rsp_event (to trigger a new event from
the backend) if the poller is going to retry, so we can save modifying the
shared ring in this case.

This patch also adds extra debug code to the poller to make sure it never
exits from the main loop until either there are no retries pending or
the instance has been disabled.

Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
---
 src/xenvif/poller.c   | 26 +++++++++++++++-----------
 src/xenvif/receiver.c |  9 +++++++--
 2 files changed, 22 insertions(+), 13 deletions(-)

diff --git a/src/xenvif/poller.c b/src/xenvif/poller.c
index 6ff2c8c..cc7e68f 100644
--- a/src/xenvif/poller.c
+++ b/src/xenvif/poller.c
@@ -551,6 +551,9 @@ PollerInstanceDpc(
     PXENVIF_POLLER_INSTANCE Instance = Context;
     PXENVIF_POLLER          Poller;
     PXENVIF_FRONTEND        Frontend;
+    BOOLEAN                 Enabled;
+    BOOLEAN                 ReceiverRetry;
+    BOOLEAN                 TransmitterRetry;
 
     UNREFERENCED_PARAMETER(Dpc);
     UNREFERENCED_PARAMETER(Argument1);
@@ -560,9 +563,11 @@ PollerInstanceDpc(
 
     Poller = Instance->Poller;
     Frontend = Poller->Frontend;
+    Enabled = FALSE;
+    ReceiverRetry = FALSE;
+    TransmitterRetry = FALSE;
 
     for (;;) {
-        BOOLEAN Enabled;
         BOOLEAN NeedReceiverPoll;
         BOOLEAN NeedTransmitterPoll;
         KIRQL   Irql;
@@ -591,14 +596,12 @@ PollerInstanceDpc(
 
         if (NeedReceiverPoll)
         {
-            BOOLEAN Retry;
-
             KeRaiseIrql(DISPATCH_LEVEL, &Irql);
 
-            Retry = ReceiverPoll(FrontendGetReceiver(Frontend),
-                                 Instance->Index);
+            ReceiverRetry = ReceiverPoll(FrontendGetReceiver(Frontend),
+                                         Instance->Index);
 
-            if (!Retry) {
+            if (!ReceiverRetry) {
                 PollerInstanceUnmask(Instance, XENVIF_POLLER_EVENT_RECEIVE);
             } else {
                 (VOID) InterlockedBitTestAndSet(&Instance->Pending,
@@ -610,14 +613,12 @@ PollerInstanceDpc(
 
         if (NeedTransmitterPoll)
         {
-            BOOLEAN Retry;
-
             KeRaiseIrql(DISPATCH_LEVEL, &Irql);
 
-            Retry = TransmitterPoll(FrontendGetTransmitter(Frontend),
-                                    Instance->Index);
+            TransmitterRetry = 
TransmitterPoll(FrontendGetTransmitter(Frontend),
+                                               Instance->Index);
 
-            if (!Retry) {
+            if (!TransmitterRetry) {
                 PollerInstanceUnmask(Instance, XENVIF_POLLER_EVENT_TRANSMIT);
             } else {
                 (VOID) InterlockedBitTestAndSet(&Instance->Pending,
@@ -627,6 +628,9 @@ PollerInstanceDpc(
             KeLowerIrql(Irql);
         }
     }
+
+    ASSERT(!Enabled || !ReceiverRetry);
+    ASSERT(!Enabled || !TransmitterRetry);
 }
 
 static NTSTATUS
diff --git a/src/xenvif/receiver.c b/src/xenvif/receiver.c
index 6f1fbe5..1f64fab 100644
--- a/src/xenvif/receiver.c
+++ b/src/xenvif/receiver.c
@@ -1959,6 +1959,9 @@ ReceiverRingPoll(
         TailMdl = NULL;
         EOP = TRUE;
 
+        if (Retry)
+            break;
+
         KeMemoryBarrier();
 
         rsp_prod = Ring->Shared->rsp_prod;
@@ -1966,7 +1969,7 @@ ReceiverRingPoll(
 
         KeMemoryBarrier();
 
-        if (rsp_cons == rsp_prod || Retry)
+        if (rsp_cons == rsp_prod)
             break;
 
         while (rsp_cons != rsp_prod && !Retry) {
@@ -2153,7 +2156,9 @@ ReceiverRingPoll(
         KeMemoryBarrier();
 
         Ring->Front.rsp_cons = rsp_cons;
-        Ring->Shared->rsp_event = rsp_cons + 1;
+        if (!Retry)
+            Ring->Shared->rsp_event = rsp_cons + 1;
+
     }
 
     if (!__ReceiverRingIsStopped(Ring))
-- 
2.5.3


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