Don't log/count event when link timestamp is not udpated.

Summary:
At router reboot, link status is added into records by `syncInterfaces`. Link status added has timestamp = 0 because link doesn't come up (more exactly change status yet). It is advertised to itself, and counter is pushed to ODS with very large propagation time. To eliminate this special case, don't push to  ODS if timestamp = 0.

https://fburl.com/ods/6ccgaf4f --> filter very large propagation for down link event -> looks good.

Reviewed By: xiangxu1121

Differential Revision: D55955501

fbshipit-source-id: c34177a38c73d592f87f27fcf3ecf01f9f56fe6f

openr/decision/LinkState.cpp

@@ -341,7 +341,11 @@ LinkState::mayHaveLinkEventPropagationTime(
   if (adjDb.linkStatusRecords().has_value()) { // link status not recorded
     auto linkStatus =
         adjDb.linkStatusRecords()->linkStatusMap()->find(linkName);
-    if (linkStatus != adjDb.linkStatusRecords()->linkStatusMap()->end()) {
+    // Timestamp is updated when link status changes (over Netlink). But
+    // at router boot-up, link doesn't change status, and so timestamp is
+    // not set and equals to 0 (default value). We ignore this situation.
+    if (linkStatus != adjDb.linkStatusRecords()->linkStatusMap()->end() &&
+        *linkStatus->second.unixTs()) {
       int64_t propagationTime =
           getUnixTimeStampMs() - *linkStatus->second.unixTs();
       if (propagationTime >= 0) { // ignore negative delta (NTP issue)

openr/decision/tests/DecisionTest.cpp

@@ -6562,6 +6562,16 @@ TEST_F(DecisionTestFixture, LinkEventPropagationTime) {
   counters = fb303::fbData->getCounters();
   EXPECT_GE(
       counters["decision.linkstate.down.propagation_time_ms.avg.60"], 100);
+
+  // Down link event with timestamp is not updated, then it's skipped
+  fb303::fbData->resetAllData();
+  adjDb2 = createAdjDb("2", {}, 2);
+  rec1.linkStatusMap()["2/1"].status() = thrift::LinkStatusEnum::DOWN;
+  rec1.linkStatusMap()["2/1"].unixTs() = 0;
+  adjDb2.linkStatusRecords() = rec1;
+  linkState.updateAdjacencyDatabase(adjDb2, kTestingAreaName);
+  counters = fb303::fbData->getCounters();
+  EXPECT_EQ(counters["decision.linkstate.down.propagation_time_ms.avg.60"], 0);
 }
 
 TEST(DecisionPendingUpdates, perfEvents) {