nfd-master: implement ratelimiter for nfd api updates

Implement a naive ratelimiter for node update events originating from
the nfd API. We might get a ton of events in short interval. The
simplest example is startup when we get a separate Add event for every
NodeFeature and NodeFeatureRule object. Without rate limiting we
run "update all nodes" separately for each NodeFeatureRule object, plus,
we would run "update node X" separately for each NodeFeature object
targeting node X. This is a huge amount of wasted work because in
principle just running "update all nodes" once should be enough.

pkg/nfd-master/nfd-master.go

@@ -259,16 +259,34 @@ func (m *nfdMaster) runGrpcServer(errChan chan<- error) {
 
 // nfdAPIUpdateHandler handles events from the nfd API controller.
 func (m *nfdMaster) nfdAPIUpdateHandler() {
+	updateAll := false
+	updateNodes := make(map[string]struct{})
+	rateLimit := time.After(time.Second)
 	for {
 		select {
 		case <-m.nfdController.updateAllNodesChan:
-			if err := m.nfdAPIUpdateAllNodes(); err != nil {
-				klog.Error(err)
-			}
+			updateAll = true
 		case nodeName := <-m.nfdController.updateOneNodeChan:
-			if err := m.nfdAPIUpdateOneNode(nodeName); err != nil {
-				klog.Error(err)
+			updateNodes[nodeName] = struct{}{}
+		case <-rateLimit:
+			// Check what we need to do
+			// TODO: we might want to update multiple nodes in parallel
+			if updateAll {
+				if err := m.nfdAPIUpdateAllNodes(); err != nil {
+					klog.Error(err)
+				}
+			} else {
+				for nodeName := range updateNodes {
+					if err := m.nfdAPIUpdateOneNode(nodeName); err != nil {
+						klog.Error(err)
+					}
+				}
 			}
+
+			// Reset "work queue" and timer
+			updateAll = false
+			updateNodes = make(map[string]struct{})
+			rateLimit = time.After(time.Second)
 		}
 	}
 }