datapath-windows: Avoid busy wait in OvsStartIpHelper

Previously, the IP Helper thread would wait for an event
but with a timeout of 0, which resulted in the thread
busy waiting causing high CPU usage by the kernel.
Since the IP Helper thread is only required based on
certain events, it makes sense to wait indefinitely
till we receieve such an event notification to wake up
the thread. This change aims to address this issue.

When OvsEnqueueIpHelperRequest() or OvsInternalAdapterUp()
is called, the ovsNumIpHelperRequests counter is incremented,
but upon consumption of the request, is not decremented.
Since the wakeup logic for the thread is determined by this
counter value, we need to reset the counter back correctly
once the request has been consumed by the IP Helper thread.

Signed-off-by: Shashank Ram <rams@vmware.com>
Acked-by: Yin Lin <linyi@vmware.com>
Signed-off-by: Gurucharan Shetty <guru@ovn.org>

1 files changed, 13 insertions, 2 deletions

diff --git a/datapath-windows/ovsext/IpHelper.c b/datapath-windows/ovsext/IpHelper.c
index d747e8c2e..636cf9526 100644
--- a/datapath-windows/ovsext/IpHelper.c
+++ b/datapath-windows/ovsext/IpHelper.c
@@ -1091,9 +1091,11 @@ OvsInternalAdapterUp(GUID *netCfgInstanceId)
     InsertHeadList(&ovsIpHelperRequestList, &request->link);
     ovsNumIpHelperRequests++;
     if (ovsNumIpHelperRequests == 1) {
+        NdisReleaseSpinLock(&ovsIpHelperLock);
         OvsWakeupIPHelper();
+    } else {
+        NdisReleaseSpinLock(&ovsIpHelperLock);
     }
-    NdisReleaseSpinLock(&ovsIpHelperLock);
 }
 
 
@@ -1455,12 +1457,14 @@ OvsStartIpHelper(PVOID data)
     POVS_IPNEIGH_ENTRY ipn;
     PLIST_ENTRY link;
     UINT64   timeVal, timeout;
+    PLARGE_INTEGER threadSleepTimeout;
 
     OVS_LOG_INFO("Start the IP Helper Thread, context: %p", context);
 
     NdisAcquireSpinLock(&ovsIpHelperLock);
     while (!context->exit) {
 
+        threadSleepTimeout = NULL;
         timeout = 0;
         while (!IsListEmpty(&ovsIpHelperRequestList)) {
             if (context->exit) {
@@ -1468,6 +1472,7 @@ OvsStartIpHelper(PVOID data)
             }
             link = ovsIpHelperRequestList.Flink;
             RemoveEntryList(link);
+            ovsNumIpHelperRequests--;
             NdisReleaseSpinLock(&ovsIpHelperLock);
             req = CONTAINING_RECORD(link, OVS_IP_HELPER_REQUEST, link);
             switch (req->command) {
@@ -1497,6 +1502,7 @@ OvsStartIpHelper(PVOID data)
             KeQuerySystemTime((LARGE_INTEGER *)&timeVal);
             if (ipn->timeout > timeVal) {
                 timeout = ipn->timeout;
+                threadSleepTimeout = (PLARGE_INTEGER)&timeout;
                 break;
             }
             ipAddr = ipn->ipAddr;
@@ -1519,8 +1525,13 @@ ip_helper_wait:
         KeClearEvent(&context->event);
         NdisReleaseSpinLock(&ovsIpHelperLock);
 
+        /*
+         * Wait indefinitely for the thread to be woken up.
+         * Passing NULL as the Timeout value in the below
+         * call to KeWaitForSingleObject achieves this.
+         */
         KeWaitForSingleObject(&context->event, Executive, KernelMode,
-                              FALSE, (LARGE_INTEGER *)&timeout);
+                              FALSE, threadSleepTimeout);
         NdisAcquireSpinLock(&ovsIpHelperLock);
     }
     NdisReleaseSpinLock(&ovsIpHelperLock);