Fix computing of cpu nano core usage

CRI runtimes do not supply cpu nano core usage as it is not part of CRI
stats. However, there are upstream components that still rely on such
stats to function. The previous fix was faulty because the multiple
callers could compete and update the stats, causing
inconsistent/incoherent metrics. This change, instead, creates a
separate call for updating the usage, and rely on eviction manager,
which runs periodically, to trigger the updates. The caveat is that if
eviction manager is completley turned off, no one would compute the
usage.

pkg/kubelet/stats/cadvisor_stats_provider.go

@@ -155,6 +155,14 @@ func (p *cadvisorStatsProvider) ListPodStats() ([]statsapi.PodStats, error) {
 	return result, nil
 }
 
+// ListPodStatsAndUpdateCPUNanoCoreUsage updates the cpu nano core usage for
+// the containers and returns the stats for all the pod-managed containers.
+// For cadvisor, cpu nano core usages are pre-computed and cached, so this
+// function simply calls ListPodStats.
+func (p *cadvisorStatsProvider) ListPodStatsAndUpdateCPUNanoCoreUsage() ([]statsapi.PodStats, error) {
+	return p.ListPodStats()
+}
+
 // ListPodCPUAndMemoryStats returns the cpu and memory stats of all the pod-managed containers.
 func (p *cadvisorStatsProvider) ListPodCPUAndMemoryStats() ([]statsapi.PodStats, error) {
 	infos, err := getCadvisorContainerInfo(p.cadvisor)