In cpustat.c it is using the counter index of PCI_PROCESSOR_QUEUE_LENGTH, which is defined as 44. According to the the registry value HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Perflib\009\Counters, 44 is the "Processor Queue Length". According to Microsoft (http://technet.microsoft.com/en-us/library/cc940375.aspx), the value of that counter returns is scaled by 10 by default. It means that if the queue is 2, a value of 20 will be returned. However, I am not seeing that it is scaled back by the zabbix agent anywhere, so it is probably just returning a value like 20 when there are just 2 threads in the queue.

This may be the root cause for ZBX-3170.